Pump
Pump
Pump
9.1 Introduction
At the heart of all O&M lies the equipment. Across the Federal sector, this equipment varies greatly in age, size, type, model, fuel used, condition, etc. While it is well beyond the scope of this guide to study all equipment types, we tried to focus our efforts on the more common types prevalent in the Federal sector. The objectives of this chapter are the following: Present general equipment descriptions and operating principles for the major equipment types. Discuss the key maintenance components of that equipment. Highlight important safety issues. Point out cost and energy efficiency issues. Highlight any water-related efficiency impacts issues. Provide recommended general O&M activities in the form of checklists. Where possible, provide case studies. The checklists provided at the end of each section were complied from a number of resources. These are not presented to replace activities specifically recommended by your equipment vendors or manufacturers. In most cases, these checklists represent industry standard best practices for the given equipment. They are presented here to supplement existing O&M procedures, or to merely serve as reminders of activities that should be taking place. The recommendations in this guide are designed to supplement those of the manufacturer, or, as is all too often the case, provide guidance for systems and equipment for which technical documentation has been lost. As a rule, this guide will first defer to the manufacturers recommendations on equipment operations and maintenance. Actions and activities recommended in this guide should only be attempted by trained and certified personnel. If such personnel are not available, the actions recommended here should not be initiated.
9.1
Figure 9.1.1. Typical folding lock and tag scissor clamp. This clamp allows for locks for up to 6 different facility staff.
There are well-accepted conventions for lock-and-tag in the United States, these include: No two keys or locks should ever be the same. A staff members lock and tag must not be removed by anyone other than the individual who
installed the lock and tag unless removal is accomplished under the direction of the employer.
Lock and tag devices shall indicate the identity of the employee applying the device(s). Tag devices shall warn against hazardous conditions if the machine or equipment is energized and shall include directions such as: Do Not Start. Do Not Open. Do Not Close. Do Not Energize. Do Not Operate. Tags must be securely attached to energy-isolating devices so that they cannot be inadvertently or accidentally detached during use. Employer procedures and training for lock and tag use and removal must have been developed,
documented, and incorporated into the employers energy control program.
The Occupational Safety and Health Administrations (OSHA) standard on the Control of Hazardous Energy (Lockout-Tagout), found in CFR 1910.147, spells out the steps employers must take to prevent accidents associated with hazardous energy. The standard addresses practices and procedures necessary to disable machinery and prevent the release of potentially hazardous energy while maintenance or service is performed.
9.2
9.2 Boilers
9.2.1 Introduction
Boilers are fuel-burning appliances that produce either hot water or steam that gets circulated through piping for heating or process uses. Boiler systems are major financial investments, yet the methods for protecting these investments vary widely. Proper maintenance and operation of boilers systems is important with regard to efficiency and reliability. Without this attention, boilers can be very dangerous (NBBPVI 2001b).
Figure 9.2.1. Horizontal return fire-tube boiler (hot gases pass through tube submerged in water).
Figure 9.2.2. Longitudinal-drum water-tube boiler (water passes through tubes surrounded by hot gases).
Water-tube boilers are available in sizes ranging from smaller residential type to very large utility class boilers. Boiler pressures range from 15 psi through pressures exceeding 3,500 psi.
Figure 9.2.3. Electric boiler 9.4 O&M Best Practices Guide, Release 3.0
Most people do not realize the amount of energy that is contained within a boiler. Take for example, the following illustration by William Axtman: If you could capture all the energy released when a 30-gallon home hot-water tank flashes into explosive failure at 332F, you would have enough force to send the average car (weighing 2,500 pounds) to a height of nearly 125 feet. This is equivalent to more than the height of a 14-story apartment building, starting with a lift-off velocity of 85miles per hour! (NBBPVI 2001b)
9.5
Tubing By far, the greatest number of forced outages in all types of boilers are caused by tube failures. Failure mechanisms vary greatly from the long term to the short term. Superheater tubes operating at sufficient temperature can fail long term (over many years) due to normal life expenditure. For these tubes with predicted finite life, Babcock & Wilcox (B&W) offers the NOTIS test and remaining life analysis. However, most tubes in the industrial boiler do not have a finite life due to their temperature of operation under normal conditions. Tubes are more likely to fail because of abnormal deterioration such as water/steam-side deposits retarding heat transfer, flow obstructions, tube corrosion (ID and/or OD), fatigue, and tube erosion. Assessment: Tubing is one of the components where visual examination is of great importance because many tube damage mechanisms lead to visual signs such as distortion, discoloration, swelling, or surface damage. The primary NDE method for obtaining data used in tube assessment is contact UTT for tube thickness measurements. Contact UTT is done on accessible tube surfaces by placing the UT transducer onto the tube using a couplant, a gel or fluid that transmits the UT sound into the tube. Variations on standard contact UTT have been developed due to access limitations. Examples are internal rotating inspection system (IRIS)-based techniques in which the UT signal is reflected from a high rpm rotating mirror to scan tubes from the ID especially in the area adjacent to drums; and B&Ws immersion UT where a multiple transducer probe is inserted into boiler bank tubes from the steam drum to provide measurements at four orthogonal points. These systems can be advantageous in the assessment of pitting. Piping - Main Steam For lower temperature systems, the piping is subject to the same damage as noted for the boiler headers. In addition, the piping supports may experience deterioration and become damaged from excessive or cyclical system loads. Assessment: The NDE method of choice for testing of external weld surfaces is WFMT. MT and PT are sometimes used if lighting or pipe geometry make WFMT impractical. Nondrainable sections, such as sagging horizontal runs, are subject to internal corrosion and pitting. These areas should be examined by internal video probe and/or UTT measurements. Volumetric inspection (i.e., ultrasonic shear wave) of selected piping welds may be included in the NDE; however, concerns for weld integrity associated with the growth of subsurface cracks is a problem associated with creep of high-temperature piping and is not a concern on most industrial installations. - Feedwater A piping system often overlooked is feedwater piping. Depending upon the operating parameters of the feedwater system, the flow rates, and the piping geometry, the pipe may be prone to corrosion or flow assisted corrosion (FAC). This is also referred to as erosion-corrosion. If susceptible, the pipe may experience material loss from internal surfaces near bends, pumps, injection points, and flow transitions. Ingress of air into the system can lead to corrosion and pitting. Out-of-service corrosion can occur if the boiler is idle for long periods. Assessment: Internal visual inspection with a video probe is recommended if access allows. NDE can include MT, PT, or WFMT at selected welds. UTT should be done in any location where FAC is suspected to ensure there is not significant piping wall loss.
9.6
Deaerators Overlooked for many years in condition assessment and maintenance inspection
programs, deaerators have been known to fail catastrophically in both industrial and utility
plants. The damage mechanism is corrosion of shell welds, which occurs on the ID surfaces.
Assessment: Deaerators welds should have a thorough visual inspection. All internal welds and selected external attachment welds should be tested by WFMT.
9.7
Boiler heating surfaces Assessment: Use a bright light to inspect the boiler flue collector and heating surfaces. If the vent pipe or boiler interior surfaces show evidence of soot, clean boiler heating surfaces. Remove the flue collector and clean the boiler, if necessary, after closer inspection of boiler heating surfaces. If there is evidence of rusty scale deposits on boiler surfaces, check the water piping and control system to make sure the boiler return water temperature is properly maintained. Reconnect vent and draft diverter. Check inside and around boiler for evidence of any leaks from the boiler. If found, locate source of leaks and repair. Burners and base Assessment: Inspect burners and all other components in the boiler base. If burners must be cleaned, raise the rear of each burner to release from support slot, slide forward, and remove. Then brush and vacuum the burners thoroughly, making sure all ports are free of debris. Carefully replace all burners, making sure burner with pilot bracket is replaced in its original position and all burners are upright (ports up). Inspect the base insulation.
Figure 9.2.4. Adapted from 1999 National Board of Boiler and Pressure Vessel Inspectors incident report summary. 9.8 O&M Best Practices Guide, Release 3.0
Boiler inspections should be performed at regular intervals by certified boiler inspectors. Inspections should include verification and function of all safety systems and procedures as well as operator certification review.
9.9
Install waste heat recovery The magnitude of the stack loss for boilers without recovery is about 18% on gas-fired and about 12% for oil- and coal-fired boilers. A major problem with heat recovery in flue gas is corrosion. If flue gas is cooled, drops of acid condense at the acid dew temperature. As the temperature of the flue gas is dropped further, the water dew point is reached at which water condenses. The water mixes with the acid and reduces the severity of the corrosion problem. - Symptom Flue gas temperature is the indicator that determines whether an economizer or air heater is needed. It must be remembered that many factors cause high flue gas temperature (e.g., fouled water side or fire side surfaces, excess air). - Action Required - If flue gas temperature exceeds minimum allowable temperature by 50F or more, a conventional economizer may be economically feasible. An unconventional recovery device should be considered if the low-temperature waste heat saved can be used to heating water or air. Cautionary Note: A high flue gas temperature may be a sign of poor heat transfer resulting from scale or soot deposits. Boilers should be cleaned and tuned before considering the installation of a waste heat recovery system. Reduce scale and soot deposits Scale or deposits serve as an insulator, resulting in more heat from the flame going up the stack rather than to the water due to these deposits. Any scale formation has a tremendous potential to decrease the heat transfer. - Symptom The best indirect indicator for scale or
deposit build-up is the flue gas temperature. If at the
same load and excess air the flue gas temperature rises
with time, the effect is probably due to scale or deposits.
Scale deposits on the water side and soot deposits on the fire side of a boiler not only act as insulators that reduce efficiency, but also cause damage to the tube structure due to overheating and corrosion.
- Action Required Soot is caused primarily by incomplete combustion. This is probably due to deficient air, a fouled burner, a defective burner, etc. Adjust excess air. Make repairs as necessary to eliminate smoke and carbon monoxide. Scale formation is due to poor water quality. First, the water must be soft as it enters the boiler. Sufficient chemical must be fed in the boiler to control hardness.
9.10
Reduce blowdown Blowdown results in the energy in the hot water being lost to the sewer unless energy recovery equipment is used. There are two types of blowdown. Mud blow is designed to remove the heavy sludge that accumulates at the bottom of the boiler. Continuous or skimming blow is designed to remove light solids that are dissolved in the water. - Symptom Observe the closeness of the various water quality parameters to the tolerances stipulated for the boiler per manufacturer specifications and check a sample of mud blowdown to ensure blowdown is only used for that purpose. Check the water quality in the boiler using standards chemical tests. - Action Required Conduct proper pre-treatment of the water by ensuring makeup is softened. Perform a mud test each time a mud blowdown is executed to reduce it to a minimum. A test should be conducted to see how high total dissolved solids (TDS) in the boiler can be carried without carryover. Recover waste heat from blowdown Blowdown contains energy, which can be captured by a waste heat
recovery system. - Symptom and Action Required Any boiler with a significant makeup (say 5%) is a candidate for blowdown waste heat recovery. Stop dynamic operation on applicable boilers - Symptom Any boiler which either stays off a significant amount of time or continuously varies in firing rate can be changed to improve efficiency. - Action Required For boilers which operate on and off, it may be possible to reduce the firing rate by changing burner tips. Another point to consider is whether more boilers are being used than necessary. Reduce line pressure Line pressure sets the steam temperature for saturated steam. - Symptom and Action Required Any steam line that is being operated at a pressure higher than the process requirements offers a potential to save energy by reducing steam line pressure to a minimum required pressure determined by engineering studies of the systems for different seasons of the year. Operate boilers at peak efficiency Plants having two or more boilers can save energy by load management such that each boiler is operated to obtain combined peak efficiency. - Symptom and Action Required Improved efficiency can be obtained by proper load selection, if operators determine firing schedule by those boilers, which operate smoothly. Preheat combustion air Since the boiler and stack release heat, which rises to the top of the boiler room, the air ducts can be arranged so the boiler is able to draw the hot air down back to the boiler. - Symptom Measure vertical temperature in the boiler room to indicate magnitude of
stratification of the air.
- Action Required Modify the air circulation so the boiler intake for outside air is able to draw from the top of the boiler room.
Typical uses for waste heat include: Heating of combustion air
Makeup water heating Boiler feedwater heating Appropriate process water heating Domestic water heating.
9.11
Reprinted with permission of the National Board of Boiler and Pressure Vessel Inspectors.
Switch from steam to air atomization The energy to produce the air is a tiny fraction of the energy in the fuel, while the energy in the steam is usually 1% or more of the energy in the fuel. - Symptom Any steam-atomized burner is a candidate for retrofit. - Action Required Check economics to see if satisfactory return on investment is available.
(NBBPVI 2001a)
A boiler efficiency improvement program must include two aspects: (1) action to bring the boiler to peak efficiency and (2) action to maintain the efficiency at the maximum level. Good maintenance and efficiency start with having a working knowledge of the components associated with the boiler, keeping records, etc., and end with cleaning heat transfer surfaces, adjusting the air-to-fuel ratio, etc (NBBPVI 2001a). Sample steam/hot-water boiler maintenance, testing and inspection logs, as well as water quality testing log can be found can be found at the end of this section following the maintenance checklists.
9.13
9.2.9.1 Boiler Measure #1: Boiler Loading, Sequencing, Scheduling, and Control
The degree to which a boiler is loaded can be determined by the boilers firing rate. Some boiler manufacturers produce boilers that operate at a single firing rate, but most manufacturers boilers can operate over a wide range of firing rates. The firing rate dictates the amount of heat that is produced by the boiler and consequently, modulates to meet the heating requirements of a given system or process. In traditional commercial buildings, the hot water or steam demands will be considerably greater in the winter months, gradually decreasing in the spring/fall months and finally hitting its low point during the summer. A boiler will handle this changing demand by increasing or decreasing the boilers firing rate. Meeting these changing loads introduces challenges to boiler operators to meet the given loads while loading, sequencing and scheduling the boilers properly. Any gas-fired boiler that cycles on and off regularly or has a firing rate that continually changes over short periods can be altered to improve the boilers efficiency. Frequent boiler cycling is usually a sign of insufficient building and/or process loading. Possible solutions to this problem (Dyer 1991) include adjusting the boilers high and low pressure limits (or differential) farther apart and thus keeping the boiler on and off for longer periods of time. The second option is replacement with a properly sized boiler.
O&M Tip: Load management measures, including optimal matching of boiler size and boiler load, can save as much as 50% of a boilers fuel use.
The efficiency penalty associated with low-firing stem from the operational characteristic of the boiler. Typically, a boiler has its highest efficiency at high fire and near full load. This efficiency usually decreases with decreasing load. The efficiency penalty related to the boiler cycle consists of a pre-purge, a firing interval, and a post-purge, followed by an idle (off) period. While necessary to ensure a safe burn cycle, the pre- and post-purge cycles result in heat loss up the exhaust stack. Short cycling results in excessive heat loss. Table9.2.1 indicates the energy loss resulting from this type of cycling (Dyer 1991).
Table 9.2.1. Boiler cycling energy loss Number of Cycles/Hour 2 5 10 Percentage of Energy Loss 2 8 30
Based on equal time between on and off, purge 1 minute, stack temp = 400F, airflow through boiler with fan off = 10% of fan forced airflow.
9.14
Opportunity Identification Boiler operators should record in the daily log if the boiler is cycling frequently. If excessive cycling is observed, operators should consider the options given above to correct the problem. Boiler operators should also record in the daily log the firing rate to meet the given hot water or steam load. If the boilers firing rate continuously cycles over short periods of time and with fairly small variations in load this should be noted. Seasonal variations in firing rate should be noted with an eye for sporadic firing over time. Corrections in firing rates require knowledge of boiler controls and should only be made by qualified staff. Diagnostic Equipment Data Loggers. The diagnostic test equipment to consider for assessing boiler cycling includes many types of electric data logging equipment. These data loggers can be configured to record the time-series electrical energy delivered to the boilers purge fan as either an amperage or wattage measurement. These data could then be used to identify cycling frequency and hours of operation. Other data logging options include a variety of stand-alone data loggers that record run-time of electric devices and are activated by sensing the magnetic field generated during electric motor operation. As above, these loggers develop a times-series record of on-time which is then used to identify cycling frequency and hours of operation. Energy Savings and Economics Estimated Annual Energy Savings. Using Table 9.2.1 the annual energy savings, which could be realized by eliminating or reducing cycling losses, can be estimated as follows:
where: BL = current boiler load or firing rate, %/100 RFC = rated fuel consumption at full load, MMBtu/hr EFF = boiler efficiency, %/100 EL1 = current energy loss due to cycling, % EL2 = tuned energy loss due to cycling, % H = hours the boiler operates at the given cycling rate, hours
9.15
Estimated Annual Cost Savings. The annual cost savings, which could be realized by eliminating or reducing cycling losses, can be estimated as follows:
An associated energy conservation measure that should be considered, in relation to boiler sequencing and control, relates to the number of boilers that operate to meet a given process or building load. The more boilers that operate to meet a given load, results in lower firing rates for each boiler. Boiler manufacturers should be contacted to acquire information on how well each boiler performs at a given firing rate, and the boilers should be operated accordingly to load the boilers as efficiently as possible. The site should also make every possible effort to reduce the number of boilers operating at a given time. Operation and Maintenance Persistence Most boilers require daily attention including aspects of logging boiler functions, temperatures and pressures. Boiler operators need to continuously monitor the boilers operation to ensure proper operation, efficiency and safety. For ideas on persistence actions see the Boiler Operations and Maintenance Checklist at the end of this section.
9.16
The tuned combustion efficiency values specific to the subject boiler are typically published by the manufacturer. These values, usually published as easy to use charts, will display the optimum combustion efficiency compared to the boiler load or firing rate. Using this information, site personnel can determine the maximum combustion efficiency at the average load of the subject boiler. If the boiler has large variances in load (firing rate) throughout the year, and the given boiler combustion efficiency varies significantly with load (firing rate), the equation referenced below can be calculated for each season, with the appropriate efficiency and fuel consumption for the given season. Tuning the Boiler. The boiler can be tuned by adjusting the air to fuel ratio linkages feeding the boiler burner. Experienced boiler operators will need to adjust the air to fuel linkages accordingly to increase or decrease the given ratios to achieve the optimum excess air and resulting combustion efficiency.
O&M Best Practices Guide, Release 3.0 9.17
Diagnostic Equipment. To accurately measure combustion efficiency, excess air and a host of other diagnostic parameters, a combustion analyzer is recommended. These devices, made by a number of different manufacturers, are typically portable, handheld devices that are quick and easy to use. Most modern combustion analyzers will measure and calculate the following: Combustion air ambient temperature, Ta Stack temperature of the boiler, Ts Percent excess air, % Percent O2, % Percent CO2, % Percent CO, % Nitric Oxide, NX ppm Combustion efficiency, EF A typical combustion analyzer is shown below in Figure 9.2.6. The probe seen in the picture is inserted in a hole in the exhaust stack of the boiler. If the boiler has a heat recovery system in the boiler exhaust stack, such as an economizer, the probe should be inserted above the heat recovery system. Figure 9.2.7 provides example locations for measurement of stack temperature and combustion air temperature readings (Combustion Analysis Basics 2004).
Figure 9.2.6. Combustion analyzer Figure 9.2.7. Example locations combustion analysis
9.18
Energy Savings and Economics Estimated Annual Energy Savings. The annual energy savings, which could be realized by improving combustion efficiency, can be estimated as follows:
where
EFF1 = current combustion efficiency, %
EFF2 = tuned combustion efficiency, % AFC = annual fuel consumption, MMBtu/yr Estimated Annual Cost Savings. The annual cost savings, which could be realized by improving combustion efficiency, can be estimated as follows:
where FC = fuel cost, $/MMBtu Combustion Efficiency Energy Savings and Economics Example Example Synopsis: A boiler has an annual fuel consumption of 5,000 MMBtu/yr. A combustion efficiency test reveals an excess air ratio of 28.1%, an excess oxygen ratio of 5%, a flue gas temperature of 400F, and a 79.5% combustion efficiency. The boiler manufacturers specification sheets indicate that the boiler can safely operate at a 9.5% excess air ratio, which would reduce the flue gas temperature to 300F and increase the combustion efficiency to 83.1%. The average fuel cost for the boiler is $9.00/MMBtu. The annual energy savings can be estimated as:
Operation and Maintenance Persistence Combustion analysis measurements should be taken regularly to ensure efficient boiler operation all year. Depending on use, boilers should be tuned at least annually; high use boilers at least twiceannually.
O&M Best Practices Guide, Release 3.0 9.19
Boilers that have highly variable loads throughout the year should consider the installation of online oxygen analyzers. These analyzers will monitor the O2 in the exhaust gas and provide feedback to the linkages controlling the air to fuel ratios into the boilers burner (DOE 2002). This type of control usually offers significant savings by continuously changing the air to fuel linkages and maintaining optimum combustion efficiencies at all times. It should be noted that even if the boiler has an oxygen trim system, the boiler operators should periodically test the boilers with handheld combustion analyzers to ensure the automated controls are calibrated and operating properly.
Scale formation on the water side of the boiler is due to poor water quality, as such, water must be treated before it enters the boiler. Table 9.2.3 presents the chemical limits recommended for BoilerWater Concentrations (Doty and Turner 2009). The table columns highlight the limits according to the American Boiler Manufacturers Association (ABMA) for total solids, alkalinity, suspended solids, and silica. For each column heading the ABMA value represents the target limit while the column headed Possible represents the upper limit.
Table 9.2.3. Recommended limits for boiler-water concentrations Drum Pressure (psig) 0 to 300 301 to 450 451 to 600 601 to 750 751 to 900 901 to 1,000 1,001 to 1,500 Total Solids ABMA 3,500 3,000 2,500 2,000 1,500 1,250 1,000 Possible 6,000 5,000 4,000 2,500 ---Alkalinity ABMA 700 600 500 400 300 250 200 Possible 1,000 900 500 400 300 250 200 Suspended Solids ABMA Possible 300 250 150 100 60 40 20 250 200 100 50 ---Silica ABMA 125 90 50 35 20 8 2
The second water-side maintenance activity requires an operational de-aerator to remove excess oxygen. Excess oxygen in the feed-water piping can lead to oxygen pitting and ultimately corrosion which can cause pipe failure. As seen in Figures 9.2.8 through 9.2.13, proper de-aerator operation isessential to prevent oxygen pitting which can cause catastrophic failures in steam systems (Eckerlin2006). Diagnostic Equipment Diagnostic equipment consists of a boiler-stack thermometer and water treatment test equipment necessary to properly analyze the boiler water. Local water treatment companies should be contacted to determine the appropriate additives and controlling agents needed for the particular water compositions that are unique to the given community or region.
9.21
Energy Savings and Economics Figure 9.2.14 presents energy loss percentage as a function of scale thickness. This information is very useful in estimating the resulting energy loss from scale build-up.
Estimated Annual Energy Savings The annual energy savings, which could be realized by removing scale from the water side of the boiler, can be estimated as follows:
9.22
where BL = current boiler load or firing rate, %/100 RFC = rated fuel consumption at full load, MMBtu/hr EFF = boiler efficiency, %/100 EL1 = current energy loss due to scale buildup, % EL2 = tuned energy loss with out scale buildup, % H = hours the boiler operates at the given cycling rate, hours Estimated Annual Cost Savings The annual cost savings, which could be realized by removing scale from the water side of the boiler, can be estimated as follows:
where FC = fuel cost, $/MMBtu Boiler Tube Cleaning Energy Savings and Economics Example Example Synopsis: After visually inspecting the water side of a water tube boiler, normal scale 3/64 inch thick was found on the inner surface of the tubes resulting in an estimated 3% efficiency penalty (see Figure 9.2.14). On-site O&M personnel are going to manually remove the scale. The boiler currently operates 4,000 hrs per year, at an average firing rate of 50%, with a boiler efficiency of 82% and a rated fuel consumption at full load of 10MMBtu/hr. The average fuel cost for the boiler is $9.00/MMBtu. The annual energy savings can be estimated as:
9.23
Operation and Maintenance Persistence Boiler operators should record the results of the boiler water-chemistry tests daily. The water-
chemistry tests should be recorded and benchmarked to determine the necessary treatment.
Boiler operators should complete daily records of the de-aerators operation to ensure continuous and proper operation. Boiler operators should take daily logs of stack temperature for trending purposes as this is a
highly diagnostic indication of boiler heat-transfer-surface condition. An increasing stack
temperature can be indicative of reduced heat transfer.
The fire side of the boiler should be cleaned once a year, and is usually mandated by local
emission regulatory committee.
The Boiler Operations and Maintenance Checklist, sample boiler maintenance log, and water quality test report form are provided at the end of this section for review and consideration.
9.24
9.25
9.2.12 Boiler Checklist, Sample Boiler Maintenance Log, and Water Quality Test
Maintenance Frequency Description Boiler use/sequencing Overall visual inspection Comments Turn off/sequence unnecessary boilers Complete overall visual inspection to be sure all equipment is operating and safety systems are in place Compare temperatures with tests performed after annual cleaning Is variation in steam pressure as expected under different loads? Wet steam may be produced if the pressure drops too fast Unstable levels can be a sign of contaminates in feedwater, overloading of boiler, equipment malfunction Check for proper control and cleanliness Check for proper function temperatures Temperatures should not exceed or drop below design limits Verify the bottom, surface and water column blow downs are occurring and are effective Daily X X Weekly Monthly Annually
Follow manufacturers recommended procedures in lubricating all components Check steam pressure
Check burner Check motor condition Check air temperatures in boiler room Boiler blowdown
X X X X
9.26
Boiler Checklist (contd) Description Boiler logs Comments Keep daily logs on: and amount of fuel used Flue gas temperature Makeup water volume Steam pressure, temperature, and amount generated
Type
Look for variations as a method of fault detection Check oil filter assemblies Inspect oil heaters Check boiler water treatment Check flue gas temperatures and composition Check and clean/replace oil filters and strainers Check to ensure that oil is at proper temperature prior to burning Confirm water treatment system is functioning properly Measure flue gas composition and temperatures at selected firing positions recommended O2% and CO2% Fuel Natural gas No. 2 fuel oil No. 6 fuel oil O2% 1.5 2.0 2.5 CO2% 10 11.5 12.5 X X X X
Note: percentages may vary due to fuel composition variations Check all relief valves Check water level control Check for leaks Stop feedwater pump and allow control to stop fuel flow to burner. Donot allow water level to drop below recommended level. Clean pilot and burner following manufacturers guidelines. Examine for mineral or corrosion buildup. Stop fuel flow and observe flame failure. Start boiler and observe characteristics of flame. Look for: leaks, defective valves and traps, corroded piping, condition of insulation Check for proper setting and tightness X X
Check pilot and burner assemblies Check boiler operating characteristics Inspect system for water/ steam leaks and leakage opportunities Inspect all linkages on combustion air dampers and fuel valves Inspect boiler for air leaks Check blowdown and water treatment procedures Flue gases
Check damper seals Determine if blowdown is adequate to prevent solids buildup Measure and compare last months readings flue gas composition over entire firing range
X X X
9.27
Boiler Checklist (contd) Description Combustion air supply Comments Daily Check combustion air inlet to boiler room and boiler to make sure openings are adequate and clean Check pressure gauge, pumps, filters and transfer lines. Clean filters as required. Check belts for proper tension. Check packing glands for compression leakage. Check for air leaks around access openings and flame scanner assembly. Check for tightness and minimum slippage. Check gaskets for tight sealing, replace if do not provide tight seal Inspect all boiler insulation and casings for hot spots Calibrate steam control valves as specified by manufacturer Check for proper operation valves Check water quality for proper chemical balance Follow manufacturers recommendation on cleaning and preparing water side surfaces Follow manufacturers recommendation on cleaning and preparing fire side surfaces Use recommended material and procedures Remove and recondition or replace Clean and recondition feedwater pumps. Clean condensate receivers and deaeration system Clean and recondition system pumps, filters, pilot, oil preheaters, oil storage tanks, etc. Clean all electrical terminals. Check electronic controls and replace any defective parts. Check operation and repair as necessary Make adjustments to give optimal flue gas composition. Record composition, firing position, and temperature. As required, conduct eddy current test to assess tube wall thickness Maintenance Frequency Weekly Monthly X Annually
Check belts and packing glands Check for air leaks Check all blower belts Check all gaskets Inspect boiler insulation Steam control valves Pressure reducing/regulating Perform water quality test Clean water side surfaces
X X X X X X X X X
Inspect and repair refractories on fire side Relief valve Feedwater system
X X X
Fuel system
Electrical systems
X X
9.28
9.29
9.30
Sample Water Quality Test Form Date Softener Total Hardness TDS or Cond. Feedwater Total Hardness pH Bir. No. O-Alk Boiler Water Test TDS or Cond. SiO2 SO3 Poly or PO4 Condensate pH TDS or Cond. Lbs products fed/day Operator Initials
9.31
9.2.13 References
ASME 1994. Consensus Operating Practic es for Control of Feedwater/Boiler Water Chemistry in Modern Industrial Boilers, American Society of Mechanical Engineers, New York, New York. Combustion Analysis Basics. 2004. An Overview of Measurements, Methods and Calculations Used in Combustion Analysis. TSI Incorporated, Shoreview, Minnesota. DOE. 2002. Improve Your Boilers Combustion Efficiency, Tip Sheet #4. In Energy Tips, DOE/ GO 102002-1 506, Office of Industrial Technologies, U.S. Department of Energy, Washington, D.C. DOE. 2009. 2009 Buildings Energy Data Book. Prepared by Oak Ridge National Laboratory for the Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy, Washington, D.C. Available at: http://buildingsdatabook.eren.doe.gov/. Doty, S. and Turner WC. 2009. Energy Management Handbook. Seventh Edition, Fairmont Press, Lilburn, Georgia. Dyer D. 1991. Maples, Glennon Boiler Efficiency Improvement, Boiler Efficiency Institute, Auburn, Alabama, Fifth Edition. Dyer, D.F. and G. Maples. 1988. Boiler Efficiency Improvement. Boiler Efficiency Institute, Auburn, Alabama. Eckerlin H. 2006. Measuring and Improving Combustion Efficiency. In National IAC Webcast Lecture Series 2006, Lecture 2. U.S. Department of Energy, Industrial Assessment Center at North Carolina University, USDOE SAVE ENERGY NOW. Available URL: http://iac.rutgers.edu/lectures2006/arch_lectures.php. EPA. 2003. Wise Rules for Industrial Energy Efficiency A Tool Kit For Estimating Energy Savings and Greenhouse Gas Emissions Reductions. EPA 231-R-98-014, U.S. Environmental Protection Agency, Washington, D.C. EPA. 2006. Heating and Cooling System Upgrades. U.S. Environmental Protection Agency, Washington, D.C. Available URL: http://www.energystar.gov. Nakoneczny, G.J. July 1, 2001. Boiler Fitness Survey for Condition Assessment of Industrial Boilers, BR-1635, Babcock & Wilcox Company, Charlotte, North Carolina. Niles, R.G. and R.C. Rosaler. 1998. HVAC Systems and Components Handbook. Second Edition. McGraw-Hill, New York. NTT. 1996. Boilers: An Operators Workshop. National Technology Transfer, Inc. Englewood, Colorado. OIT. 2001. Modern Industrial Assessments: A Training Manual. Industrial Assessment Manual from the Office of Productivity and Energy Assessment at the State University of New Jersey, Rutgers, for the U.S. Department of Energy Office of Industrial Technology.
9.32
The National Board of Boiler and Pressure Vessel Inspectors (NBBPVI). April 15, 2001a. School Boiler Maintenance Programs: How Safe are The Children. National Board BULLETIN, Fall 1997, Columbus, Ohio. [On-line report]. Available URL: http://www.nationalboard.org/Publications/Bulletin/
FA97.pdf.
The National Board of Boiler and Pressure Vessel Inspectors (NBBPVI). April 15, 2001b. Is preventive maintenance cost effective? National Board BULLETIN, Summer 2000, Columbus, Ohio. [Online report]. Available URL: http://www.nationalboard.org/Publications/Bulletin/SU00.pdf. The National Board of Boiler and Pressure Vessel Inspectors (NBBPVI). April 15, 2001c. 1999 Incident Report. National Board BULLETIN, Summer 2000, Columbus, Ohio. [Online report]. Available URL: http://www.nationalboard.org/Publications/Bulletin/SU00.pdf. Williamson-Thermoflo Company. July 12, 2001. GSA Gas Fired Steam Boilers: Boiler Manual. PartNumber 550-110-738/0600, Williamson-Thermoflo, Milwaukee, Wisconsin. [Online report]. Available URL: http://www.williamson-thermoflo.com/pdf_files/550-110-738.pdf.
9.33
9.34
In contrast to the inverted bucket trap, both types of thermostatic traps allow rapid purging of air at startup. The inverted bucket trap relies on fluid density differences to actuate its valve. Therefore, it cannot distinguish between air and steam and must purge air (and some steam) through a small hole. A thermostatic trap, on the other hand, relies on temperature differences to actuate its valve. Until warmed by steam, its valve will remain wide open, allowing the air to easily leave. After the trap warms up, its valve will close, and no continuous loss of steam through a purge hole occurs. Recognition of this deficiency with inverted bucket traps or other simple mechanical traps led to the development of float and thermostatic traps. The condensate release valve is driven by the level of condensate inside the trap, while an air release valve is driven by the temperature of the trap. A float and thermostatic trap, shown in Figure 9.3.4, has a
O&M Best Practices Guide, Release 3.0 9.35
float that controls the condensate valve and a thermostatic element. When condensate enters the trap, the float raises allowing condensate to exit. The thermostatic element opens only if there is a temperature drop around the element caused by air or other non-condensable gases.
9.36
estimated to be 75%. Calculation of annual energy loss for this example is illustrated below. Estimating steam loss using Figure 9.3.6.
Assume: 3/8-inch diameter orifice steam trap, 50% blocked, 60psia saturated steam system, steam system energized 4,380 h/yr (50% of year), 75% boiler efficiency. Using Figure 9.3.6 for 3/8-inch orifice and 60 psia steam, steam loss = 2,500 million Btu/yr. Assuming trap is 50% blocked, annual steam loss estimate = 1,250million Btu/yr. Assuming steam system is energized 50% of the year, energy loss = 625 million Btu/yr. Assuming a fuel value of $5.00 per million cubic feet (1 million Btuboiler input).
Annual fuel loss including boiler losses = [(625 million Btu/yr)/(75%efficiency) ($5.00/million Btu)] = $4,165/yr.
9.37
from Grashofs equation for steam discharge through an orifice (Avallone and Baumeister 1986) and assumes the trap is energized (leaks) the entire year, all steam leak energy is lost, and that makeup water is available at an average temperature of 60F. Boiler losses are not included in Figure 9.3.6, so must be accounted for separately. Thus, adjustments from the raw estimate read from this figure must be made to account for less than full-time steam supply and for boiler losses. The maximum steam loss rate occurs when a trap fails with its valve stuck in a fully opened position. While this failure mode is relatively common, the actual orifice size could be any fraction of the fully opened position. Therefore, judgment must be applied to estimate the orifice size associated with a specific malfunctioning trap. Lacking better data, assuming a trap has failed with an orifice size equivalent to one-half of its fully-opened condition is probably prudent.
9.38
Thermostatic Steam Trap (Bimetallic and Bellows Steam Traps) Thermostatic traps have, as the main operating element, a metallic corrugated bellows that is filled with an alcohol mixture that has a boiling point lower than that of water. The bellows will contract when in contact with condensate and expand when steam is present. Should a heavy condensate load occur, such as in start-up, the bellows will remain in a contracted state, allowing condensate to flow continuously. As steam builds up, the bellows will close. Therefore, there will be moments when this trap will act as a continuous flow type while at other times, it will act intermittently as it opens and closes to condensate and steam, or it may remain totally closed. These traps adjust automatically to variations of steam pressure but may be damaged in the presence of water hammer. They can fail open should the bellows become damaged or due to particulates in the valve hole, preventing adequate closing. There can be times when the tray becomes plugged and will fail closed.
9.39
Thermodynamic Steam Trap (Disc Steam Trap) Thermodynamic traps have a disc that rises and falls depending on the variations in pressure between steam and condensate. Steam will tend to keep the disc down or closed. As condensate builds up, it reduces the pressure in the upper chamber and allows the disc to move up for condensate discharge. This trap is a good general type trap where steam pressures remain constant. It can handle superheat and water hammer but is not recommended for process, since it has a tendency to air-bind and does not handle pressure fluctuations well. A thermodynamic trap usually fails open. There are other conditions that may indicate steam wastage, such as motor boating, in which the disc begins to wear and fluctuates rapidly, allowing steam to leak through. Other Steam Traps (Thermostatic and Float Steam Trap and Orifice Steam Trap) Float and thermostatic traps consist of a ball float and a thermostatic bellows element. As condensate flows through the body, the float rises or falls, opening the valve according to the flow rate. The thermostatic element discharges air from the steam lines. They are good in heavy and light loads and on high and low pressure, but are not recommended where water hammer is a possibility. When these traps fail, they usually fail closed. However, the ball float may become damaged and sink down, failing in the open position. The thermostatic element may also fail and cause a fail open condition. For the case of fixed orifice traps, there is the possibility that on light loads these traps will pass live steam. There is also a tendency to waterlog under wide load variations. They can become clogged due to particulate buildup in the orifice and at times impurities can cause erosion and damage the orifice size, causing a blow-by of steam.
9.40
Sight glasses can also be used for a visual observation, but have some drawbacks that must be overcome or avoided. First, steam and condensate are both expected to exist upstream and downstream of the trap (live steam on the upstream side and flash steam on the downstream side). Second, the view through a sight glass tends to deteriorate over time because of internal or external fouling. Third, both steam and condensate will appear as clear fluids within the pipe. In response to the first and third concerns, sight glasses have been developed with internal features that allow the proportion of steam and condensate to be identified.
O&M Best Practices Guide, Release 3.0 9.41
Sound Method Mechanisms within steam traps and the flow of steam and condensate through steam traps generate sonic (audible to the human ear) and supersonic sounds. Proper listening equipment, coupled with the knowledge of normal and abnormal sounds, can yield reliable assessments of steam trap working condition. Listening devices range from a screwdriver or simple mechanics stethoscope that allow listening to sonic sounds to more sophisticated electronic devices that allow listening to sonic or sonic and ultrasonic sounds at selected frequencies. The most sophisticated devices compare measured sounds with the expected sounds of working and non-working traps to render a judgment on trap condition. Temperature Method Measuring the temperature of the steam trap is generally regarded as the least reliable of the three basic evaluation techniques. Saturated steam and condensate exist at the same temperature, of course, so its not possible to distinguish between the two based on temperature. Still, temperature measurement provides important information for evaluation purposes. A cold trap (i.e., one that is significantly cooler than the expected saturated steam temperature) indicates that the trap is flooded with condensate, assuming the trap is in service. A flooded trap could mean several things, but barring measurement during startup, when flooding can be expected, generally indicates a problem that needs to be addressed. Downstream temperature measurement may also yield useful clues in certain circumstances. For example, the temperature downstream of a trap should drop off relatively quickly if the trap is working properly (mostly condensate immediately past the trap). On the other hand, the temperature downstream of the trap will be nearly constant if significant steam is getting past the trap. Care must be taken not to use this technique where other traps could affect downstream conditions, however. Temperature measurement methods, like sound measurement, vary tremendously in the degree of sophistication. At the low-end, spitting on the trap and watching the sizzle provides a general indication of temperature. For the more genteel, a squirt bottle filled with water will serve the same purpose. Alternatively, a glove-covered hand can provide a similar level of accuracy. More sophisticated are various types of temperature sensitive crayons or tapes designed to change color in different temperature ranges. Thermometers, thermocouples, and other devices requiring contact with the trap offer better precision. Finally, non-contact (i.e., infrared) temperature measuring devices (sensing thermometers and cameras) provide the precision of thermometers and thermocouples without requiring physical contact. Non-contact temperature measurement makes it easier to evaluate traps that are relatively difficult or dangerous to access closely. Automated Diagnostics In recent years a number of manufacturers have devised self-diagnosing steam trap routines. In most cases these are based on absence or presence of condensate in the trap as measured by either temperature and/or conductivity. These systems can be connected to an energy management and control system to notify facilities staff of condition or failure. While the remote and self diagnosing aspects of these systems is quite attractive, the vendor should make the facility manager aware that once the sensing element is compromised, the system may be outputting incorrect information and thus lead to a false sense of security. While these systems hold great promise, the user needs to be aware that they are another item that needs to be maintained for proper function.
9.42
Recommended time schedule for testing steam traps Process steam traps: Every 3 months High pressure steam traps: Every 6 months Low to medium pressure steam traps: Every 6 months Building heating steam traps: Twice a heating season
At an absolute minimum, all steam traps should be surveyed and tested at least once per year
9.43
Estimated Annual Energy Savings. The annual energy savings, which could be realized by repairing a failed steam trap, can be estimated as follows (DOE 2006).
where DR = discharge rate of steam, lb/hr H = annual hours of operation, hours Estimated Annual Cost Savings. The annual cost savings, which could be realized by repairing a failed steam trap, can be estimated as follows:
where FCS = average fuel cost of steam, $/1,000 lb of steam It should be noted that this cost savings calculation assumes on-site personnel have benchmarked the fuel cost of steam production. This will display how much the site is paying to produce steam, on a $/1,000 lb of steam basis. Steam Trap Replacement Energy Savings and Economics Example Example Synopsis A steam system audit reveals a failed steam trap in a steam line pressurized to 100 psig. The steam trap has an orifice diameter of 1/8 of an inch and results in a loss rate of 52.8 lb/hr (see Table 9.3.1). The line is energized 8,000 hrs/yr and the current fuel costs are $10/1,000 lb of steam. The annual energy savings can be estimated as:
9.44
A Type A Accident Investigation Board determined that the probable cause of the event was a lack of procedures and training, resulting in operational error. Operators had used an in-line gate valve to remove condensate from a steam line under pressure instead of drains installed for that purpose. The board also cited several management problems. There had been no Operational Readiness Review prior to system activation. Laboratory personnel had not witnessed all the hydrostatic and pressure testing, nor had all test results been submitted, as required by the contract. Documentation for design changes was inadequate.
9.45
1991 Event at a Georgia Hospital (DOE 2001c) In June 1991, a valve gasket blew out in a steam system at a Georgia hospital. Operators isolated that section of the line and replaced the gasket. The section was closed for 2 weeks, allowing condensate to accumulate in the line. After the repair was completed, an operator opened the steam valve at the upstream end of the section. He drove to the other end and started to open the downstream steam valve. He did not open the blow-off valve to remove condensate before he opened the steam valve. Water hammer ruptured the valve before it was 20% open, releasing steam and condensate and killing the operator. Investigators determined that about 1,900 pounds of water had accumulated at the low point in the line adjacent to the repaired valve, where a steam trap had been disconnected. Because the line was cold, the incoming steam condensed quickly, lowering the system pressure and accelerating the steam flow into the section. This swept the accumulated water toward the downstream valve and may have produced a relatively small steam-propelled water slug impact before the operator arrived. About 600 pounds of steam condensed in the cold section of the pipe before equilibrium was reached. When the downstream valve was opened, the steam on the downstream side rapidly condensed into water on the upstream side. This flow picked up a 75 cubic foot slug of water about 400 feet downstream of the valve. The slug sealed off a steam pocket and accelerated until it hit the valve, causing it to rupture. Investigators concluded that the accident could have been prevented if the operator had allowed the pipe to warm up first and if he had used the blow-off valve to remove condensate before opening the downstream valve. Maintenance of Steam Traps A steam trap assessment of three VA hospitals located in Providence, RI, Brockton, MA, and West Roxbury, MA was conducted with help of FEMPs SAVEnergy Program. The facilities are served by 15, 40, and 80 psig steam lines. The Providence system alone includes approximately 1,100steam traps. The assessment targeted steam trap performance and the value of steam losses from malfunctioning traps. The malfunctioning traps were designated for either repair or replacement. Included in this assessment was a training program on steam trap testing. The cost of the initial steam trap audit was $25,000 for the three facilities. Estimated energy savings totaled $104,000. The cost of repair and replacement traps was about $10,000. Thus, the cost savings of $104,000 would pay for the implementation cost of $35,000 in about 4 months.
9.46
X X
9.3.11 References
Avallone, E.A. and T. Baumeister, editors. 1986. Marks Standard Handbook for Mechanical Engineers. 9th ed. McGraw-Hill, New York. Climate Technology Initiative. April 7, 2001. Steam Systems. CTI Energy Efficiency Workshop, September 19-26, 1999, Yakkaichi, Japan. Reprinted with permission of the Climate Technology Initiative. DOE. 2006. Inspect and Repair Steam Traps, Steam Tip Sheet 1. In Energy Tips, DOE/GO102006-2248, Industrial Technologies Program, U.S. Department of Energy, Washington, D.C. Gorelik, B. and A. Bandes. August 15, 2001. Inspect Steam Traps for Efficient System. [Online report]. Available URL: http://www.maintenanceresources.com/ReferenceLibrary/SteamTraps/Inspect.htm. Reprinted with permission of Mr. Bruce Gorelik. U.S. Department of Energy (DOE). March 30, 2001a. Steam Trap Performance Assessment. Federal Technology Alert. U.S. Department of Energy (DOE). March 30, 2001b. 1986 Event at Brookhaven National Laboratory. NFS Safety Notes, Issue No. 98-02, November 1998, Office of Operating Experience Analysis and Feedback, Office of Nuclear and Facility Safety [Online report]. Available URL: http://tis.eh.doe.gov/ web/oeaf/lessons_learned/ons/sn9802.html. U.S. Department of Energy (DOE). March 30, 2001c. 1991 Event at a Georgia Hospital. NFS Safety Notes, Issue No. 98-02, November 1998, Office of Operating Experience Analysis and Feedback, Office of Nuclear and Facility Safety [Online report]. Available URL: http://tis.eh.doe.gov/web/oeaf/ lessons_learned/ons/sn9802.html.
9.47
9.4 Chillers
9.4.1 Introduction
A chiller can be generally classified as a refrigeration system that cools water. Similar to an air conditioner, a chiller uses either a vapor-compression or absorption cycle to cool. Once cooled, chilled water has a variety of applications from space cooling to process uses.
The chiller cycle begins in the evaporator coils located in the chiller where the liquid refrigerant flows over the evaporator tube bundles and evaporates, absorbing heat from the chilled water circulating through the tube bundle. The refrigerant vapor, which is somewhat cooler than the chilled water temperature, is drawn out of the evaporator by the compressor. The compressor pumps the refrigerant vapor to the condenser by raising the refrigerant pressure (and thus, temperature). The refrigerant condenses on the cooling water coils of the condenser giving up its heat to the cooling water. The high-pressure liquid refrigerant from the condenser then passes through the expansion device that reduces the refrigerant pressure (and temperature) to that of the evaporator. The refrigerant again flows over the chilled water coils absorbing more heat and completing the cycle. Mechanical compression chillers are generally classified by compressor type: reciprocating, centrifugal, and screw (Dyer and Maples 1995).
9.48
Reciprocating This is a positive displacement machine that maintains fairly constant volumetric flow over a wide range of pressure ratios. They are almost exclusively driven by fixed speed electric motors. Centrifugal This type of compressor raises the refrigerant pressure by imparting momentum to the refrigerant with a spinning impeller, then stagnating the flow in a diffuser section around the impeller tip. They are noted for high capacity with compact design. Typical capacities range from 100 to 10,000 tons. Screw The screw or helical compressor is a positive displacement machine that has a nearly
constant flow performance characteristic. The machine essentially consists of two mating
helically grooved rotors, a male (lobes) and a female (gullies), in a stationary housing. As the
helical rotors rotate, the gas is compressed by direct volume reduction between the two rotors.
Generator Where the dilute solution flows over the generator tubes and is heated by the steam or hot water. Condenser Where the refrigerant vapor from the generator releases its heat of vaporization to the cooling water as it condenses over the condenser water tube bundle.
On a centrifugal chiller, if the condenser water temperature is decreased by 2F to 3F, the system efficiency can increase by as much as 2% to 3%.
Reducing scale or fouling The heat transfer surfaces in chillers tends to collect various mineral and sludge deposits from the water that is circulated through them. Any buildup insulates the tubes in the heat exchanger causing a decrease in heat exchanger efficiency and thus, requiring a large temperature difference between the water and the refrigerant. Purge air from condenser Air trapped in the condenser causes an increased pressure at the compressor discharge. This results in increased compressor horsepower. The result has the same effect as scale buildup in the condenser. Maintain adequate condenser water flow Most chillers include a filter in the condenser water line to remove material picked up in the cooling tower. Blockage in this filter at higher loads will cause an increase in condenser refrigerant temperature due to poor heat transfer. Reducing auxiliary power requirements The total energy cost of producing chilled water is not limited to the cost of operating the chiller itself. Cooling tower fans, condenser water circulating pumps, and chilled water circulating pumps must also be included. Reduce these requirements as much as possible.
9.50 O&M Best Practices Guide, Release 3.0
Use variable speed drive on centrifugal chillers Centrifugal chillers are typically driven by fixed speed electric motors. Practical capacity reduction may be achieved with speed reductions, which in turn requires a combination of speed control and prerotation vanes. Compressor changeouts In many installations, energy saving measures have reduced demand to the point that existing chillers are tremendously oversized, forcing the chiller to operate at greatly reduced loads even during peak demand times. This causes a number of problems including surging and poor efficiency. Replacing the compressor and motor drive to more closely match the observed load can alleviate these problems. Use free cooling Cooling is often required even when outside temperatures drop below the minimum condenser water temperature. If outside air temperature is low enough, the chiller should be shut off and outside air used. If cooling cannot be done with outside air, a chiller bypass can be used to produce chilled water without the use of a chiller. Operate chillers at peak efficiency Plants having two or more chillers can save energy by load management such that each chiller is operated to obtain combined peak efficiency. An example of this is the use of a combination of reciprocating and centrifugal compressor chillers. Heat recovery systems Heat recovery systems extract heat from the chilled liquid and reject
some of that heat, plus the energy of compression, to warm water circuit for reheat and cooling.
Use absorption chilling for peak shaving In installations where the electricity demand curve is dominated by the demand for chilled water, absorption chillers can be used to reduce the overall electricity demand. Replace absorption chillers with electric drive centrifugals Typical absorption chillers require approximately 1.6 Btu of thermal energy delivered to the chiller to remove 1 Btu of energy from the chilled water. Modern electric drive centrifugal chillers require only 0.2 Btu of electrical energy to remove 1 Btu of energy from the chilled water (0.7 kw/ton). Thermal storage The storage of ice for later use is an increasing attractive option since cooling is required virtually year-round in many large buildings across the country. Because of utility demand charges, it is more economical to provide the cooling source during non-air conditioning periods and tap it when air conditioning is needed, especially peak periods.
9.51
Checking all electrical starters, contactors, and relays. Checking all hot gas and unloader operations. Using superheat and subcooling temperature readings to obtain a chillers maximum efficiency. Taking discharge line temperature readings. A sample chiller operations log useful for recording relevant operational efficiency metrics is provide at the end of this section following the chiller maintenance checklist.
9.52
Likewise, the energy input required for any chiller (mechanical compression or absorption) increases as the temperature lift between the evaporator and the condenser increases. Raising the chilled water temperature will cause a corresponding increase in the evaporator temperature and thus, decrease the required temperature lift. A decrease in temperature lift equates to a decrease in energy use. Opportunity Identification The basic chilled water control strategies for chillers using microprocessor-based controllers are presented below: Return Temperature. A chiller controlled by return-water temperature will rely on preset operational instructions based on the return temperature. For example, if the return water temperature increases, indicating an increasing load, the chiller is preprogrammed to respond with greater capacity and thereby mitigating the increased load. Supply Temperature. A chiller controlled by the supply-water temperature functions with a set of water temperatures pre-programmed based on chiller loading. For example, as a space or process calls for greater capacity (i.e., a space temperature is increasing with solar loading) the chiller response is proportional to the call for added capacity. Constant Return. If the chiller is controlled to have a constant return water temperature, the chiller will modulate chilled water supply temperatures to achieve a certain return water temperature over a range of chiller loads. In this case, the chiller operator specifies the desired chilled water return temperature, and the chiller modulates the chilled water supply temperature accordingly to meet this temperature. Outside Air. Water cooled chillers that are located indoors, usually require an outdoor temperature sensor wired into the chillers control panel. Most chiller manufacturers provide outside air temperature sensors that are specific to their chillers, and easily be integrated into the chiller control panel. In this case, the chiller reads the outdoor wet-bulb temperatures and modulates the chilled water temperature based on predefined outdoor air temperatures and chilled-water set-points.
9.53
Zone Temperature. Some chillers come equipped with temperature sensors that read interior zone temperatures, or they have controls that can be integrated into the building automation system (BAS). In this case, the operators can apply chilled water reset strategies based on the interior zone temperatures. In each case, the chiller will usually step up the chilled water temperature to that of the reset value, even if the compressor is in the off cycle. Chilled water reset strategies usually reset the chilled water temperature over a range of about 10F (Webster 2003). Chiller operators should contact their local chiller manufacturers for information on setting appropriate chilled water temperatures. Manufacturers can provide guidance on chilled water modulation at partial loads, and outside air temperatures for the particular chiller. Regardless of the control strategy used to modulate chilled water temperatures, the operators should always keep in mind the impacts on the entire chilled water system. Care should be taken to optimize the entire system, rather than just applying chilled water reset strategies blindly (Webster 2003). It is also important to consider the implications on cooling coils and their ability to regulate the indoor relative humidity ratios within the building, at higher chilled water temperatures. As the chilled water temperatures are increased, the energy/facility managers should closely monitor indoor relative humidity (RH) levels to make sure they are staying in the 55% to 60% RH range. Diagnostic Equipment Opportunities with chillers rely on the use of the chiller controller and/or the BAS for diagnosis. There are situations where neither the controller nor the BAS are available or programmed properly for use. In these cases, portable data loggers for evaluating temperatures are most appropriate. In addition, chiller and chilled water distribution systems usually have temperature and pressure devices hard-mounted to the system. These devices, provided they are accurate, can be used in system diagnostics. Energy Savings and Economics Recognizing that the system efficiency can increase by as much as 2% to 5% by raising the chilled water supply temperature by 2F to 3F, the annual energy savings, which could be realized, can be estimated as follows:
where CEU = chiller energy use, kW H = hours of operation at a given load, h ES = energy savings, %
9.54
Estimated Annual Cost Savings The annual cost savings, which could be realized by increasing chilled water temperatures, can be estimated as follows:
where ER = electric energy rate, $/kWh It should be noted that this cost savings calculation does not account for an electric peak demand reduction. If the facility has a peak demand charge, and the chiller operates everyday with on operational schedule that is coincident with the facilities peak demand, then this calculation could underestimates the cost savings. Chilled Water Supply Temperature Energy Savings and Economics Example Example Synopsis: A water cooled centrifugal chiller currently has a constant 42F supply temperature. After inspection it was determined that the temperature controls can allow modulation up to 45F during low load periods with an estimated energy savings of 2.25%. The operators estimate that the chiller can operate at 45F for 3,000 hrs per year, and the chiller has an electrical load of 300 kW when operating at these low load conditions. The average electric rate is $0.10/kWh. The annual energy savings can be estimated as:
Chiller Measure #2: Condenser Water Temperature Control The effect of reducing condenser water temperature (watercooled chillers only) is very similar to that of raising the chilled water temperature on the supply side, namely reducing the temperature lift that must be supplied by the chiller. These temperatures can be reset downward as outdoor wet-bulb temperatures decrease and during lowload conditions (Webster2003).
O&M Tip: For each 1Fdecrease in condenser cooling water temperature, until optimal water temperature is reached, there is a corresponding percentage decrease in chiller energy use.
It is important to note that the chiller operators need to make sure that the chiller is capable of handling lowered condenser water temperatures. Some chillers are not designed to handle lower condenser water temperatures and can encounter compressor oil return problems. As a default, sitepersonnel should always check with their local chiller manufacturers before lowering the condenser watertemperatures.
9.55
Opportunity Identification Most chillers reach their maximum operating efficiency at the designed peak load. However, chillers operate at the part-load condition most of the time. Resetting the condenser water temperature normally decreases the temperature lift between the evaporator and the condenser, thus increasing the chiller operating efficiency. Therefore, to reset the condenser water temperature to the lowest possible temperature will allow the cooling tower to generate cooler condenser water whenever possible. Note that although lowering the condenser water temperature will reduce chiller energy, it may increase cooling tower energy consumption because the tower fan may have to run longer to achieve the lower condenser water temperature. In addition, some older chillers have condensing water temperature limitations. Consult the chiller manufacturer to establish appropriate guidelines for lowering the condenser water temperature. Diagnostic Equipment Opportunities with chillers rely on the use of the chiller controller and/or the BAS for diagnosis. There are situations where neither the controller not the BAS are available or programmed properly for use. In these cases, portable data loggers for evaluating temperatures are most appropriate. In addition, chiller and chilled water distribution systems usually have temperature and pressure devices hard-mounted to the system. These devices, provided they are accurate, can be used in system diagnostics. Estimated Annual Energy Savings Lowering the condenser water temperature 2F to 3F can increase system efficiency by as much as 2% to 3%. The annual energy savings, which could be realized by reducing condenser temperatures, can be estimated as follows:
where
CEU = chiller energy use, kW
H = hours of operation at a given load, h
ES = energy savings, %
Estimated Annual Cost Savings The annual cost savings, which could be realized by reducing condenser temperatures, can be estimated as follows: where ER = electric energy rate, $/kWh
9.56
It should be noted that this cost savings calculation does not account for an electric peak demand reduction. If the facility has a peak demand charge, and the chiller operates everyday with on operational schedule that is coincident with the facilities peak demand, then this estimate slightly underestimates the cost savings. Condenser Temperature Reset Energy Savings and Economics Example Example Synopsis: A water cooled centrifugal chiller currently has an entering condenser temperature of 55F. After inspection it was determined that the temperature controls can allow modulation down to 52F during low load periods. The operators estimate that the chiller can operate at 52F for 3,000hrs per year, and the chiller has an electrical load of 300kW when operating at these low load conditions. The average electric rate is $0.10/kWh. The annual energy savings can be estimated as:
Turn off/sequence unnecessary chillers Complete overall visual inspection to be sure all equipment is operating and safety systems are in place Check all setpoints for proper setting and function Assess evaporator and condenser coil fouling as required Check temperature per manufacturers specifications
X X X
9.57
Chiller Checklist (contd) Description Comments Daily Perform water quality test Leak testing Check water quality for proper chemical balance Conduct leak testing on all compressor fittings, oil pump joints and fittings, and relief valves Check insulation for condition and appropriateness Verify proper control function including: Hot gas bypass Liquid injection Check settings per manufacturers specification Check settings per manufacturers specification Check settings per manufacturers specification Check settings per manufacturers specification Check settings per manufacturers specification Clean tubes at least annually as part of shutdown procedure As required, conduct eddy current test to assess tube wall thickness Clean tubes at least annually as part of shutdown procedure As required, conduct eddy current test to assess tube wall thickness
X X
Check vane control settings Verify motor load limit control Verify load balance operation Check chilled water reset settings and function Check chiller lockout setpoint Clean condenser tubes Eddy current test condenser tubes Clean evaporator tubes Eddy current test evaporator tubes Compressor motor and assembly Compressor oil system
X X X X X X X X X X
Check all alignments to specification Check all seals, provide lubrication where necessary Conduct analysis on oil and filter Change as required Check oil pump and seals Check oil heater and thermostat Check all strainers, valves, etc.
Check all electrical connections/ terminals for contact and tightness Assess proper water flow in evaporator and condenser Add refrigerant as required. Record amounts and address leakage issues.
X X X
9.58
__________degF CW Temperature Differential Condenser Temperature Condenser Pressure Cooling Tower Makeup Water CHW Makeup Water Operator Initials
9.59
9.4.12 References
Dyer, D.F. and G. Maples. 1995. HVAC Efficiency Improvement. Boiler Efficiency Institute, Auburn, Alabama. The Alliance for Responsible Atmospheric Policy (TARAP). August 3, 2001. Arthur D. Little Report, Section 7 Chiller. [Online report]. Available URL: http://www.arap.org/adlittle/7.html. Trade Press Publishing Corporation. August 6, 2001. Energy Decisions, May 2000, Chiller Preventive Maintenance Checklist. [Online]. Available URL: http://www.facilitiesnet.com/fn/NS/ NS3n0eb.html|ticket=1234567890123456789112925988. Webster T. 2003. Chiller Controls-Related Energy Saving Opportunities in Federal Facilities. LBNL 47649, prepared by the University of California for Lawrence Berkeley National Laboratory, Berkeley, California.
9.60
1. 2. 3. 4. 5. 6. 7. 8. 9.
Hot water from chiller Flow control valve Distribution pipes and nozzles Draft eliminators Centrifugal blower Make-up water infeed Float valve Collection basin Strainer
Bleed water Cooled water to chiller Fan drive Drive shaft Gear box Propeller fan Air intake louvers
Note: Items 3 and 5 not shown in Figure 9.5.2. Reprinted with permission of Washington State University Cooperative Extension Energy Program.
Figure 9.5.2. Direct or open cooling tower O&M Best Practices Guide, Release 3.0
9.61
2. Indirect or closed cooling tower An indirect or closed cooling tower circulates the water through tubes located in the tower. In this type of tower, the cooling water does not come in contact with the outside air and represents a closed system.
9.62
Legionella may be found in water droplets from cooling towers, which may become airborne and become a serious health hazard if inhaled by a human. The lung is a warm and moist environment, which presents perfect conditions for the growth of such a disease. Common symptoms on patients with legionnaires disease are cough, chills, and fever. In addition, muscle aches, headache, tiredness, loss of appetite, and, occasionally, diarrhea can also be present. Laboratory tests may show decreased function of the kidneys. Chest x-rays often show pneumonia.
8. Follow your water treating companys recommendations regarding chemical addition during startup and
continued operation of the cooling system. Galvanized steel cooling towers require special passivation
procedures during the first weeks of operation to prevent white rust.
9. Before starting the fan motor, check the tightness and alignment of drive belts, tightness of mechanical holddown bolts, oil level in gear reducer drive systems, and alignment of couplings. Rotate the fan by hand and ensure that blades clear all points of the fan shroud. 10. The motor control system is designed to start and stop the fan to maintain return cold water temperature. The fan motor must start and stop no more frequently than four to five times per hour to prevent motor overheating. 11. Blowdown water rate from the cooling tower should be adjusted to maintain between two to four concentrations of dissolved solids.
9.63
9.64
Water leaves a cooling tower system in any one of four ways: 1. Evaporation: This is the primary function of the tower and is the method that transfers heat from the cooling tower system to the environment. The quantity of evaporation is not a subject for water efficiency efforts (although improving the energy efficiency of the systems you are cooling will reduce the evaporative load on your tower). Evaporative losses relate to the specifics of the system and environment. In rough terms, for every 10F of water temperature drop across the tower, there is an evaporative loss of approximately 1percent, equating, on average, to 2.5 to 4.0gpm per 100 tons of capacity. 2. Blowdown or Bleed-off: When water evaporates from the tower leaves behind dissolved and suspended substances. If left unchecked, these chemicals will lead to basin water with increasing concentrations of total dissolved solids (TDS). If the concentration gets too high, the solids can come out of solution and cause scale to form within the system and/or the dissolved solids can lead to corrosion problems. Additional problems may arise by creating conditions conducive to biofouling. To mediate this problem, a certain amount of water is removed from the cooling tower this water is referred to as blowdown or bleed off. As this water is being removed, the same quantity is being reintroduced and is called make up. Carefully monitoring and controlling the quantity of blowdown and make up provides the most significant opportunity to conserve water in cooling tower operations. 3. Drift: A comparatively small quantity of water may be carried from the tower not as vapor but as mist or small droplets. Drift loss is small compared to evaporation and blow-down, and is controlled with baffles and drift eliminators. While estimates of drift losses range well below 1% of tower flow rate, on larger towers these losses can add up. 4. Basin Leaks/Overflows: Properly operated towers should not have leaks or overflows. In addition to carefully controlling tower operation, other water efficiency opportunities arise from using alternate sources of make-up water. Sometimes water from other equipment within a facility can be recycled and reused for cooling tower make-up with little or no pre-treatment, including the following: Air handler condensate (water that collects when warm, moist air passes over the cooling coils in air handler units). This reuse is particularly appropriate because the condensate has a low mineral content, and typically is generated in greatest quantities when cooling tower loads are the highest. Water used in a once through cooling system. Pretreated effluent from other processes, provided that any chemicals used are compatible with
the cooling tower system.
High-quality municipal wastewater effluent or recycled water (where available).
9.65
9.66
Consider measuring the amount of water lost to evaporation. Some water utilities will provide
a credit to the sewer charges for evaporative losses, measured as the difference between metered
make-up water minus metered blowdown water.
Consider a comprehensive air handler coil maintenance program. As coils become dirty or
fouled, there is increased load on the chilled water system in order to maintain conditioned air
set point temperatures. Increased load on the chilled water system not only has an associated
increase in electrical consumption, it also increases the load on the evaporative cooling process
which uses more water.
9.67
X X
X X
X X X X X X X X
Check belts and pulleys Adjust all belts and pulleys Check lubrication Check motor supports and fan blades Motor alignment Check drift eliminators, louvers, and fill Clean tower Check bearings Motor condition
X X X
9.68
9.5.10 References
FEMP 2008. Federal Energy Management Program - Water Best Management Practices. Available on line at URL: http://www1.eere.energy.gov/femp/water/water_bmp.htm. Marley Cooling Technologies. July 6, 2001a. Cooling Information Index. Reprinted with permission of Marley Cooling Technologies. http:// www.trane.com/commercial/library/vol34_2/admapn018en_0105.pdf. Marley Cooling Technologies. September 2, 2002b. Sigma F Series. [Online report]. Available URL: http://www.marleyct.com/sigmafseries.htm. Reprinted with permission of Marley Cooling Technologies. Suptic, D.M. April 13, 2001. A Guide to Trouble-Free Cooling Towers: A basic understanding of cooling tower operation and maintenance will help keep a cooling water system running in top condition, year after year, June 1998, RSES Journal. [Online report]. Available URL: http://www.pace-incorporated.com/ maint1.htm. Reprinted with permission of RSES Journal. Washington State University Cooperative Extension Energy Program (WSUCEEP). April 24, 2001. Optimizing Cooling Tower Performance, WSUEEP98013 [Online report]. Reprinted with permission of Washington State University Cooperative Extension Energy Program.
9.69
9.70
9.6.6 Maintenance
The ability of an EMCS to efficiently control energy use in a building is a direct function of the data provided to the EMCS. The old adage garbage in - garbage out could not hold more truth than in an EMCS making decisions based on a host of sensor inputs. For a number of reasons, the calibration of sensors is an often overlooked activity. In many ways, sensors fall into the same category as steam traps: if it doesnt look broken - dont fix it. Unfortunately, as with steam traps, sensors out of calibration can lead to enormous energy penalties. Furthermore, as with steam traps, these penalties can go undetected for years without a proactive maintenance program.
9.71
The following is a list of sensors and actuators that will most need calibration (PECI 1997): Outside air temperature Mixed air temperature Return air temperature Discharge or supply air temperature Coil face discharge air temperatures Chilled water supply temperature Condenser entering water temperature Heating water supply temperature Wet bulb temperature or RH sensors Space temperature sensors Economizer and related dampers Cooling and heating coil valves Static pressure transmitters Air and water flow rates Terminal unit dampers and flows.
Sensor and actuator calibration should be an integral part of all maintenance programs.
9.72
The construction of the building, including the types of windows, insulation, and overall orientation, contributes to its ability to retain conditioned air. This coupled with the internal heating and cooling loads in the building will dictate when the HVAC system should be cycled during the day. Direct Digital Control (DDC) Optimal Start/Stop Most DDC systems have optimal start-stop programs with software algorithms that assess indoor and outdoor temperatures and, based on adaptive learning, the DDC system will activate the buildings HVAC system at different times each day. This technology is one of the most energyefficient HVAC control programs available and should be utilized whenever possible. Other DDC systems have the ability to program preset start-stop times for the buildings HVAC system. In this case, the building operators should try to start the HVAC system as close to the tenants arrival as possible. The operators should also consider applying different start times based on average outdoor air temperatures versus times of extreme outdoor air temperatures. DDC Holiday Scheduling If the building has a DDC control system, it will typically come equipped with a holiday scheduling feature. Building operators should utilize this feature to turn off the buildings HVAC system during unoccupied periods and holidays. In addition to unoccupied periods and holidays, many DoD facilities, such as barracks, training facilities, and mess halls, will go unoccupied for periods of time when troops are deployed, therefore they should have scheduling adjusted accordingly. It should be noted that if the building is located in a humid climate, the HVAC system should be put into standby mode and turned on to maintain the humidity limits and unoccupied setback temperatures within the facility. Building operators should periodically review their DDC codes to make sure the HVAC schedules matches the tenant schedules as closely as possible. If the building operators have to implement overrides to handle extreme weather conditions or special occupancy circumstances, these overrides should be recorded and removed as soon as possible. In buildings with electromechanical and pneumatic controls, the building operators should at a minimum apply a start-stop schedule based on historic data relating to the amount of time it takes to condition the building. In general, when the HVAC system is turned off, the building operators need to ensure that all of the HVAC fans and pumps are turned off. Although it might be necessary to continuously operate the building chillers and boilers, the buildings fans and pumps can be turned off when the HVAC system is not operating. Temperature and Pressure Setpoints Temperature setpoints in buildings can typically be programmed using the proportional integral (PI) control loop. If the PI control loop is used, the site must ensure that the throttling range is not too small (DDC Online 2006b). The throttling range relates to the gap between the heating setpoint and cooling setpoint. The larger this gap is, the less energy the site will use to condition the interior air. Guidelines on indoor temperature setpoints for energy efficiency target the heating season setpoint at between 68F - 72F and the cooling season setpoint at between 72F - 78F. The optimal seasonal setpoint (balancing thermal comfort with energy efficiency) will be a function of type of activity taking place in the space and the ambient relative humidity.
9.73
While some facilities target 68F heating and 78F cooling setpoints, they are not operated at these temperatures because of occupant complaints. Regardless of the chosen setpoints, facility managers should strive to have the largest throttling range (or dead-band gap) between the two setpoints. This ensures that the HVAC system will not slightly overcool the building, causing the building to immediately go into heating mode, and then slightly overheat the building, causing it to go back into cooling mode. This type of constant cycling is inefficient, hard on equipment, and causes the building to constantly hunt for the right temperature. As previously mentioned, the building operators should also implement a nighttime or unoccupied setback temperature. The unoccupied setback for heating should be 5F to 10F cooler than the occupied setpoint, and the unoccupied setback for cooling should be 5F to 10F warmer than the occupied setpoint. In humid climates, the underlying activator of the system should be the relative humidity ratios. As long as these ratios are met, the interior temperatures should be allowed to float over the preset unoccupied setpoints. The temperature setpoint methodology is also valid for electromechanical and pneumatic controls. The only difference may be in the allowable control points two are typical with electromechanical systems. Pressure Setpoints
Based on energy and O&M audits of a variety of Federal facilities, many air-side static Have occupancy patterns or space layouts changed? Are HVAC pressure setpoints fall in range of and lighting still zoned to efficiently serve the spaces? the 1.9 water column (w.c.) to Have temporary occupancy schedules been returned to original 2.6 w.c. This is far higher than settings? necessary where most variable Have altered equipment schedules or lockouts been returned to air volume (VAV) systems are original settings? intended to operate in the 1 Is equipment short-cycling? to 1.5 w.c. range (Lundstrom Are time-clocks checked monthly to ensure proper operation? 2006). If this type of operation Are seasonally changed setpoints regularly examined to ensure is encountered, the site should proper adjustment? investigate the system to make Have any changes in room furniture or equipment adversely affected sure the VAV fans are operating thermostat function? (Check thermostat settings or other controls that and controlling properly. These occupants can access.) high static pressure readings can Are new tenants educated in the proper use and function of sometimes be caused by site staff thermostats and lighting controls? looking to make a quick fix when one of the fans is not operating or controlling properly. This could also be caused by a failed static pressure sensor, failed inlet vane controls, slipping belts or breached ductwork. In any case, the building operator should determine the design air-side static pressure setpoint for the particular air-handling unit to ensure the current operation is as close to this value as possible. The operator should identify the location of the static pressure gauges they should be installed about 2/3of the way down the longest stretch of ductwork. In DDC control systems, some HVAC operators encourage unoccupied pressure setpoint reductions to be implemented in conjunction with the unoccupied temperature setpoint changes. This offers greater energy savings in VAV systems by allowing for a larger dead-band temperature range and less air to be circulated through the building.
9.74 O&M Best Practices Guide, Release 3.0
As staff perform certain maintenance tasks to prepare equipment for heating or cooling seasons, they should also review and adjust operational strategies seasonally. EMCS Measure #2: HVAC Tune-Up and Maintenance Some of the most important HVAC tune-up and maintenance activities a site should consider are related to the following: valves, filters, coil cleanings, sensor calibration, damper operation, belt system checks, system override correction, and air/water flow analysis. Valves Control valves in HVAC systems are used to control the amount of hot or chilled water that circulates through heating or cooling coils. While a necessary component, control valves are notorious for failing. Unfortunately, when a control valve failure occurs, it often goes unnoticed by site staff because it is difficult to assess visually. Common control valve problems/malfunctions include valves that have been manually overridden in the open position, valves stuck in a fixed position, valves that are leaking, and valves that are incorrectly wired usually backwards. One method of valve diagnosis starts with the DDC system. Through the DDC system, an operator will determine if a particular heating coil is hot (i.e., is being supplied with hot water). This will be evident through the system reported as a temperature at the coil. Next, the operator will make sure the zone served by this coil is actually calling for heat; this is represented in the system as a request for service. If the zone is not calling for heat, yet the coil is hot, the operator should examine the control valve for either leakage or manual override. This same procedure holds true for cooling coils. Another method of valve diagnosis again makes use of the DDC system. In this scenario, the operator uses the system to fully close both the heating and cooling valves or he can manually override them. Once done, the operator then reviews the air temperatures on either side of the heating/cooling coils for which there should not be more than a 2F to 4F temperature difference between the two temperature sensors. If the temperature difference exceeds this range, the operator should consider either control valve or temperature sensor malfunction. Sensor Calibration The HVAC temperature, pressure, relative humidity and CO2 sensors within a building have certain calibration limits that they operate within. The accuracy of a given sensor is primarily a function of the sensor type, with accuracy of all sensors usually degrading over time. Accordingly, as a general maintenance function, sensor assessment and calibration should be a routine function. Refer to manufacturers data for the recommendations of assessment and calibration. As with valves, damper operation can be verified using a DDC control system. Through this system, a facility manager can activate the damper to the fully open and then fully closed position while a colleague in the field verifies this function. If a particular damper is not actuating as it should, the linkages and actuator should be examined for proper connection and operation. During this process, field staff should also verify that all moving parts are properly lubricated and seals are in goodshape.
9.75
Because economizers are dampers that interact with outside air, buildings where these are installed should receive special attention. In addition to the above procedure, economizer dampers should be checked at a higher frequency to ensure proper modulation, sealing, and sensor calibration. The temperature and/or humidity (i.e., enthalpy) sensor used to control the economizers should be part of a routine calibration schedule. Belt-Driven System Belt-driven systems are common in HVAC fan systems. Belt drives are common because they are simple and allow for driven equipment speed control, which is accomplished through the adjustment of pulley size. While belt-drive systems are generally considered to be efficient, certain belts are more efficient than others. Standard belt drives typically use V-belts that have a trapezoidal cross section, and operate by wedging themselves into the pulley. These V-belts have initial efficiencies on the order of 95% to 98%, which can degrade by as much as 5% over the life of the system, if the belts are not periodically re tensioned (DOE 2005b). If the fans currently have standard V-belts, retrofit options for consideration include cogged-Vbelts or synchronous belts and drives. In both cases, efficiency gains on the order of 2% to 5% are possible, depending on the existing belt and its condition. It should be noted that cogged-V-belts do not require a pulley change as part of the retrofit while the synchronous belt retrofit does. System Overrides System overrides that are programmed into the buildings DDC systems should be periodically checked. System overrides are sometimes necessary to handle extreme weather conditions, occupancy conditions, or special events. As these are programmed, a special note should be made of what was over-ridden, for what purpose, and when it can be reset. The site should implement a continuous override inspection program to look at all of the overrides that have been programmed into the DDC system and to make sure they are removed as soon as possible. Simultaneous Heating and Cooling In dry climates that do not have a need to simultaneously heat and cool the air to control the relative humidity, it is generally advised that the heating should be disabled whenever the cooling system is activated and vice versa. In pneumatic and electromechanical systems, the building operator may have to manually override the heating and cooling system to accomplish this. With DDC systems installed in areas not requiring dehumidification the system should be programmed to lock out the hot-water pumps during high ambient conditions (e.g., outdoor air temperatures above 70F) and lock out the chilled water pumps during low ambient conditions (e.g., outdoor air temperatures below 60F to 55F). This will ensure that only the necessary service is provided and eliminate the wasteful practice of unnecessary simultaneous heating and cooling. Where simultaneous heating and cooling is required (e.g., in humid climatic regions) to remove the moisture from the conditioned air, and then to heat the air back up to the required setpoint temperatures, building operators should check for proper operation. As noted above, checks should be made to ensure temperature dead-band setting is far enough apart that it does not cause the HVAC system to continuously hunt.
9.76
Since the Custom House generally experiences a summer peak of about 2,000 kW, this means that GSA is obligated to pay for at least 1,600 kW during these off-peak months. However, the facility is a conventional Federal office building with a low load factor, and barely reaches peaks of 1,000 kW from December to March. At more than $28 per kW, the Custom House regularly pays its utility (PECO Energy) over $15,000 per month during those four months (as well as additional sums in the shoulder months of October, November, April, and May) for power it does not even draw.
9.77
With this in mind, GSA requested that FEMP conduct a study on the potential to cost-effectively reduce its peak demand. The central component of FEMPs recommendation was a precooling strategy where GSA would turn on its chilled water plant very early in the morning (as opposed to the usual 6 A.M.) on hot summer days. In addition, FEMP recommended that the chilled water valves in the buildings roughly one thousand perimeter induction units be tripped to a fail-open position during these early morning hours so that the facility would actually be somewhat overcooled. The idea was to utilize the circa 1934 buildings substantial mass as a thermal storage medium, which could then absorb heat and provide cool-temperature radiation throughout the day, mitigating the customary afternoon power peak. GSA adopted this strategy, and working with their operations and maintenance contractor developed a multi-part plan to reduce the buildings peak through early morning pre-cooling and afternoon demand-limiting. The key elements are: If the outside air exceeds 70F at 2 A.M., one of the facilitys two 650-ton chillers is turned on
and programmed to produce 42F chilled water;
All induction unit chilled water valves are set to a full-open position during the early morning; At 9 A.M., the chilled water temperature is raised to 46F and induction unit control reverts to the tenants (the units have no re-heat coils but the unit controls can be set towards warmer to reduce or eliminate the flow of chilled water through them); If demand reaches 1,500 kW and is still rising by 12 noon, the chilled water temperature is raised again, to 48F; Only one of the two 650-ton chillers is allowed to operate at any given time. In the beginning of summer 2005, the team executed the strategy manually, using control system overrides for chiller operation and bleeding the air out of the pneumatic lines to open the induction unit valves. Once the team gained confidence in this strategy, the buildings controls contractor was called in to help automate it within the energy management control system (installed in 2003 as part of a Super Energy Savings Performance Contract). As a result, the operations team was able to keep the facilitys peak demand down to 1,766kW over the summer (defined by the PECO tariff as June though September), as opposed to the 2,050kW or higher that would likely have been reached. GSA benefited directly from the reduced demand in the summer, saving an estimated $26,000 (see Table 9.6.1) in those four months alone.
9.78
Table 9.6.1. Custom House demand reduction and savings 2005-2006 Month Expected Peak (kW)* 1,900 2,050 2,050 1,900 1,640 1,640 1,640 1,640 1,640 1,640 1,640 1,850 Actual Peak (kW)* 1,766 1,692 1,692 1,711 1,640 1,448 1,015 992 961 953 1,393 1,646 Billed Peak (kW)** 1,766 1,692 1,697 1,711 1,604 1,448 1,413 1,413 1,413 1,413 1,413 1,646 Peak Reduction (kW) 134 358 353 189 36 192 227 227 227 227 227 204 kW Value
June 2005 July 2005 August 2005 September 2005 October 2005 November 2005 December 2005 January 2006 February 2006 March 2006 April 2006 May 2006 Total Savings
*
$3,410 $9,109 $8,982 $4,809 $916 $4,885 $5,776 $6,134 $6,134 $6,134 $6,134 $5,512 $67,934
**
June - Sept. 05 and May 06 figures are projected, without pre-cooling; October through April numbers represent 80% of projected summer peak maximum (see orange-shaded cells) Dec. 05 - April 06 figures represent 80% of actual summer peak maximum (see green-shaded cells).
GSA reaped even greater savings from the reduced ratchet charges during the winter months. The ratchet clause set the minimum demand charge for the October through May bills at 1,413kW (80percent of the 1,766kW summer peak). While the previous four summers average peak was 2,080kW, FEMP conservatively estimated that 2,050kW would have been 2005s peak draw (this is a conservative estimate because the summer of 2005 was an unusually hot one in the mid-Atlantic). Since 80 percent of 2,050 is 1,640, this figure was used to estimate the ratchet savings i.e., to represent what the billed peak would have been without the pre-cooling. The 227kW reduction (1640 1413) translated to more than $30,000 in savings for the five months of December through April; additional ratchet relief in October, November, and May made for a total (including the $26,000 in direct summer months savings) of roughly $68,000. In sum, the Custom Houses pre-cooling thermal storage experiment has been an enormous success. The GSA avoided almost $70,000 in demand charges during the first year (2005-6). GSA concluded at a lessons learned meeting that the GSA should declare summer 2005s usage was only 0.5 percent higher, despite the fact that it had 4.3percent more cooling degree days. Moreover, a regression plotting the four previous summers kWh consumption against the number of cooling degree days in each revealed that summer 2005s actual consumption was 2percent less than what the model predicted. The facilitys summer 2006 usage fell a remarkable 7.5 percent below the regressions prediction.
9.79
X X X X X X X X X
Check sensors
X X
9.80
9.6.11 References
DDC Online. 2006a. Introduction to Direct Digital Control Systems. Chapter 1, Direct Digital Controls Online. Available URL: http://www.ddc-online.org/. DDC Online. 2006b. Control Response. Chapter 2, Direct Digital Controls Online. Available URL: http://www.ddc-online.org/. DOE. 2005b. Replace V-Belts with Cogged or Synchronous Belt Drives. In Motor Systems Tip Sheet #5, DOE/GO-102005-2060, U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Washington, D.C. FEMP 2007. GSAs Cool Coup at the Philadelphia Custom House. FEMP Focus, Fall 2007. U.S. Department of Energy, Federal Energy Management Program. Washington D.C. Lundstrom C. 2006. Top Recommissioning Measures to Maintain Efficiency. EMC Engineers Inc., Energy. PECI. 1997. Energy Management Systems: A Practical Guide. Portland Energy Conservation, Inc., Portland, Oregon. PECI. 1999. Operations and Maintenance Assessments. Portland Energy Conservation, Inc. Published by the U.S. Environmental Protection Agency and the U.S. Department of Energy.
9.81
9.82
9.7.5 Maintenance
Proper maintenance for air handling systems includes scheduled filter replacement, coil cleaning, duct integrity evaluation, damper cleanliness and function.
9.83
9.84
An Efficient Building Can Reduce Costs Even More. Although the building was completed in 1994 and has an energy use intensity of 54kBtu/sqftyr, well below the average 70kBtu/sqft-yr for typical office buildings in Oakland, the tune-up team managed to find numerous cost-effective savings measures. One of the findings of the program was that poor sensor locations in the air handlers have been wasting over $27,000 per year. By simply moving sensors to locations that are more representative of the air stream of interest, the existing control algorithms work as they were originally intended. In another case, air was flowing through the ducts in the reverse direction of the intended design. Functional testing showed that under certain conditions, air from one hot deck supply fan was flowing up the common supply shaft and back feeding through the other fan. The R-Cx team recommended controlling both 5th floor & penthouse fans in unison to prevent this problem. Expert analysis required to identify this problem was paid for by the BTU program and building owners paid relatively little to implement the measures. The investigation phase of the project included analysis of trended data logs and extensive functional testing of the HVAC equipment. A total of 12 operational deficiencies were observed in the air handling systems. The problems with the greatest potential for energy savings were thoroughly analyzed and corrective measures were recommended. The project team also made specific recommendations on how to improve the operation and comfort of the facility on other nonenergy related issues. Improvements Save Energy and Increase Comfort. Identification, documentation and implementation of non-energy measures can often improve occupant comfort, reduce operator workload and generally improve the operation of the facility. Examples of such measures at the Ronald V. Dellums Federal Building included: Cleaning and calibrating airflow-monitoring stations on supply and return fans. This corrective measure allowed proper tracking of the return fans speed, which helped maintain the proper pressurization within the building. Adding an auto-zero calibration feature to the VAV box control programs. This ensured that
each occupant received the correct airflow in the work area.
Adjusting the valve actuators and positioners serving the chilled water coils to reduce hunting
and increase coil capacity.
9.85
System integrity
Dampers
Filter assemblies
Coils
9.7.7 References
Department of Energy (DOE). 2005. Actions You Can Take to Reduce Cooling Costs. PNNL-SA-45361; U.S. Department of Energy, Federal Energy Management Program, Washington, D.C. Better Bricks. 2008. Bottom Line Thinking on Energy Building Operations. Northwest Energy Efficiency Alliance. Available at URL: http://www.betterbricks.com. QuEST 2004. Retro-Commissioning Process Finds Energy Cost Savings in Air Handling Systems. QuEST Building Tune-Up Program. Quantum Energy Services & Technologies, Inc., Berkeley, California.
9.86
9.8 Fans
9.8.1 Introduction
The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) defines a fan as an air pump that creates a pressure difference and causes airflow. The impeller does the work on the air, imparting to it both static and kinetic energy, varying proportion depending on the fan type (ASHRAE 1992).
Reprinted with permission of The Institute of Agriculture and Natural Resources, University of Nebraska.
9.87
Tube-axial fans A tube-axial fan (Figure 9.8.3) consists of a tube-shaped housing, a propellershaped blade, and a drive motor. Vane-axial fans (Figure 9.8.4) are a variation of tube-axial fans, and are similar in design and application. The major difference is that air straightening vanes are added either in front of or behind the blades. This results in a slightly more efficient fan, capable of somewhat greater static pressures and airflow rates.
Reprinted with permission of The Institute of Agriculture and Natural Resources, University of Nebraska.
Reprinted with permission of The Institute of Agriculture and Natural Resources, University of Nebraska.
9.89
9.90
Availability: To download the Fan System Assessment Tool and learn more about DOE Qualified Specialists and training opportunities, visit the Industrial Technology Program Web site: www.eere. energy.gov/industry/bestpractices.
System Resistance: The fan operates at a point where the system resistance curve and the fan curve intersects. The system resistance has a major role in determining the performance and efficiency of a fan. The system resistance also changes depending on the process. For example, the formation of the coatings/erosion of the lining in the ducts, changes the system resistance marginally. In some cases, the change of equipment, or duct modifications, drastically shift the operating point, resulting in lower efficiency. In such cases, to maintain the efficiency as before, the fan has to be changed. Hence, the system resistance has to be periodically checked, more so when modifications are introduced and action taken accordingly, for efficient operation of the fan.
9.91
Fan Maintenance: Regular maintenance of fans is important to maintain their performance levels. Maintenance activities include: Periodic inspection of all system components Bearing lubrication and replacement Belt tightening and replacement Motor repair or replacement Fan cleaning Fan Control: Normally, an installed fan operates at a constant speed. But some situations may require a speed change; for example, more airflow may be needed from the fan when a new run of duct is added, or less airflow may be needed if the fan is oversized. There are several ways to reduce or control the airflow of fans. These are summarized in Table 9.8.1.
Table 9.8.1. Fan-flow control comparison (adapted from DOE 2003)
Type of Fan Flow Control Pulley change: reduces the motor/drive pulley size
Disadvantages Fan must be able to handle capacity change Fan must be driven by V-belt system or motor Provide a limited amount of adjustment Reduce the flow but not the energy consumption Higher operating and maintenance costs Less efficient at airflows lower than 80% of full flow
Dampers: reduce the amount of flow and increases the upstream pressure, which reduces fan output
Inlet guide vanes: create swirls in the fan direction thereby lessening the angle between incoming air and fan blades, and thus lowering fan load, pressure and airflow Variable Speed Drive (VSD): reducing the speed of motor of the fan to meet reduced flow requirements Mechanical VSDs: hydraulic clutches, fluid couplings, and adjustable belts and pulleys Electrical VSDs: eddy current clutches, wound rotor motor controllers, and variable frequency drives (VFDs: change motors rotational speed by adjusting electrical frequency of power supplied)
Improve fan efficiency because both fan load and delivered airflow are reduced Cost-effective at airflows between 80-100% of full flow Most improved and efficient flow control Allow fan speed adjustments over a continuous range For VFDs specifically: Effective and easy flow control Improve fan operating efficiency over a wide range of operating conditions Can be retrofitted to existing motors compactness No fouling problems Reduce energy losses and costs by lowering overall system flow
Mechanical VSDs can have fouling problems Investment costs can be a barrier
9.92
9.93
X X X
Observe actuator/ linkage control Check fan blades Filters Check for air quality anomalies
X X X X
X X X X
9.94
9.8.12 References
American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). 1992. ASHRAE HVAC Systems and Equipment, I-P ed, ASHRAE Handbook, Atlanta, Georgia. Bodman, G.R. and D.P. Shelton. July 2, 2001. Ventilation Fans: Types and Sizes. Institute of Agriculture and Natural Resources, University of Nebraska Cooperative Extension, University of Nebraska, May 1995 [Online report]. Available URL: http://www.ianr.unl.edu/pubs/farmbuildings/ g1243.htm. Reprinted with permission of the Institute of Agriculture and Natural Resources, University of Nebraska. Confederation of Indian Industry. August 2, 2001. Reduction of Gasifier Air Blower Speed. Energy Efficiency, Green Business Centre. Reprinted with permission of the Confederation of Indian Industry.
Residential/Efficiency.htm.
EPCOR. August 17, 2001. Cooling with Fans [Online]. Available URL: http://www.epcor-group.com/ Reprinted with permission of EPCOR.
General Services Administration. 1995. Public Buildings Maintenance Guides and Time Standards. Publication 5850, Public Building Service, Office of Real Property Management and Safety. North Carolina State University. August 16, 2001. Confined Space Ventilation. Appendix D, Health & Safety Manual, Environmental Health & Safety Center [Online report]. Available URL: http://www2.ncsu.edu/ncsu/ehs/www99/right/handsMan/confined/Appx-D.pdf. Reprinted with permission of North Carolina State University. UNEP, 2006. Energy Efficiency Guide for Industry, 2006. United Nations Environmental Program. Washington D.C. U.S. Department of Energy (U.S. DOE) 2003. Improving Fan System Performance A Sourcebook for Industry. Available on-line at URL: www1.eere.energy.gov/industry/bestpractices/pdfs/fan_sourcebook.pdf.
9.95
9.9 Pumps
9.9.1 Introduction
Keeping pumps operating successfully for long periods of time requires careful pump design selection, proper installation, careful operation, the ability to observe changes in performance over time, and in the event of a failure, the capacity to thoroughly investigate the cause of the failure and take measures to prevent the problem from recurring. Pumps that are properly sized and dynamically balanced, that sit on stable foundations with good shaft alignment and with proper lubrication, that operators start, run, and stop carefully, and that maintenance personnel observe for the appearance of unhealthy trends which could begin acting on and causing damage to, usually never experience a catastrophic failure (Piotrowski 2001).
9.96
For purposes of this guide, positive displacement pumps (Figure 9.9.3) are classified into two general categories and then subdivided into four categories each:
9.97
Multiple Rotor (Pump World 2001d) - Gear Fluid is carried between gear teeth and is expelled by the meshing of the gears that cooperate to provide continuous sealing between the pump inlet and outlet. - Lobe Fluid is carried between rotor lobes that cooperate to provide continuous sealing between the pump inlet and outlet. - Circumferential Piston Fluid is carried in spaces between piston surfaces not requiring contacts between rotor surfaces. 9.98
Multiple Screw Fluid is carried between rotor screw threads as they mesh.
O&M Best Practices Guide, Release 3.0
Relief Valves (Pump World 2001e) Note: A relief valve (Figure 9.9.5) on the discharge side of a positive displacement pump is an absolute must for safety! - Internal Relief Valve Pump manufacturers normally have an option to supply an internal relief valve. These relief valves will temporarily relieve the pressure on the discharge side of a pump operating against a closed valve. They are normally not full ported, i.e., cannot bypass all the flow produced by the pump. These internal relief valves should be used for pump protection against a temporary closing of a valve. - External Relief Valve An external relief valve (RV) installed in the discharge line with a return line back to the supply tank is highly recommended to provide complete protection against an unexpected over pressure situation.
- When operating pump: Do not operate below minimum rated flow, or with suction/discharge valves closed. Do not open vent or drain valves, or remove plugs while system is pressurized. Maintenance safety - Always lock out power. - Ensure pump is isolated from system and pressure is relieved before any disassembly of pump, removal of plugs, or disconnecting piping. - Pump and components are heavy. Failure to properly lift and support equipment could result in serious injury. - Observe proper decontamination procedures. Know and follow company safety regulations. - Never apply heat to remove impeller.
The following are measures that can improve pump efficiency: (OIT 1995)
Shut down unnecessary pumps. Restore internal clearances if performance has changed. Trim or change impellers if head is larger than necessary. Control by throttle instead of running wide-open or bypassing flow. Replace oversized pumps. Use multiple pumps instead of one large one.
Proper maintenance is vital to achieving Use a small booster pump. top pump efficiency expected life. Additionally, Change the speed of a pump for the most efficient becausepumps are a vital part of many HVAC match of horsepower requirements with output. and process applications, their efficiency directly affects the efficiency of other system components. For example, an improperly sized pump can impact critical flow rates to equipment whose efficiency is based on these flow ratesa chiller is a good example of this.
The heart beats an average of 75 times per minute, or about 4,500 times per hour. While the body is resting, the heart pumps 2.5 ounces of blood per beat. This amount does not seem like much, but it sums up to almost 5 liters of blood pumped per minute by the heart, or about 7,200 liters per day. The amount of blood delivered by the heart can vary depending upon the bodys need. During periods of great activity, such as exercising, the body demands higher amounts of blood, rich in oxygen and nutrients, increasing the hearts output by nearly five times. O&M Best Practices Guide, Release 3.0
9.102
Pump Selection In selecting a pump, facility managers try to match the system curve supplied by the user with a pump curve that satisfies these needs as closely as possible. The pump operating point is the point where the pump curve and the system resistance curve intersect. However, it is impossible for one operating point to meet all desired operating conditions. For example, when the discharge valve is throttled to control flow, the system resistance curve shifts so does the operating point this to a lessthan efficient point of operation. The efficiency of a pump is affected when the selected pump is oversized. This is because flow of oversized pumps must be controlled with different methods, such as a throttle valve or a by-pass line. These devices provide additional resistance by increasing the friction. As a result the system curve shifts and intersects the pump curve at a different point, a point of lower efficiency. In other words, the pump efficiency is reduced because the output flow is reduced but power consumption is not. Inefficiencies of oversized pumps can be overcome by, for example, the installation of variable speed drives, two-speed drives, operating the pump at a lower rpm, or installing a smaller impeller or trimmed impeller (BEE 2004). Controlling flow rate by speed variation A centrifugal pumps rotating impeller generates head. The impellers peripheral velocity is directly related to shaft rotational speed. Therefore varying the rotational speed has a direct effect on the performance of the pump. The pump performance parameters (flow rate, head, power) will change with varying rotating speeds. To safely control a pump at different speeds it is therefore important to understand the relationships between the two. The equations that explain these relationships are known as the Affinity Laws these are: Flow rate (Q) is directly proportional to the rotating speed Head (H) is proportional to the square of the rotating speed Power (P) is proportional to the cube of the rotating speed As can be seen from the above laws, doubling the rotating speed of the centrifugal pump will increase the power consumption by 8 times. Conversely a small reduction in speed will result in a very large reduction in power consumption. This forms the basis for energy conservation in centrifugal pumps with varying flow requirements. It is relevant to note that flow control by speed regulation is always more efficient than by a control valve. This is because valves reduce the flow, but not the energy consumed by pumps. In addition to energy savings, other benefits could include: Increased bearing life this is because bearings carry the hydraulic forces on the impeller (created by the pressure profile inside the pump casing), which are reduced approximately with the square of speed. For a pump, bearing life is proportional to the seventh power of speed. Vibration and noise are reduced and seal life is increased, provided that the duty point remains
within the allowable operating range.
9.103
Using variable speed drive (VSD) Controlling the pump speed is the most efficient way to control the flow, because when the pumps speed is reduced, the power consumption is also reduced. The most commonly used method to reduce pump speed is Variable Speed Drive (VSD). VSDs allow pump speed adjustments over a continuous range, avoiding the need to jump from speed to speed as with multiple-speed pumps. VSDs control pump speeds use two types of systems: Mechanical VSDs include hydraulic clutches, fluid couplings, and adjustable belts and pulleys. Electrical VSDs include eddy current clutches, wound-rotor motor controllers, and variable
frequency drives (VFDs). VFDs are the most popular and adjust the electrical frequency of the
power supplied to a motor to change the motors rotational speed.
For many systems, VFDs offer a means to improve the pump operating efficiency under different operating conditions. When a VFD reduced the RPM of a pump, the head/flow and power curves move down and to the left, and the efficiency curve also shifts to the left. The major advantages of VSD application in addition to energy saving are (DOE, 2004): Improved process control because VSDs can correct small variations in flow more quickly. Improved system reliability because wear of pumps, bearings and seals is reduced. Reduction of capital & maintenance cost because control valves, by-pass lines, and conventional starters are no longer needed. Soft starter capability: VSDs allow the motor the motor to have a lower startup current. Eliminating flow control valve Another method to control the flow by closing or opening the discharge valve (this is also known as throttling the valves). While this method reduces the flow, it does not reduce the power consumed, as the total head (static head) increases. This method increases vibration and corrosion and thereby increases maintenance costs of pumps and potentially reduces their lifetimes. VSDs are always a better solution from an energy efficiency perspective. Eliminating by-pass control The flow can also be reduced by installing a by-pass control system, in which the discharge of the pump is divided into two flows going into two separate pipelines. One of the pipelines delivers the fluid to the delivery point, while the second pipeline returns the fluid to the source. In other words, part of the fluid is pumped around for no reason, and thus is energy inefficient. Because of this inefficiency, this option should therefore be avoided. Impeller trimming Changing the impeller diameter gives a proportional change in the impellers peripheral velocity. Similar to the affinity laws, the following equations apply to the impeller diameter: Flow rate (Q) is proportional to the diameter Head (H) is proportional to the square of the diameter Power (P) is proportional to the cube of the diameter
9.104 O&M Best Practices Guide, Release 3.0
Changing the impeller diameter is an energy efficient way to control the pump flow rate. However, for this option, the following should be considered: This option cannot be used where varying flow patterns exist. The impeller should not be trimmed more than 25% of the original impeller size, otherwise it
leads to vibration due to cavitation and therefore decrease the pump efficiency.
The balance of the pump has to been maintained, i.e. the impeller trimming should be the same on all sides. Changing the impeller itself is a better option than trimming the impeller, but is also more expensive and sometimes the next smaller impeller is too small.
9.105
Results. In addition to the annual 17,650 kWh of electricity savings from modifying the pump unit, significant energy savings also resulted from changes made to other energy use sources in the station (Figure9.9.6). Annual energy consumption of the active level control (7,300 kWh/year) and the cooling water pumps (1,750 kWh/year) was entirely eliminated. In all, over 26,000 kWh is being saved annually, a reduction of almost 38%, resulting in $2,200 in annual energy savings.
This project also produced maintenance savings of $3,600. Maintenance staff no longer needs to replace two mechanical seals each year. Other benefits of the project savings include extended equipment life due to reduced starting and stopping of the equipment, increased system capacity, and decreased noise. Most of the same measures can be utilized at the towns other pumping stations, as well. The total annual savings from the project, due to lower energy costs as well as reduced maintenance and supplies, is $5,800 (Figure 9.9.7), which is roughly half of the total retrofit cost of $11,000. Lessons Learned. Several key conclusions from Trumbulls experience are relevant for virtually any pumping systems project:
Proper pump selection and careful attention to equipment operating schedules can yield
substantial energy savings.
In systems with static head, stepping of pump sizes for variable flow rate applications can decrease energy consumption. A systems approach can identify energy and cost savings opportunities beyond the pumps
themselves.
9.106
X X
X X X X
9.107
9.9.12 References
Bureau of Energy Efficiency, Ministry of Power, India. 2004. Pumps and Pumping Systems. In: Energy Efficiency in Electrical Utilities, Chapter 6. General Services Administration. 1995. Public Buildings Maintenance Guides and Time Standards. Publication 5850, Public Building Service, Office of Real Property Management and Safety. OIT. 1995. Modern Industrial Assessments: A Training Manual. Industrial Assessment Manual from the Office of Productivity and Energy Assessment at the State University of New Jersey, Rutgers, for the U.S. Department of Energy Office of Industrial Technology. Piotrowski, J. April 2, 2001. Pro-Active Maintenance for Pumps. Archives, February 2001, Pump-Zone.com [Report online]. Available URL: http://www.pump-zone.com. Reprinted with permission of Pump & Systems Magazine. Pompe Spec Incorporated. July 13, 2001. Safety Tips. Resources [Online]. Available URL: Reprinted with permission of Pompe Spec Incorporated.
http://www.pompespec.com/frameset_e.html?ressources_e.html~bodypompespec.
Pump World [Online]. Available URL: http://www.pumpworld.com/contents.htm. Reprinted with permission of the Pump World. U.S. Department of Energy (DOE). May 4, 2001. Case Study: Pump Optimization for Sewage Pumping Station. Federal Management Energy Program [Online report]. Available URL: http://www.eere. energy.gov/femp/technologies/eep_centrifugal_pump.cfm. Viking Pump, Incorporated. May 25, 2001. Rotary Pump Family Tree. PumpSchool.com [Online]. Available URL: http://www.pumpschool.com/intro/pdtree.htm. Reprinted with permission of Viking Pump, Incorporated. U.S. Department of Energy (DOE) 2001. Office of Industrial Technologies. Pump Life Cycle Costs: A guide to LCC analysis for pumping systems. DOE/GO-102001-1190. 2001. Available URL: http://www1.eere.energy.gov/industry/bestpractices/techpubs_motors.html. U.S. Department of Energy (US DOE) 2004. Office of Industrial Technologies. Variable Speed Pumping A Guide to Successful Applications. Executive Summary. 2004. http://www1.eere.energy.gov/
industry/bestpractices/techpubs_motors.html.
9.108
9.10 Motors
9.10.1 Introduction
Motor systems consume about 70% of all the electric energy used in the manufacturing sector of the United States. To date, most public and private programs to improve motor system energy efficiency have focused on the motor component. This is primarily due to the complexity associated with motor-driven equipment and the system as a whole. The electric motor itself, however, is only the core component of a much broader system of electrical and mechanical equipment that provides a service (e.g., refrigeration, compression, or fluid movement). Numerous studies have shown that opportunities for efficiency improvement and performance optimization are actually much greater in the other components of the system-the controller, the mechanical system coupling, the driven equipment, and the interaction with the process operation. Despite these significant system-level opportunities, most efficiency improvement activities or programs have focused on the motor component or other individual components (Nadel et al. 2001).
9.10.2.2 AC Motors
(Naves 2001b) As in the DC motor case, an AC motor (Figure 9.10.2) has a current passed through the coil, generating a torque on the coil. The design of an AC motor is considerably more involved than the design of a DC motor. The magnetic field is produced by an electromagnet powered by the same AC voltage as the motor coil. The coils that produce the magnetic field are traditionally called the field coils while the coils and the solid core that rotates is called the armature.
O&M Best Practices Guide, Release 3.0
Reprinted with permission of Dr. R. Naves, Department of Physics and Astronomy, Georgia State University.
9.109
Induction motor (VPISU 2001) The induction motor is a three-phase AC motor and is the most widely used machine. Its characteristic features are: - Simple and rugged construction. - Low cost and minimum maintenance. - High reliability and sufficiently high efficiency. - Needs no extra starting motor and need not be synchronized.
Reprinted with permission of Dr. R. Naves, Department of Physics and Astronomy, Georgia State University.
An induction motor operates on the principle of induction. The rotor receives power due to induction from stator rather than direct conduction of electrical power. When a three-phase voltage is applied to the stator winding, a rotating magnetic field of constant magnitude is produced. This rotating field is produced by the contributions of space-displaced phase windings carrying appropriate time displaced currents. The rotating field induces an electromotive force (emf). Synchronous motor (Apogee Interactive 2001b) The most obvious characteristic of a synchronous motor is its strict synchronism with the power line frequency. The reason the industrial user is likely to prefer a synchronous motor is its higher efficiency and the opportunity for the user to adjust the motors power factor. A specially designed motor controller performs these operations in the proper sequence and at the proper times during the starting process.
9.110
Armature When current goes through the armature, it becomes an electromagnet. The armature, cylindrical in shape, is linked to a drive shaft in order to drive the load. For the case of a small DC motor, the armature rotates in the magnetic field established by the poles, until the north and south poles of the magnets change location with respect to the armature. Once this happens, the current is reversed to switch the south and north poles of the armature. Commutator This component is found mainly in DC motors. Its purpose is to overturn the direction of the electric current in the armature. The commutator also aids in the transmission of current between the armature and the power source.
9.10.3.2 AC Motor
Rotor - Induction motor (VPISU 2001) Two types of rotors are used in induction motors: squirrel-cage rotor and wound rotor. (Figure 9.10.4) A squirrel-cage rotor consists of thick conducting bars embedded in parallel slots. These bars are short-circuited at both ends by means of short-circuiting rings. A wound rotor has three-phase, Reprinted with permission of Apogee Interactive. double-layer, distributed winding. It is wound for as many poles as the stator. Figure 9.10.3. Parts of a direct current motor The three phases are wired internally and the other ends are connected to slip-rings mounted on a shaft with brushes resting on them. - Synchronous motor The main difference between the synchronous motor and the induction motor is that the rotor of the synchronous motor travels at the same speed as the rotating magnetic field. This is possible because the magnetic field of the rotor is no longer induced. The rotor either has permanent magnets or DC-excited currents, which are forced to lock into a certain position when confronted with another magnetic field. Stator (VPISU 2001) - Induction motor The stator is made up of a number of stampings with slots to carry three-phase windings. It is wound for a definite number of poles. The windings are geometrically spaced 120 degrees apart. Synchronous motor The stator produces a rotating magnetic field that is proportional to the frequency supplied.
Figure 9.10.4. Parts of an alternating current motor O&M Best Practices Guide, Release 3.0 9.111
9.112
The best safeguard against thermal damage is avoiding conditions that contribute to overheating. These include dirt, under and over-voltage, voltage unbalance, harmonics, high ambient temperature, poor ventilation, and overload operation (even within the service factor). Bearing failures account for nearly one-half of all motor failures. If not detected in time, the failing bearing can cause overheating and damage insulation, or can fail catastrophically and do irreparable mechanical damage to the motor. Preventative and predictive maintenance programs for motors are effective practices in manufacturing plants. These maintenance procedures involve a sequence of steps plant personnel use to prolong motor life or foresee a motor failure. The technicians use a series of diagnostics such as motor temperature and motor vibration as key pieces of information in learning about the motors. One way a technician can use these diagnostics is to compare the vibration signature found in the motor with the failure mode to determine the cause of the failure. Often failures occur well before the expected design life span of the motor and studies have shown that mechanical failures are the prime cause of premature electrical failures. Preventative maintenance takes steps to improve motor performance and to extend its life. Common preventative tasks include routine lubrication, allowing adequate ventilation, and ensuring the motor is not undergoing any type of unbalanced voltage situation. The goal of predictive maintenance programs is to reduce maintenance costs by detecting problems early, which allows for better maintenance planning and less unexpected failures. Predictive maintenance programs for motors observe the temperatures, vibrations, and other data to determine a time for an overhaul or replacement of the motor (Barnish et al. 2001). Consult each motors instructions for maintenance guidelines. Motors are not all the same. Becareful not to think that what is good for one is good for all. For example, some motors require a periodic greasing of the bearings and some do not (Operators and Consulting Services Incorporated 2001).
9.113
9.114
MotorMaster+ allows users to create or import an inventory of in-plant operating and spare motors. Motor load, efficiency at the load point, annual energy use, and annual operating costs can be determined after taking field measurements. The software quickly identifies inefficient or oversized facility motors and computes the savings that can be achieved by replacing older, standard efficiency motors with premium efficiency models. The software runs on local or wide-area networks for access by multiple users. Some of MotorMaster+ features include: Expanded list of more than 17,000 motors from 14 manufacturers, including National Electrical Manufacturers Association (NEMA) Premium efficiency medium-voltage (>600 volt) motors. Improved predictive maintenance testingfacilitates rapid data entry, sorting by condition, and rewind/replace recommendations. Technical data to help optimize drive systems, such as data on motor part-load efficiency and
power factor; full-load speed; and locked-rotor, breakdown, and full-load torque.
Motor purchasing information, including list prices, warranty periods, catalog numbers, motor
weights, and manufacturer addresses.
Capability to calculate energy savings, dollar savings, simple payback, cash flows, and the aftertaxes rate of return-on-investment for energy programstaking into account such variables as load factor, motor efficiency, purchase price, energy costs, hours of operation, and utility rebates. Availability: To download the MotorMaster+ and learn more about DOE Qualified Specialists and training opportunities, visit the Industrial Technology Program Web site: www1.eere.energy.gov/ industry/bestpractices.
9.115
Sizing to variable load. Industrial motors frequently operate under varying load conditions due to process requirements. A common practice in this situation is to select a motor based on the highest anticipated load. But this makes the motor more expensive as the motor would operate at full capacity for short periods only, and it carries the risk of motor under-loading. An alternative is to select the motor rating based on the load duration curve of a particular application. This means that the selected motor rating is slightly lower than the highest anticipated load and would occasionally overload for a short period of time. This is possible as manufacturers design motors with a service factor (usually 15% above the rated load) to ensure that running motors above the rated load once in a while will not cause significant damage. The biggest risk is overheating of the motor, which adversely affects the motor life and efficiency and increases operating costs. A criteria in selecting the motor rating is therefore that the weighted average temperature rise over the actual operating cycle should not be greater than the temperature rise under continuous full-load operation (100%). Overheating can occur with: Extreme load changes, such as frequent starts / stops, or high initial loads Frequent and/or long periods of overloading Limited ability for the motor to cool down, for example at high altitudes, in hot environments or when motors are enclosed or dirty Improving power quality. Motor performance is affected considerably by the quality of input power, which is determined by the actual volts and frequency compared to rated values. Fluctuation in voltage and frequency much larger than the accepted values has detrimental impacts on motor performance. Voltage unbalance can be even more detrimental to motor performance and occurs when the voltages in the three phases of a three-phase motor are not equal. This is usually caused by the supply different voltages to each of the three phases. It can also result from the use of different cable sizes in the distribution system. The voltage of each phase in a three-phase system should be of equal magnitude, symmetrical, and separated by 120. Phase balance should be within 1% to avoid de-rating of the motor and voiding of manufacturers warranties. Several factors can affect voltage balance: single-phase loads on any one phase, different cable sizing, or faulty circuits. An unbalanced system increases distribution system losses and reduces motor efficiency. Voltage unbalance can be minimized by: Balancing any single phase loads equally among all the three phases Segregating any single phase loads which disturb the load balance and feed them from a separate line/transformer Improving maintenance. Most motor cores are manufactured from silicon steel or de-carbonized cold-rolled steel, the electrical properties of which do not change measurably with age. However, poor maintenance can cause deterioration in motor efficiency over time and lead to unreliable operation. For example, improper lubrication can cause increased friction in both the motor and associated drive transmission equipment. Resistance losses in the motor, which rise with temperature, would increase.
9.116 O&M Best Practices Guide, Release 3.0
Ambient conditions can also have a detrimental effect on motor performance. For example, extreme temperatures, high dust loading, corrosive atmosphere, and humidity can impair insulation properties; mechanical stresses due to load cycling can lead to misalignment. Appropriate maintenance is needed to maintain motor performance. A checklist of good maintenance practices would include: Inspect motors regularly for wear in bearings and housings (to reduce frictional losses) and for
dirt/dust in motor ventilating ducts (to ensure proper heat dissipation.
Check load conditions to ensure that the motor is not over or under loaded. A change in motor load from the last test indicates a change in the driven load, the cause of which should be understood Lubricate appropriately. Manufacturers generally give recommendations for how and when to lubricate their motors. Inadequate lubrication can cause problems, as noted above. Overlubrication can also create problems, e.g. excess oil or grease from the motor bearings can enter the motor and saturate the motor insulation, causing premature failure or creating a fire risk Check periodically for proper alignment of the motor and the driven equipment. Improper alignment can cause shafts and bearings to wear quickly, resulting in damage to both the motor and the driven equipment Ensure that supply wiring and terminal box are properly sized and installed. Inspect regularly the connections at the motor and starter to be sure that they are clean and tight Provide adequate ventilation and keep motor cooling ducts clean to help dissipate heat to reduce excessive losses. The life of the insulation in the motor would also be longer: for every 10C increase in motor operating temperature over the recommended peak, the time before rewinding would be needed is estimated to be halved. Multi-speed motors. Motors can be wound such that two speeds, in the ratio of 2:1, can be obtained. Motors can also be wound with two separate windings, each giving two operating speeds and thus a total of four speeds. Multi-speed motors can be designed for applications involving constant torque, variable torque, or for constant output power. Multi-speed motors are suitable for applications that require limited speed control (two or four fixed speeds instead of continuously variable speed). These motors tend to be very economical as their efficiency is lower compared to single-speed motors. Variable speed drives (VSDs). VSDs are also called adjustable speed drives and can change the speed of a motor and are available in a range from several kW to 750kW. They are designed to operate standard induction motors and can therefore be easily installed in an existing system. When loads vary, VSDs or two-speed motors can often reduce electrical energy consumption in centrifugal pumping and fan applications by 50% or more. The basic drive consists of the inverter itself which converts the 60Hz incoming power to a variable frequency and variable voltage. The variable frequency will control the motor speed.
9.117
X X
Motor alignment Check mountings Check terminal tightness Cleaning Check bearings Motor condition
X X X X X X
Check for balanced three-phase power Check for overvoltage or undervoltage conditions
X X
9.118
9.10.11 References
Apogee Interactive. July 5, 2001a. Characteristics of Direct Current Motors. Electrical Systems. Reprinted with permission of Apogee Interactive, www.apogee.net. Apogee Interactive. July 5, 2001b. Characteristics of a Synchronous Motor. Electrical Systems Reprinted with permission of Apogee Interactive, www.apogee.net. Barnish, T.J., M.R. Muller, and D.J. Kasten. June 14, 2001. Motor Maintenance: A Survey of Techniques and Results. Presented at the 1997 ACEEE Summer Study on Energy Efficiency in Industry, July 8-11, 1997, Saratoga Springs, New York, Office of Industrial Productivity and Energy Assessment, Confederation of Indian Industry. July 15, 2001. Replacement with Correct Size Combustion Air Blower in Kiln. Case Studies. Reprinted with permission of Confederation of Indian Industry. Nadel, S.R., N. Elliott, M. Shepard, S. Greenberg, G. Katz, and A.T. de Almeida. Forthcoming (2001). Energy-Efficient Motor Systems: A Handbook on Technology, Program, and Policy Opportunities. Second Edition. American Council for an Energy-Efficient Economy. Washington, D.C. Naves, R. July 8, 2001a. DC Motor. Electricity and Magnetism, HyperPhysics, Department of Physics and Astronomy, Georgia State University [Online]. Available URL: http://hyperphysics.phyastr.gsu.edu/hbase/magnetic/motdc.html#c1. Reprinted with permission Dr. R. Naves, Department of Physics and Astronomy, Georgia State University. Naves, R. July 8, 2001b. AC Motor. Electricity and Magnetism, HyperPhysics, Department of Physics and Astronomy, Georgia State University [Online]. Available URL: http://hyperphysics. phy-astr.gsu.edu/hbase/magnetic/motorac.html. Reprinted with permission Dr. R. Naves, Department of Physics and Astronomy, Georgia State University. Operators and Consulting Services Incorporated. May 30, 2001. Electric Motors. Oilfield Machinery Maintenance Online [Online]. Available URL: http://www.oilmachineryforum.com/electric.htm. Reprinted with permission of Operators and Consulting Services Incorporated. The World Book Encyclopedia. 1986. Motors. Volume 13, World Book, Inc. UNEP, 2006. Energy Efficiency Guide for Industry, 2006. United Nations Environmental Program. Washington, D.C. U.S. Department of Energy (DOE). 2001. Greening Federal Facilities: An Energy, Environmental, and Economic Resource Guide for Federal Facility Managers and Designers. 2nd ed., PartV Energy Systems, 5.7 Electric Motors and Drives, Federal Management Energy Program [Online report]. Available URL: http://www.nrel.gov/docs/fy01osti/29267.pdf. U.S. Department of Energy (DOE). 2003. Fact Sheet: Determining Motor Load and Efficiency. Available URL: http://www1.eere.energy.gov/industry/bestpractices/pdfs/10097517.pdf. Virginia Polytechnic Institute and State University and Iowa State University (VPISU). July 14, 2001. Induction Motor, Powerlearn Program funded by the National Science Foundations and the Electric Power Research Institute [Online]. Reprinted with permission of Virginia Polytechnic Institute and State University.
9.119
A plants expense for its compressed air is often thought of only in terms of the cost of the equipment. Energy costs, however, represent as much as 70% of the total expense in producing compressed air. As electricity rates escalate across the nation and the cost of maintenance and repair increases, selecting the most efficient and reliable compressor becomes critical (Kaeser Compressors 2001a).
Figure 9.11.1. Rotary screw compressor 9.120 O&M Best Practices Guide, Release 3.0
Reciprocating compressor A reciprocating compressor (Figure 9.11.2) is made up of a cylinder and a piston. Compression is accomplished by the change in volume as the piston moves toward the top end of the cylinder. This compression may be oil-lubricated or, in some cases, it may require little or no lubrication (oil-free) in the cylinder. The cylinder in the reciprocating machines may be air cooled or water cooled. Water cooling is used on the larger units. This cooling action is very important to increase compressor life and to keep maintenance and repairs low. Multiple stage compressors have a minimum of two pistons. The first compresses the gas to an intermediate pressure. Intercooling of the gas before entering the second stage usually follows the first stage compression. Two stage units allow for more efficient and cooler operating compressors, which increases compressor life.
Rotary Screw Compressor - Helical-lobe rotors The main elements of this type of compressor where two close clearance helical-lobe rotors turn in synchronous mesh. As the rotors revolve, the gas is forced into a decreasing inter-lobe cavity until it reaches the discharge port (Figure 9.11.3). Centrifugal Compressor - Rotating Impeller Imparts velocity to the air, which is converted to pressure.
Pressure regulation devices - Valves, gauges, and other regulating devices should be installed on compressor equipment in such a way that cannot be made inoperative. Air tank safety valves should be set no less than 15 psi or 10% (whichever is greater) above the operating pressure of the compressor but never higher than the maximum allowable working pressure of the air receiver.
Air compressor operation - Air compressor equipment should be operated only by authorized and trained personnel. - The air intake should be from a clean, outside, fresh air source. Screens or filters can be used to clean the air. - Air compressors should never be operated at speeds faster than the manufacturers
recommendation.
- Moving parts, such as compressor flywheels, pulleys, and belts that could be hazardous should be effectively guarded.
9.123
caused by higher than needed pressure is called artificial demand. A system using 520cfm at 110psig inlet pressure will consume only 400cfm at 80psig. The potential power cost savings (520 cfm - 400cfm = 120cfm, resulting in 24 hp, at 10cents/kWh; 8,760 hr/year) is $18,000/ year. Note: Also remember that the leakage rate is significantly reduced at lower pressures, further reducing power costs. The cost of wasted air volume Each cubic feet per meter of air volume wasted can be translated into extra compressor horsepower and is an identifiable cost. As shown by Chart 1, if this waste is recovered, the result will be $750/hp per year in lower energy costs. Select the most efficient demand side The magnitude of the above is solely dependent on the
ability of the compressor control to translate reduced airflow into lower electrical power
consumption.
The chart below shows General Notes on Air Compressors (OIT 1995) the relationship between the Screw air compressors use 40% to 100% of rated power unloaded. full load power required for a compressor at various air Reciprocating air compressors are more efficient, but also more expensive. demands and common control types. It becomes apparent About 90% of energy becomes heat. that the on line-off line control Rule of thumb: roughly 20 hp per 100 cfm at 100 psi. (dual control) is superior to Use low-pressure blowers versus compressed air whenever possible. other controls in translating Second, third, weekend shifts may have low compressed air needs savings in air consumption that could be served by a smaller compressor. intoreal power savings. Outside air is cooler, denser, easier to compress than warm inside air. Looking at our example of Friction can be reduced by using synthetic lubricants. reducing air consumption from Older compressors are driven by older less efficient motors. 520 cfm to 400 cfm (77%), the compressor operating on dual control requires 83% of full load power. That is 12% less energy than when operated on modulation control. If the air consumption drops to 50%, the difference (dual versus modulation) in energy consumption is increased even further, to24%.
9.11.5.2 Waste Heat Recovered from Compressors can be Used for Heating (Kaeser Compressors 2001c)
The heat generated by air compressors can be used effectively within a plant for space heating and/or process water heating. Considerable energy savings result in short payback periods. Process heating Heated water is available from units
equipped with water-cooled oil coolers and after-coolers.
Generally, these units can effectively discharge the water at
temperatures between 130F and 160F.
Space heating Is essentially accomplished by ducting the
heated cooling air from the compressor package to an area
that requires heating. If ductwork is used, be careful not to
exceed the manufacturers maximum back-pressure allowance.
9.124
When space heating is used in the winter, arrangements should be made in the ductwork to return some of the heated air to the compressor room in order to maintain a 60F room temperature. This ensures that the air discharged is at comfortable levels.
almost all system equipment (including the compressor package itself). Increased running time can also lead to additional maintenance requirements and increased unscheduled downtime. Finally, leaks can lead to adding unnecessary compressor capacity. While leakage can come from any part of the system, the most common problem areas are: Couplings, hoses, tubes, and fittings Pressure regulators Open condensate traps and shut-off valves Pipe joints, disconnects, and thread sealants. Leakage rates are a function of the supply pressure and increase with higher system pressures. For compressors that have start/stop or load/unload controls, there is an easy way to estimate the amount of leakage in the system. This method involves starting the compressor when there are no demands on the system (when all the air-operated, end-use equipment is turned off). A number of measurements are taken to determine the average time it takes to load and unload the compressor. The compressor will load and unload because the air leaks will cause the compressor to cycle on and off as the pressure drops from air escaping through the leaks. Total leakage (percentage) can be calculated as follows (DOE 1998): Leakage Percentage (%) = {(T x 100)/(T + t)} where: T = on-loading time in minutes t = off-loading time in minutes Leakage will be expressed in terms of the percentage of compressor capacity lost. The percentage lost to leakage should be less than 10 percent in a well-maintained system. Poorly maintained systems can have losses as high as 20 to 30 percent of air capacity and power.
9.126
Condensate control - Drain fluid traps regularly or automatically. - Drain receiving tanks regularly or automatically. - Service air-drying systems according to manufacturers recommendations.
Probable Cause
Leaks in distribution piping Clogged filter elements Fouled dryer heat exchanger Low pressure at compressor discharge
Remedial Action
Check lines, connections, and valves for leaks; clean or replace filter elements Clean heat exchanger
Low pressure at For systems with modulating load compressor discharge controls, improper adjustment of air capacity control Worn or broken valves Improper air pressure switch setting Water in lines Failed condensate traps Failed or undersized compressed air dryer Liquid oil in air lines Dirt, rust, or scale in air lines Excessive service to load/hour ratio Faulty air/oil separation In the absence of liquid water,normal aging of the air lines System idling too much
Follow manufacturers recommendation for adjustment of control Check valves and repair or replace as required Follow manufacturers recommendations for setting air pressure switch Clean, repair, or replace the trap Repair or replace dryer Check air/oil separation system; change separator element Install filters at point of use For multiple compressor systems, consider sequencing controls to minimize compressor idle time; adjust idle time according to manufacturers recommendations Readjust according to manufacturers recommendations Clean cooler exterior and check inlet filter mats Check water flow, pressure, and quality; clean heat exchanger as needed Check compressor oil level; add oil as required Remove restriction; replace parts as required Improper ventilation to compressor; check with manufacturer to determine maximum operating temperature
Improper pressure switch setting Elevated compressor temperature Restricted airflow Restricted water flow Low oil level Restricted oil flow Excessive ambient temperatures
9.127
Keep air inlet filters clean. Keep motor belts tight. Minimize system leaks.
For well-rounded orifices, multiply the values by 0.97, and for sharp-edged orifices, multiply the values by 0.61 (DOE 2000).
Estimated Annual Energy Savings. The annual energy savings, which could be realized by fixing a compressed air leak, can be estimated as follows: where N = number of leaks, no units LR = leakage rate, cfm (from the table above) EU = compressor energy use, kW/cfm H = annual hours of operation, hours C = orifice edge coefficient, no units Estimated Annual Cost Savings. The annual cost savings, which could be realized by fixing a compressed air leak, can be estimated as follows:
9.129
It should be noted that this cost savings calculation doesnt account for an electric peak demand reduction. If the facility has a peak demand charge, and the compressor operates everyday with an operational schedule that is coincident with the facilitys peak demand, then this estimate slightly underestimates the cost savings. Compressed Air Leaks Energy Savings and Economics Example Synopsis A compressed air system audit reveals 5 air leaks, all with an estimated orifice diameter of 1/16 of an inch. The leaks are located in a line pressurized to 100 psig. The energy use of the compressor is 18kW/100cfm, and is operated 8,760hrs per year. The electrical rate is approximately $0.10 per kWh. (Assumed sharp edged orifice, multiplier equals 0.61) The annual energy savings can be estimated as:
Compressed Air Systems Rules of Thumb (EPA 2003) Compressed Air Rule 1. Efficiency improvements can reduce compressed air system energy use by 20% to 50%. Compressed Air Rule 2. Efficiency improvements to compressed air systems can save approximately one-half percent of a facilitys total energy use. Compressed Air Rule 3. Repairing air leaks can reduce compressed air system energy use by 30% or more. Compressed Air Rule 4. Repairing air leaks can reduce a facilitys total energy use by about onehalf percent, with an average simple payback of 3 months. Compressed Air Rule 5. It takes approximately 2.5 to 5.0 kWh to compress 1,000 ft3 of air to 100 psi. Each psi reduction in compressed air loss from the distribution system (at 100 psi), reduces a compressors energy use by more than one-half percent.
9.130
In the absence of calculating the cost of a compressed air leak, Table 9.11.5 can be used as a rough cost estimate for compressed air leakage cost (DOE 2003)
Table 9.11.5. Compressed air leaks cost per year assuming $0.05/kWh Size (in.) 1/16 1/8 1/4 Cost Per Year ($/yr) $523 $2,095 $8,382
9.131
The study identified eight major leaks ranging in size from 1/16 to 1/8 inches in diameter. The calculated total annual cost of these leaks was $5,730. Correcting the leaks in this system involved the following: Replacement of couplings and/r hoses. Replacement of seals around filters. Repairing breaks in compressed-air lines. The total cost of the repairs was $460. Thus, the cost savings of $5,730 would pay for the implementation cost of $460 in about a month.
X X X X X X X X X X X
X X
9.132
Chiller Checklist (contd) Description System oil Comments Depending on use and compressor size, develop periodic oil sampling to monitor moisture, particulate levels, and other contamination. Replace oil as required. Inspect all couplings for proper function and alignment Check all seals for leakage or wear Replace particulate and lubricant removal elements when pressure drop exceeds 2-3 psid Check and secure all compressor mountings Maintenance Frequency Daily Weekly Monthly X Annually
X X X X
9.11.12 References
DOE. 1998. Improving Compressed Air System Performance: A Sourcebook for Industry. Industrial Technologies Program, U.S. Department of Energy, Washington, D.C. DOE. 2003. Improving Compressed Air System Performance. DOE/GO-102003-1822, Industrial Technologies Program, U.S. Department of Energy, Washington D.C. Dyer, D.F. and G. Maples. 1992. Electrical Efficiency Improvement. Energy Efficiency Institute, Auburn. EPA. 2003. Wise Rules for Industrial Energy Efficiency A Tool Kit For Estimating Energy Savings and Greenhouse Gas Emissions Reductions. EPA 231-R-98-014, U.S. Environmental Protection Agency, Washington, D.C. FEMP 2008. Federal Energy Management Program - Water Best Management Practices. Available on line at URL: http://www1.eere.energy.gov/femp/program/waterefficiency_bmp.html. Kaeser Compressors, Inc. July 29, 2001a. Getting the Most for Your Money: Types of Compressors. Air Compressor Guide [Online Report]. Available URL: http://www.maintenanceresources.com/ ReferenceLibrary/AirCompressors/kaeserpage1.htm. Kaeser Compressors, Inc. July 29, 2001b. Evaluating Compressor Efficiency. Air Compressor Guide [Online Report]. Available URL: http://www.maintenanceresources.com/ReferenceLibrary/AirCompressors/ kaeserpage7.htm. Kaeser Compressors, Inc. July 29, 2001c. Waste Heat Recovery and the Importance of Maintenance. Air Compressor Guide [Online Report]. Available URL: http://www.maintenanceresources.com/ ReferenceLibrary/AirCompressors/kaeserpage9.htm.
9.133
Kaeser Compressors, Inc. July 29, 2001d. Getting the Most for Your Money: Troubleshooting. Air Compressor Guide [Online Report]. Available URL: http://www.maintenanceresources.com/ ReferenceLibrary/AirCompressors/kaeserpage5.htm. Oil Machinery Maintenance Online. July 16, 2001. Air Compressors [Online]. Available URL: http://www.oilmachineryforum.com/air.htm. OIT. 1995. Modern Industrial Assessments: A Training Manual. Industrial Assessment Manual from the Office of Productivity and Energy Assessment at the State University of New Jersey, Rutgers, for the U.S. Department of Energy Office of Industrial Technology. University of Florida Environmental Health and Safety (UFEHS). July 26, 2001. Compressed Air Safety: General safety requirements for compressed air [Online]. Available URL: http://www.ehs.ufl.edu/ General/Shop/comp_air.htm. UNEP, 2006. Energy Efficiency Guide for Industry, 2006. United Nations Environmental Program. Washington, D.C.
9.134
9.12 Lighting
9.12.1 Introduction
Recent studies reveal that over 20% of the nations electricity consumption is related to various types of lighting products and systems. Advanced energy saving technologies are readily available to reduce both the connected load and energy consumption, but are only effective if they are properly installed, calibrated, and maintained. Improvements in lighting efficiencies are so rapid that it can be cost-effective to implement upgrades, retrofits or redesigns to lighting systems that are only 5 to 10years old. In addition to everyday maintenance and operation of lighting systems, this section discusses the important issues of commissioning and regular reevaluation of system components with a view toward upgrades.
9.135
Fluorescent lamps generate their light by using electricity to excite a conductive vapor of mercury and an inert gas. The resultant ultraviolet light strikes a phosphor coating on the inside of the tube, causing it to glow. The elements used in the phosphor coating control the lamps color. T12 lamps Linear fluorescent lamps with a 1-1/2 inch diameter (12/8 of an inch). They are now considered obsolete for most new applications. These were the standard fluorescent lamps until T8lamps came on the market in the 1980s.
Disadvantages:
Require a compatible ballast Dimming requires a more expensive ballast Temperatures can affect start-up, lumen output, and lamp life Not a point source if narrow beam distribution is required
Appropriate Uses:
Fluorescent and compact fluorescent lamps are appropriate for
most of the applications that Federal facilities managers encounter T8 lamps Linear fluorescent in their buildings lamps with a 1inch diameter (8/8 of an inch). These are the workhorse of the commercial lighting industry and have become the standard for offices and general applications. Since they are 22% more efficient than T12s, it is generally always costeffective to retrofit or replace fixtures that use T12 lamps in existing applications even before the existing T12 lamps burn out. The rare exception might be individual fixtures that are rarely used. However, it will be more efficient to replace or upgrade these at the same time to avoid costly individual replacements at a later date. T8 lamps use the same socket as T12, but not the same ballast. There is a wide range of T8design options and good color rendition. The most commonly used T8 lamp is 4-feet-long and 32-watts (F32T8).
High performance or premium T8 lamps High performance T8s are marketed under the tradenames Ultra (GE), Advantage (Philips), or Super T8 (Sylvania). These T8 lamps provide higher efficacy, higher maintained lumens, and are available in extended life versions with a 20% increase in lamp life. The improved performance is achieved in different ways by different products. Some products have reduced wattages (28 to 30 watts) while achieving the same lumen output as a standard T8. Others have increased lumen output (3,100 lumens) without increasing the wattage. The increased lumen output results in a brighter lamp and potentially more glare. This can be prevented by using the lower wattage version, or by coupling a 3,100 lumen lamp with a reduced output ballast (.77 BF). Premium T8s have a higher initial cost, but the increased energy efficiency and life make them the recommended light source for most commercial fluorescent installations including Federal projects.
9.136
T5 lamps Linear fluorescent lamps with a diameter of 5/8 of an inch. These cannot replace T8 lamps because they have different characteristics and different lengths (metric), socket configurations and ballasts. T5s are smaller lamps than T8s, but have similar efficacy (lumens per watts). Their smaller diameter allows for shallower fixtures and greater reflector control, but also increases the brightness, limiting their use to heavily shielded or indirect fixtures. T5HO (high output) T5 lamps with approximately the same maintained lumens as two standard T8 lamps but less efficient, with about 7% to 10% fewer lumens per watt. This development allows the designer to potentially reduce the number of fixtures, lamps, and ballasts in an application, making it less expensive to maintain. However, the intense brightness of T5HOs limits their use to primarily indirect luminaires to avoid glare. Also, using one-lamp rather than two-lamp luminaires eliminates the potential for two-level switching. Analysis is required to demonstrate the benefits of using T5HO lamps to offset their lower efficacy and highercost. Compact fluorescent lamps (CFLs) Fluorescent lamps with a single base and bent-tube construction. Originally designed for the retrofitting of standard incandescents, the first CFLs had a screwtype base. While screw base lamps are still available, commercial applications typically use lamps with a 4-pin base. This prevents the future replacement of a screw-based CFL with a much less efficient incandescent lamp. CFL lamps have a wide range of sizes and attractive colors, and can be used in most Federal applications that formerly used incandescent.
Disadvantages:
Require a compatible ballast Dimming requires a more expensive ballast
Temperatures can affect start-up, lumen output, High Intensity Discharge (HID) lamps and lamp life also use a gas-filled tube to generate light, Not a point source if narrow beam distribution is but use an arc current and vaporized metals required at relatively high temperatures and pressures. There are two main types in current use metal halide (MH) and high-pressure sodium (HPS) and their characteristics are determined by the gas. MH provides a white light with a CRI of 65-95, while HPS emits a yellowish light with a CRI of 22 to 65. Historically, HID lamps were relegated to outdoor or service areas, but advances in color, configurations, and efficacy have made them more attractive for commercial and interior use.
9.137
Electrodeless lamps (also called induction lamps) most commonly use radio frequency to ionize mercury vapor at low-pressures, resulting in exciting the phosphors inside the envelope to create a glow, similar to fluorescent technology. The three major lamp manufacturers each produce a distinctive lamp design, the small reflector Genura lamp by GE, the globe-shaped QL by Philips, and the high-output donut-shaped Icetron by Sylvania. Incandescent/Halogen lamps generate their light by heating a tungsten filament until it glows, in the presence of an inert gas such as argon or nitrogen. A halogen lamp is a form of incandescent lamp that introduces traces of halogen gas and a quartz envelope to burn hotter and prolong the filament life. Consequently, they are whiter (3000K rather than 2700K) and are slightly more energy efficient than standard incandescents. Halogen should be used in lieu of standard incandescent, and low voltage should be considered for the tighter, more focused beam. However, whenever possible, the use of more efficient CFL or ceramic metal halide sources should be explored. Since incandescent/halogen lamp types are very inefficient (roughly five times less efficient than fluorescent), they should be used sparingly, or the project will not meet the energy code. See the suggested uses below. Light Emitting Diodes (LEDs) are made of an advanced semi-conductor material that emits visible light when current passes through it. Different conductor materials are used, each emitting a distinctive wavelength of light. LEDs come in red, amber, blue, green, and a cool white. LEDs are beginning to see extensive use in a variety of applications including street/ parking lot lighting, supermarket refrigerated display case lighting, and other display lighting applications.
Power Factor (PF) Not lower than 0.90 Total Harmonic Distortion (THD) Not higher than 20% Minimum Starting Temperature appropriate for application Voltage requirements matching supply voltage, or multi-voltage taps Maximum distance between lamp and remotely located ballast check with manufacturer.
9.139
Disadvantages:
Controls must be very reliable and predictable for user acceptance May require expertise and/or training of maintenance personnel Commissioning is required and adjustments may be necessary when layouts change Moderate to high initial cost ($0.20/ft2 for scheduling, higher for daylighting)
Appropriate Uses:
Dimming of electric lighting to support a daylighting strategy Rooms with periods of no occupancy during the day (for occupancy sensors) or have regular operating hours (time clocks) Support spaces and outdoor areas with predictable needs
Occupancy Sensors. Occupancy sensors turn off the lights when they detect that no occupants are present. The occupancy sensor includes a motion sensor, a control unit, and a relay for switching the lights. The sensor and control unit are connected to the luminaire by low voltage wiring, with a transformer stepping down the current. There are three commonly used types of occupancy sensors, defined by how they detect motion: ultrasonic, passive infrared and dualtechnology. Ultrasonic sensors (US) utilize a quartz crystal that emits high frequency ultrasonic waves throughout the room. Shifts to the frequency of the wave (called Doppler effect) indicate that there is motion/occupancy in the space. US cover the area in a continuous manner, and there are no blind spots in the coverage, e.g., a desk behind a partition. While this makes them effective at detecting occupancy, it also makes them more vulnerable to false-on readings caused by traffic in adjacent corridors and air currents. Therefore, they can be most effectively used in combination with manual-on switches (see below), particularly in daylighted spaces. Manual-on prevents false-ons and saves energy by avoiding unnecessary automatic activation when daylight or spill-light is sufficient for theactivity.
Figure 9.12.2. Wall-box occupancy sensor uses hidden internal dip-switches to set manual-on, auto-off.
9.141
Disadvantages:
Lamps have a warm-up period before reaching full output/color If power is interrupted, lamps must cool off before restriking (hence unreliable dimming and unacceptability for emergency lighting). Some HPS lamps are available with instant restrike. Inappropriate for many control strategies like daylight harvesting, occupancy sensors, or frequent switching.
Appropriate Uses:
Metal halide lamps come in a wide range of shapes and colors, and are suitable for most lighting applications where continuous operation is required. Ceramic metal halide technology provides colors in the 80 to 98CRI range with a warm color temperature of 3000K. Metal halide PAR and small tubular lamps provide an energy-efficient substitute for many types incandescent/ halogen reflector and tubular lamps High-pressure sodium (HPS) lamps are most often used in roadway and other outdoor applications. Lamp life is very long (30,000+ hours), but the CRI is low (about 22 to 30). Improved whiter HPS lamps are available with a CRI of 65, but as color improves, efficacy and life are significantly reduced. Not a point source if narrow beam distribution is required
Disadvantages:
Not interchangeable with other lamps and ballasts. No competition. Only one manufacturer per lamp style (donut, reflector, globe) Limited to diffuse distribution Limited wattages and lumen output for each style Requires magnetic core, which has shorter life than the lamp
Appropriate Uses:
Locations where maintenance is expensive or difficult Replacement reflector lamp for incandescent floodlight in high ceilings Locations where high lumen output and diffuse distribution is desirable (indirect kiosks in high ceilings) More information is available from the manufacturers and the Advanced Lighting Guidelines.
9.142
Disadvantages:
Low efficacy Halogen is the best at 13 to 21 lumens per watt. Shorter lamp life than alternatives Halogen is the best at 3,000 to 6,000 hours Lamp can get very hot Low voltage transformers may be required for halogen lights Point source is glary if not shielded.
Appropriate Uses:
Historic settings when CFL lamps cannot be used Applications in which color rendering is extremely important (art work, limited retail) Displays where the narrowest beam control is necessary
Disadvantages:
Rapid lumen depreciation: White LEDs may last 12,000 hours or longer, but useful life is only 6,000 hours, the point at which point light output has reduced 50%. Monochromatic color Heat buildup Cost White LEDs are still bluish and provide low lumens per watt, similar to incandescent. Both conditions are expected to improve rapidly over the next 15 years.
Appropriate Uses:
Currently used primarily in exit signage, traffic signaling, and certain special effects Excellent for projecting words or an image as in walk/dont walk signs or exit signs. FEMP recommends them for these uses. LED sources may have the greatest potential for technical improvements and new applications in the next 15 years.
9.143
Passive infrared sensors (PIR) respond to the infrared heat energy of occupants, detecting motion at the human wavelength. They operate on a line-of-sight basis and do not detect occupants behind partitions or around corners. They also are less likely to detect motion as the distance increases. Therefore, they are useful when a room is small or it is desirable to control only a portion of a space. PIR are more susceptible to false-off readings than false-ons, so tend to be more annoying to occupants than ultrasonic sensors. Dual-technology sensors combine two technologies to prevent both false-offs and false-ons. The
most common one uses both ultrasonic and passive infrared sensing to detect occupancy. The
sensor usually requires that both US and PIR sense occupancy before turning on. The lights
will remain on as long as either technology detects someone. High quality occupancy sensors
use the dual technology, since it is more reliable than each of the separate technologies used
independently. Dual-technology sensors cost more than sensors using either US or PIR alone.
Other occupancy sensor features to consider include: Mounting location Ceiling, high-wall or corner, or wall box. oom size and layout are the
R major determinants. Ceiling-mounted sensors are the most versatile because their view is less
obstructed. Wall box sensors take the place of the rooms wall switch, and they are economical
and easy to retrofit. Wall box sensors are appropriate for small, unobstructed spaces.
On-Off settings Occupancy sensors can automatically turn on (auto-on) and then automatically turn off (auto-off). Or, they can require the user to turn them on (manual-on) and then automatically turn off. Manual-on sensors save more energy because the lights do not turn on when the user does not need them. Auto-on sensors are useful in applications where the users are not familiar with the layout and switch locations, or where finding a switch would be inconvenient. Sensitivity Most sensors can be adjusted for the desired degree of activity that will trigger a sensor response. The time-delay (i.e., the time elapsed between the moment a sensor stops sensing an occupant and the time it turns off) can also be selected. The setting can range from 30 seconds to 30 minutes, and the choice becomes a balance between energy conservation, user tolerance, and lamp life. We suggest no less than 15 minutes if controlling instant start ballasts. Multiple level control Occupancy sensors are effective for multiple level switching in spaces where full off is not acceptable, but occupancy is not continuous. By using a two- or three-level ballast, or multi-lamp fixtures with lamps wired separately, the lowest level may be allowed to operate at most hours, but when occupancy is sensed, the light level increases. This is a useful energy saving strategy in areas where safety or security requires some light at all times, such as certain enclosed stairs, security corridors, restrooms, etc. Of the two strategies, multi-level ballasts have the advantage of keeping the lamp warm, reducing early burn-outs caused by frequent switching. Daylight Controls. Daylight controls are photoelectric devices that turn off or dim the lights in response to the natural illumination available. Depending on the availability of daylight, the hours of operation and the space function, photoelectrically-controlled lighting can save 10% to 60% of a buildings lighting energy. This can translate into even more savings since daylight availability coincides with the hours of the day when peak demand charges apply. Smooth and continuous dimming is the preferred strategy for automated daylighting controls in offices or other work areas, since it is not distracting to the workers. The photosensor adjusts the light level based on the amount of natural light sensed by sending a signal to the dimming ballast. The less
9.144 O&M Best Practices Guide, Release 3.0
expensive dimming ballasts with minimum settings of 20% of full output are appropriate for daylight dimming (EPRI 1997). The two strategies, closed-loop and open loop, are based on photosensor locations, and the correct sensor location is essential. In a closed loop system, the sensor is located above a horizontal surface to detect the light reflecting off that surface from both electric and daylight sources. Since the sensor is reading reflected light, the reflective characteristics of the surface should remain constant. Consequently, sensors are located over a circulation area, rather than a workstation where the reflectivity of the Figure 9.12.3. Photosensor and workers clothes or desktop contents might change. In an openfluorescent dimming ballast for conloop system, the sensor is located near the window in such a way tinuous daylight dimming. to only detect daylight. In both systems, the sensor must not pick up the direct illumination from the electric lights. Sensors can control more than one dimming ballast but the luminaires being controlled must all have a similar orientation to the natural light. For example, trees in front of several windows define a separate lighting zone. Time-delay settings are used to slow down the response to rapid changes in natural lighting conditions, providing more steady lighting. Switching the lights off when sufficient natural lighting is present is a less expensive strategy, but not as acceptable to the occupants. This approach is most commonly found in outdoor applications controlling parking lot lighting for example. In buildings, a stepped approach to daylight switching is sometimes employed, in which only some lamps are switched off in multi-lamp luminaires. Alternately, daylight switching is used in rooms where continuous occupancy is not common, such as corridors, cafeterias, atria, or copy rooms. Pre-set Controls. Switching, dimming, or a combination of the two functions can be automatically preprogrammed so that the user can select an appropriate lighting environment (scene) at the touch of a button. Each scene uses a different combination of the luminaires in the room (sometimes dimmed) to provide the most appropriate light for one of several planned activities in that room. A pre-set controller and wiring plan organizes this. For example, the occupant of a conference room could select one pre-set scene from a five-button scene selector wall-mounted in the room, labeled Conference, Presentation, Slide Viewing, Cleaning, and Off. This allows multiple lighting systems to be installed to meet the varying needs of separate activities, but prevents them from all being used at full intensity for every activity. A pre-set scene should be included for the cleaning crew, which should use the most energy-efficient lights that will allow them to do their work. Time Controls. Time clocks are devices that can be programmed to turn lights on or off at designated times. These are a useful alternative to photoelectric sensors in applications with very predictable usage, such as in parking lots. Simple timers are another option, turning the lights on for a specified period of time, although there are limited applications where this is appropriate, e.g., library stacks. A time-controlled sweep strategy is sometimes effective. After normal hours of occupancy, most of the lighting is turned off (swept off), but if any occupants remain, they can override the command in just their space. Override controls can be wall switches located within the space or be activated by telephone or computer. These systems typically flash the lights prior to turnoff, to give any remaining occupants ample time to take action. There is usually more than one sweep operation scheduled after hours until all lights are turned off.
9.145
Centralized Control Management. Automated Building Management Systems (BMS) are becoming more common in medium- and large-sized facilities to control HVAC, electrical, water, and fire systems. Incorporating lighting controls is a natural step in efficient management, and centralized lighting control systems are available that can interface with building maintenance systems while providing data on lighting operation. However, in some cases, centralized systems are not appropriate for some functions, such as managing the dimming controls. The technological advance that may change this is DALI (digital addressable lighting interface), a communication protocol that allows an entire lighting system to be managed with computer software. This is promising for situations that require sophisticated control and flexibility for lighting reconfiguration. The DALI system is being designed based on an international standard so that various system components are compatible.
Although maintenance personnel may handle routine maintenance such as changing lamps or cleaning luminaires, all trouble-shooting and repair must be handled by licensed electricians. All personnel must be properly trained and equipped. All maintenance personnel shall be provided with and instructed in the use of proper tools and
equipment such as protective hand tools, fall protection such as safety belts or harnesses, hard
hats, goggles, gloves, and testing tools.
All maintenance of lighting equipment must follow the lockout/tagout standard in OSHA 1910.147 - The Control of Hazardous Energy. This standard applies to the control of energy during servicing and/or maintenance of machines and equipment. Employers must utilize procedures for affixing appropriate lockout devices or tagout devices to energy isolating devices, and to otherwise disable machines or equipment to prevent unexpected energization, start-up or release of stored energy. The employer must be able to demonstrate that the tag-out device provides an equivalent level of safety to the lock-out device in that particular situation. Consult the OSHA website for the U.S. Department of Labor at www.osha.gov. Special precautions should be taken near high voltages and lighting components such as HID
capacitors that may retain their electric change after the system has been de-energized. See
OHSA.
All forms of lifts, scaffolds, and ladders must meet OSHA standards for construction and use. Portable scaffolds, telescoping scaffolds, and personnel lifts are typically safer than ladders, by providing a firmer footing and space for tools, replacement items, and cleaning materials. Ladders used for lighting maintenance should not be made from materials that conduct electricity, such as aluminum. Stilts are sometimes used for maintenance of low ceilings or low-mounted luminaires.
9.146 O&M Best Practices Guide, Release 3.0
9.147
9.148
Lamp Lumen Depreciation (LLD). Lamp lumen depreciation presents the decrease in light output of a lamp over time. Lamp catalogues provide both initial lumens and mean lumens, the former measured after 100 hours, and the latter occurring at 40% of the rated lamp life. New, high performance T8 lamps retain more of their lumen output than other sources (about 92%), while HPS retains only about 70% and metal halide about 65%. Mercury Vapor and LEDs have the greatest fall off in light output, so although they have longer rated lives, it makes more sense to consider replacing them before the end of their useful life. Luminaire Dirt Depreciation (LDD). Dirt and dust that settles on lamps and luminaire not only reduce the output but can also change the distribution of a luminaire (Levin 2002). The LDD factor used in lighting calculations depends on - The type of luminaire (open but unventilated, and all others) - The cleanliness of the environment - The anticipated cleaning schedule - See the IESNA RP-36-03 cleaning curves and equations to determine the best cleaning schedule. In a clean environment, some enclosed and ventilated luminaires can be cleaned every 24 to 30months, resulting in less than 10% light loss (i.e., a LDD of 0.9). An open luminaire without ventilation would have to be cleaned every 12 months to keep the light loss at the same level. In a dirty environment, luminaires require cleaning every 6 months to a year to keep light losses above 20% (i.e., a LDD of 0.8). Room Surface Dirt Depreciation (RSDD). The reflective characteristics of the interior finishes can have a large impact on the efficiency of the lighting system and the quality and comfort of the light provided. Light levels can be better maintained by regular cleaning of the work surfaces. In existing facilities, light output, comfort, and lighting quality can be improved by repainting the walls a lighter color. Non-recoverable light loss factors include: Ballast losses (the difference between rated lamp wattage and the actual input wattage) Supply voltage variations Ambient temperature of luminaire and surrounds Luminaire surface deterioration Permanent deterioration of luminaire surfaces can be minimized by the wise specification of finishes for luminaire interiors and reflectors.
Figure 9.12.5. Fluorescent lamp mortality curve
9.149
9.150
Adjusted spacing criterion and mounting height to accommodate partitions. Figure 9.12.6. Lighting uniformity and fixture spacing criteria.
9.151
When considering a retrofit or redesign, it is important to keep in mind the importance of the quality of the lighting in a space. Lighting quality is just as important, and oftentimes more so than quantity of illumination. The IESNA Handbook, Ninth Edition, Chapter 10, contains lighting design guides for a wide range of space functions. These outline the most important qualitative needs, as well as the recommended light levels for each function. Uniformity There should not be a wide range of differences between the highest and lowest
brightness in the space. The existence of partial height furniture partitions may significantly
reduce uniformity, requiring a closer spacing or wider distribution of luminaires. Avoid harsh
shadows or patterns (see Figure 9.12.6).
Spacing Criterion Manufacturers provide the maximum spacing between luminaires that
will maintain acceptable uniformity. However, this spacing criterion assumes that a room is
unobstructed. If a room has partial height furniture partitions, tall files, or other obstructions,
the spacing criterion should be reduced by a factor of 0.75 to 0.85.
Lighting Walls and Ceilings The perception of occupants that the lighting is too bright, comfortable, or too dim is based more on the brightness of the room surfaces and vertical partitions than that of the task or desktop. A lighting system should be designed to distribute light to the walls and ceilings as well as the task. A light colored room can increase light levels as much as 20% over a dark colored room. Cleaning the wall surfaces improves efficiency, especially in a dirty environment, but repainting a wall with a lighter color will show much greater improvement. Glare Excessive contrasts in light cause glare. It most often occurs when a bright light
source (including windows) interfere with the viewing of less bright objects. Existing
conditions of glare can be mitigated, or glare prevented in retrofits, by some of the following
recommendations:
- Shield the lamp from view with baffles, louvers, lenses, or diffusing overlays. Use only semispecular or white painted louvers and reflectors. - Increase the reflectances of room surfaces by using lighter colored paints and fabrics in a matte or eggshell finish. - Use low output (high-efficiency) lamps in the field of view. T5HO lamps are very bright and best used in indirect applications. - Decrease the contrast between fixtures and ceilings by adding uplight or selecting luminaires with an uplight component. Color For almost any task, color discrimination aids visibility. Light sources are typically described by their correlated color temperature (CCT) and their color rendering index (CRI). For most workplaces, use fluorescent lamps in the 80 to 85 CRI range, and metal halide lamps at 80 and higher. For most workspaces, CCT between 3500 and 4100 are acceptable. For reference, 3000 Kelvin CCT is warm, 3500K is neutral, and 4100 K and higher become increasingly cool in appearance. Sunlight is in the 4000 to 6000K range, and daylight is in the 5000 to 10,000 K range.
9.152
A commissioning plan contains the following elements: design intent, design features, calibration levels, methods of verification, documentation requirements, schedules, and checklists. Establish schedules for relamping, cleaning, recalibration, and reevaluation of the lighting system. Intervals for recommissioning should be based on the type of equipment. See lighting
controlsbelow.
9.153
Specify that the ballasts and lighting controls be factory pre-set to the greatest extent possible.
This shall not remove the responsibility from the contractor for field calibration if it is needed.
Specify calibration levels to the extent they can be known prior to installation.
Aiming Some lighting equipment is sensitive to orientation, such as spotlight, wall washers, and occupancy sensors. A pre-aiming diagram can be specified or requested prior to installation, so that the contractor can make reasonable adjustments to the equipment during the initial installation. Calibration If calibration settings were not specified initially, the facility manager should
contact the manufacturer of control equipment directly for assistance.
Ensure that the commissioning is complete PRIOR to building occupancy. Even a few days of an improperly calibrated control device can turn occupants against the system, resulting in huge energy waste.
9.12.5.3 Cleaning
The intent of cleaning lamps, luminaries, and room surfaces is to return them to their original condition recovering any interim losses in light output. It is important to use the proper cleaning compounds and strategies, so that luminaire surfaces are not damaged. Different surfaces require different cleaning compounds. In lieu of manufacturers instructions, the following represents some guidance.
9.154
Never clean lamps that are operational or still hot. Use very mild soaps and cleaners, followed by a clean rinse on most surfaces. Silver films require the mildest 0.5 % solution and a soft damp cloth. Avoid strong alkaline cleaners or abrasives cleaners. Glass cleaners may be used on porcelain or glass but the latter requires an additional clear rinse. To avoid static charge on plastics, use anti-static cleaning compounds. Do not dry-wipe plastic after a rinse, as this will create an electrostatic charge. Drip-drying creates streaks. Vacuuming is the best method for drying plastics.
9.155
Calibration(a)
Time delay: 15 minutes Sensitivity: Medium high Manual-on Auto-off Time delay: 15 minutes Sensitivity: Medium High illuminance before dimming begins Time delay: 5 minutes Fade rate: 1 minute Sensitivity: See manufacturer Time delay: 10 minutes Dead band: 15 footcandles Sensitivity: See manufacturer High end trim at 95% (incandescent only) Time delay Fade rate Time delay Fade rate On and off times, differ for weekends, holidays. Multiple settings depend on space function and occupancy. Daylight savings
Notes
1,2 1,3
Daylight dimming
Daylight switching
Manual dimming Automatic dimming Pre-set dimming Automatic timers Astronomical time clocks
6 7 7 8
a) Start with these settings and adjust upward and downward as required. (1) Time delays shorter than 15 minutes are likely to shorten lamp life unless programmed ballasts are installed. (2) Wire ceiling sensors to an automatic or Sentry-type switch for manual on operation. (3) Ensure that occupancy sensors can be set to manual on without over-riding the automatic off functionality. (4) Set the illuminance level 20% to 30% higher than the designed light level for the electric lighting. Thus, if 30footcandles of electric light is provided, lamps should not start to dim until the daylight and electric light together provide 36 to 39 footcandles on the desktop. (5)Photosensor controlled switching or multi-level switching (sometimes called stepped dimming) is seldom acceptable to occupants in full time work environments. Set a wide dead-band of at least 15 footcandles to prevent cycling. (6) Slightly reducing the maximum light output of an incandescent lamp extends lamp life. It is not recommended for halogen lamps and is not effective with fluorescent sources. (7) Settings will depend on specific application. Time delays and fade rates are not recommended for pre-sets that are controlled by the occupants (rather than part of an automated program or AV sequence) because if the occupants do not see an immediate response, they often repeatedly turn lights on and off or try other pre-sets. (8) More energy is saved by tailoring the timeclocks more closely to the specific spaces being controlled and by providing more discrete schedules, i.e., one for Saturday and one for Sunday, rather than the same for the weekend.
Troubleshooting Occupancy sensors turn lights on when they are not needed. Is the sensor responding to movement in the corridor outside the office, currents from the air diffusers, or it is causing the lights to burn even when daylight is sufficient or preferred. Ultrasonic sensors are more prone to false on, but less prone to false offs, because they are more sensitive to subtle movement like occupants typing or writing. Start with adjusting (reducing) the sensitivity setting slightly, reducing the sensors sensitivity to motion, without creating a problem with false offs. If the occupants are agreeable, setting the sensor to manual on operation (if it is connected to, or integral with, a local switch) is the most energy efficient and increases lamp life. Mask the sensor so that it does not see motion outside the room.
9.156 O&M Best Practices Guide, Release 3.0
Occupancy sensors turn lights off when occupants are still in the space. Check to confirm that sensor is not in test mode. Increase the sensitivity setting. Increase the time delay, but not longer than 30 minutes. Consider replacing infrared sensor with more sensitive ultrasonic sensors.
Evaluate the number and distribution of the existing sensors and verify if the coverage is
sufficient. (Partial height partitions and other vertical obstructions must be taken into
consideration.)
Daylighting controls dim the lights too much. Verify light levels. If they meet design criteria, the problem may be one of window glare or
excessive contrast. Verify that blinds are adequate to control glare. Diffuse shades may be too
bright when sun hits them.
Maximize the fade rate. Dimming should be smooth and continuous and not perceptible to the occupants. Verify with manufacturer that product has a continuous dimming response, not a threshold dimming response. The latter is appropriate for spaces like warehouses, but not for offices or spaces with stationary workers. Increase time delay to 10 minutes so that lights do not respond to sudden changes like cloud
movements near the sun, or people walking under the photosensor.
Verify that the photocell is properly located over a space that does not change from day to day, like the carpet of aisles between cubicles or an unadorned wall. A photocell over a desktop will respond to the objects on a desk or the occupants clothing, and may dim lights more on days that the occupant wears a white shirt. Re-calibrate the photosensor at night and again during hours of daylight. Follow manufacturers procedure. Fluorescent lamps flicker when dimming ballasts are at the lowest end of the dimming range. Consult the ballast manufacturer and verify wiring is correct. Replace the ballasts. If the problem is extensive or attributable to the signal sent by the photosensor, increase the
lowest setting, but not higher than 30%.
9.157
Generally, the diagnostics of lighting systems involves the evaluation of the basic characteristics of lighting: Quality and quantity of light. Equipment types and efficiency, condition, and cleanliness. Control condition/settings. Energy usage. For some of these characteristics, visual inspection and physical testing is appropriate and requires no special tools. For others some basic tools can be helpful. Illuminance (light) meter Illuminance meters are often referred to as a light meters which is a generic term that also includes the meters used by photographers (which is not what is needed for building lighting). Illuminance meters come in many styles at a range of costs. Most will do an adequate job of evaluating basic light levels in building spaces. Light levels should be taken at the spaces where the specific tasks are to be performed such as desktops for office work, hallway floors for egress, etc. Light levels will change over time as lamps age. However, with modern equipment this is a relatively slight effect and is not typically considered a metric used to make changes to equipment or replace lamps. The most important measurement of light levels is an evaluation when systems are initially installed, equipment changes are made, or an O&M program is initiated. Light levels that are higher than necessary to provide appropriate lighting or higher than designed are an opportunity for energy savings as light level and kWh usage are directly related. The required light levels (illuminance) for building areas will depend on the expected tasks. The widely accepted and referenced quality and illuminance recommendations are developed by the Illuminating Engineering Society of North America (IESNA), and can be found in Chapter 10 of the IESNA Handbook, Ninth Edition. The building tenants or other regulatory organizations may also have specific requirements for the activities to be performed in the building. Energy/lighting/occupancy loggers Measurements of individual lighting fixtures or panels can provide specific lighting power information that if tracked over time can help identify controls savings opportunities. However, the equipment to support these continuous measurements can be expensive to install and maintain. Less costly options that provide similar useful results are individual lighting loggers than can measure lighting on/off schedules for long periods of time with the capability to download the data to any computer for analysis. This kind of data can identify areas where lighting is left on after hours. Similar occupancy based loggers can specifically identify lighting that remains on when spaces are unoccupied. This information can be used to identify overlit spaces as well as good applications for occupancy sensor controls. These loggers are available from a variety of sources. These can be found on the world-wide web or in the report, Portable Data Loggers Diagnostic Tools for Energy-Efficient Building Operations (PECI 1999). Flicker checker For hard-to-reach areas (high ceilings), it is often difficult to determine the type of lighting installed (electronic, magnetic ballast). There is a simple tool available to help determine the characteristics of ballast type (and therefore often lamp type) installed. A common version of this tool is a flicker checker used to determine electronic versus electromagnetic ballasts
9.158
available from Sylvania (1-800-544-4828). It operates like a simple toy top and will indicate whether the operating ballast above is a 60 Hz type or electronic high frequency type. Typically the 60 Hz type will be operating T12 technology lamps. The high frequency may be operating T12 or T8 technology. Solar data When considering the application of daylighting into building spaces, it is important to understand the potential of the building space and the capability of the sun in your area to provide adequate daylight. This involves evaluating the tasks in the space, characterizing the configuration of the space including size and shape of windows or skylights, and assessment of the solar availability in your location. Solar availability data is maintained by the National Oceanographic and Atmospheric Association (NOAA) at www.noaa.gov. Available data includes number of hours of sunshine, number of clear, overcast, and partially cloudy days in a number of cities across the United States based on weather charts. Exterior illumination of sun and daylight can be found for any U.S. latitude through the IESNA daylight availability publication or the ASHRAE handbook. Sun angles can be determined by the Pilkington LOF Sun Angle Calculator, available from www.sbse.org/resources/sac/.
9.12.5.7 Economics
Operations and maintenance activities and equipment represent real costs to a facility and must be evaluated like any other proposed action. Some potential actions can be evaluated using simple methods to provide appropriate costeffectiveness analysis such as the replacement of incandescent exit signs with reduced-wattage LED signs. The cost of energy saved is easy to calculate based on the wattage difference, 24-hour operation, and local utility rates. The cost of the new exit sign divided by the cost savings provides a simple measure of the time required to pay off the new sign with energy savings (payback period). This is often all that is needed to determine whether the replacement is a good idea. In other cases, more complicated analysis is required. Large cost items such as more advanced control systems may require longer term investment spanning many years. These types of investment decisions will often require more comprehensive cost analysis that involves more parameters to determine their cost-effectiveness. These often include: Installation costs Equipment life Replacement equipment cost Replacement labor Interest rate Fuel cost Fuel escalation rates. With more advanced resulting analysis metrics such as: Return on investment Life-cycle cost.
9.159
Software tools are available from many sources to perform this type of analysis. The Federally supported Building Life Cycle Cost (BLCC5) tool for advanced economic analysis is one such tool that is available from the USDOE at www.eere.energy.gov/femp/information/download_blcc.cfm.
Visual inspection
Inspect fixtures and controls to Semi-annually identify excessive dirt, degraded lenses, inoperable or ineffective controls. Lamps and fixture reflective surfaces should be cleaned periodically for maximum efficient delivery of light to the space Clean surfaces allow maximum distribution of light within the space Replace yellowed, stained, or broken lenses or louvers Lighter colored surfaces will increase light distribution efficiency within the space For larger facilities consider group relamping Rapid change in technology may result in significant savings through relamping or simple retrofit. Measure light levels compared to tasks needs in typical spaces. Identify areas for reduction or increase in illuminance Identify areas where daylighting controls could be used Identify areas where local automatic controls could be used 6 to 30 months, depending on space and luminaire type
Clean walls and ceilings Replace degraded lenses or louvers Repaint walls and replace ceilings
Replace burned out lamps Evaluate lamps and ballasts for potential upgrade Survey lighting use/illumination levels
As needed or on group schedule Every five years or on group relamping schedule Initially and at task/tenant change
9.160
9.12.7 References
10 CFR 434. U.S. Department of Energy. Energy Code for New Federal Commercial and MultiFamily High Rise Residential Buildings. U.S. Code of Federal Regulations. 40 CFR 273. U.S. Environmental Protection Agency. Standards for Universal Waste Management. U.S. Code of Federal Regulations. Advanced Lighting Guidelines, New Buildings Institute, 2003, available from www.nbi.org. ANSI/ASHRAE/IESNA. 2001. Energy Standard for Buildings Except Low-Rise Residential Buildings, ASHRAE/IESNA Standard 90.1-2001 American Society of Heating, Refrigeration and AirConditioning Engineers (ASHRAE). Daylight Design Smart and Simple, Electric Power Research Institute (EPRI) TR-109720, 1997, available from www.iesna.org. DDC Lighting Handbook. 2004. New York City Department of Design and Construction. IESNA Guidelines for Upgrading Lighting Systems in Commercial and Institutional Spaces (LEM-3-07), available at www.iesna.org. Levin, R.E., W.E. Bracket, N. Frank, J. Burke. 2002. Field study of luminaire dirt depreciation. Journal of the IES 31(2):26. Lighting Controls Patterns for Design, Electric Power Research Institute (EPRI) TR-107230, 1996, available from www.iesna.org. PECI. 1999. Portable Data Loggers Diagnostic Tools for Energy-Efficient Building Operations. Prepared for the U.S. Environmental Protection Agency and U.S. Department of Energy by Portland Energy Conservation, Incorporated, Portland, Oregon. Recommended Practice for Planned Indoor Lighting Maintenance (IESNA/NALMCO RP-36-03). Joint publication of the Illuminating Engineering Society of North America (IESNA) and the interNational Association of Lighting Management Companies (NALMCO), available from www.iesna.org. Toxic Substances Control Act. 15 USC Z601 et. seq. (1976). UNEP, 2006. Energy Efficiency Guide for Industry, 2006. United Nations Environmental Program. Washington, D.C.
9.161