R134at+ - THE PREMIUM 134a REFRIGERANT Why R134a+? With the phasing out of ozone depleting refrigerants under the Montreal Protocol, R12 ceased production, As a replacement, manufacturers worldwide adopted R134a as the refrigerant of choice, New systems were developed using R134a as the reference refrigerant and existing R12 systems were, and are still being, retrofitted to R1B4a. R134at is a further development to optimise or enhance the performance of both retrofitted and genuine R134a systems. ‘The Benefits of R134a+ Prossure/Temperature (P/T) Relationship Compatibility. RI34a based refrigerant have a pressure temperature relationship very close to R12 — especially in the evaporating range where the pressure of the refrigerant determines the evaporator temperature and therefore the cooling capacity of the system. ‘The advantage of P/T compatibility is that the system pressure and flow control devices (The Compressor and the TX Valve or Expansion Tube) do not need ‘modification in a retrofit situation in a majority of cases, Evaporator Pressure/Temperature Relationships (At Normal Low Side Pressures) 10) 99. 44 418 47 8 415 17 134 19 6 133 19 151 22 4 154 22 169 24 2 474 25 187 27 0 191 28 207 30, 2 213 31 228 33 4 236 34 250 36 6 260 38 273 40(Figures rounded off for practical purposes. Technicians cannot read automotive gauges to decimal point accuracy.) ‘The area where R134a has a minor (marginal) limitation is in the condensing range. In an automotive air conditioning system the condenser is a critical component in that it must be capable of dissipating al! heat absorbed in the evaporator. If its performancelefficiency is reduced the ability of the refrigerant to be “cleaned” of heat in the condenser is correspondingly reduced directly affecting the ability of the evaporator. Itean no longer absorb its full capacity. Professional air conditioning technicians would have observed this through recognising moder R134a designed systems are fitted with high cfficiency parallel flow or dual pass serpentine condensers. ‘These are specifically designed for maximum heat dissipation for ‘optimum system performance. in the development of R134a+ has been to develop a refrigerant that optimises system performance. Dependent on the design and dynamics of the condenser, testing across a range of styles, designs and sizes of condensers has shown a significant reduction in head pressures (high side pressure) is achievable with RISdat, together with reduced “on times” (faster cycling rates), and faster pull down, NORMAL PRESSURE CURVE - CORRECTLY OPERATING SYSTEM aS CHARGE RATE, Optimisation Zone for 134a+ - Pressure Reductions of 120 kPa on High Side in systems gaining maximum benefit from using RI34a+, Additional Benefits of High Side Pressure Reduction Using R134a+In systems where R134a+ gives significant pressure reductions there are additional ‘operational benefits, in addition to increased system efficiencies. * Reduced Noise, Vibration and Harshness (NVH) levels that are, in many cases felt or heard in the passenger compartment, Reduced Torque engagement spikes as the clutch cycles “on’ Reduced load on the cooling system — with high condensing temperatures the cooling system is “loaded” with heat from the condenser. Testing with R134a+ shows up to 7°C reduction in condensing temperatures (at high heat loads) giving significantly reduced loads to the cooling system. Discharge Line Temperature Reduction “The modern motor vehicle can generate very high discharge line temperatures. The high under bonnet temperatures, restricted airflows around compressors and the high superheat generated in a modern highly efficient compressor all contribute to discharge line temperatures in excess of 120°C in some compressors. ‘Supetheat ~ the heating of the vapours in the suction line and the compressor can lead to reduced life or failure of the compressor. It is the high discharge temperatures plus the high pressure that loads the pump to unacceptable levels. This is the reason why ‘many manufacturers incorporate a superheat switch into the compressor. RI34at can offer significant benefits here. With a lower condenser pressure and the corresponding lowering of condensing temperature (up to 7°C) the discharge line temperatures were also reduced by 7°C. Our testing showed 97°C reduced to 90.2°C {at 35°C ambient, 40% relative humidity) as an example of what can be achieved in an optimised R134a+ system. Important Note: R134a+ does not lower the superheat level in all tests conducted. That is determined by the operating system and the heat loads on the suction run and compressor. WE DO NOT CLAIM SUPERHEAT REDUCTION - IT IS DISCHARGE LINE TEMPERATURE REDUCTION. Examples From Test Data: Nissan Patrol 1997 33°C 50% RHHigh Side Pressure (Stabilised) S minute test 1500r/min) Condensing Temperature (Refrigerant) (Measured External Tube Temperature) Discharge Line Temperature (measured) Superheat 86°C - 62°C = dat Te High Side Pressure (Stabilised) Condensing Temperature (Refrigerant) (Measured External Tube Temperature) Discharge Line Temperature Superheat 80°C - STC = 1820 kPa 66°C 62°C 86°C 24°C 1610 kPa 61°C src 80°C 23°CEvaporator Efficiencies Evaporators are the components responsible for the absorption of cabin heat. Evaporator efficiencies are principally determined by: ‘+ The temperature of the refrigerant flowing though the evaporator, The colder itis to absorb heat. * The filling of the evaporator— the volume of refrigerant in the evaporator determines the amount of heat that can be removed from the air. A good analogy ‘a sponge — evaporators (or more correctly the refrigerant in the evaporator) act 8a sponge to “suck up” heat from the cabin, The bigger the sponge the more heat can be absorbed. + The characteristics of the refrigerant — can it absorb heat at an optimum rate? This is determined by: ‘© The base characteristics of the reftigerant. (Its enthalpy characteristics or its latent heat of vaporisation value) centers the evaporator. (In liquid state ~-slightly determined by the efficiency of the condenser (previously discussed). R134a can optimise system efficiencies by maximising condensing capability and by ‘having a high capacity to absorb heut in the evaporator. Test Results Evaporator Efficiencies ‘Our testing showed parallel findings to condensing pressures/temperatures. Tn systems that gain maximum benefit from using R134a+ The initial pull down time (to get the system down to its eycling point) reduced — RIG4at has the ability to cool a cabin faster. * The cycling rate “on time” decreased in some systems (optimised systems) Using R134a+ there was a reduction from: 20 seconds on — 30 seconds off (R134a) to 17 seconds on — 30 seconds off (R134a+)Important Note: ‘The evaporator temperature did not change -— this is controlled by the thermostat — vent temperature reductions are only valid data when cycling points (thermostat settings) cannot be reached. (Sce next point.) ‘Under high heat load test conditions marginal reductions in vent temperatures were achieved 10.4°C down to 9.8°C at 34°C — 50% RH. (Medium fan speed. System stabilised.) Evaporator Efficiency Summary Potential of RI34a+ Faster pull down of cabin Faster cycling rate Slightly reduced vent temperatures under high heat loads (thermostat setting cannot be reached — evaporator can not pull down to 0°C). System Reliability Factors Correctly serviced and well maintained air condit ning systems can provide years of trouble free operation. Poor maintenance or service procedures can result in premature failure of the heat exchangers (evaporators, condensers). Heat and vibration can cause ie of any of the air conditioning components, however the biggest area of concern (and often the biggest cost to the consumer) is the compressor. Compressor failures are usually a result of the operating dynamics of the system. ‘These dynamics may include: Excessive high side (head) pressure Excessive discharge superheat Poor oil return to compressor Liquid entering the suction of the compressor (this may be either liquid reftigerant or oil) Contaminated refrigerant or oil Lack of oil in system Excessive compressor speed.How does R134a+ Effect These Operating Dynamics? Excessive Head Pressures —R134at- can optimise condensing efficiency to reduce head pressures (refer optimisation graph) in normal operation, and to prevent gauge creep (the high side gauge slowly creeping) in marginally condensed systems. R134a+ will not provide protection against: Inadequate condensing/condenser airflows Severely oil flooded condensers System overcharging Discharge Superheat — discharge line temperatures can be reduced (by up to 7°C) as a result of lowered condensing temperatures (lower condensing pressure). Factors 1 and 2 combined can significantly reduce the risk of compressor failure, IIs the combination of high pressure AND high superheat that is most dangerous to compressors. Note: ‘An additional benefit of reduced discharge line superheat is that systems fitted with a superheat switch (located on the outlet of the compressor) — for protection against superheat damage can cut the clutch in normal operation at high ambient temperatures/high humidities, By reducing condensing temperatures and corresponding discharge line temperatures the system can be “held in” (operate) under higher heat load conditions, Oil Return To The Compressor — R134a+ is compatible with normal R134a synthetic oils (PAGs and Polyol — Esters). Oil return rates are not affected. RI34a+ is basically R134a with a performance enhancer. Liquid Entering Suction Of The Compressor —a system fault is required to generate this condition. R134a+ does not offer protection against this condition. It is a system design or component malfunction problem (ic. TX valve jammed open). Contaminated oii, reftigerant, lack of oil or excessive compressor speeds are all conditions over which R134a+ has no effecU/control. Summary — System Operating Dynamics — How Can R134a+ help?By reducing condensing pressures/temperatures and corresponding reductions in discharge line temperature. Variable Displacement Compressors & Evaporator Pressure Regulated Systems. ‘Newer generation systems operating on a variable displacement/constant evaporator pressure basically operate perfectly on R134at. ‘The pressure temperature relationship is the same as R134a and thereby evaporator temperature control is identical. Evaporator Pressure Regulated (EPR) and Section Throttling Valve (STV) Systems have identical low side temperature control as for R134a systems. Condensing benefits are as previously explained on both variable compressor and EPR/STV systems, condensing pressures and temperatures in systems optimising R134a¢, Corresponding gains in reduced discharge line possible, With systems optimising performance on R134: and showing condensing gains, corresponding cabin pull down and cycling rates will result (as per previously explained). Servicing Requirements RI34at is serviced using the same procedures and equipment as R134a. ‘The only difference in servicing is that technicians may notice a reduction in high side pressure of up to 120kPa (I7PSI) (at 35°C. 60% RH) on systems operating on RI34a+ (refer to optimisation chart previous). R134at is totally compatible with all R134a synthetic oils and dyes. Electronic leak detection is as for RI34a,Note: Safety glasses must be worn when working with any refrigerant, Blindness may result from unexpected discharge of R134a+—as it may with all refrigerants, Gloves should be worn as required to prevent “cold burns”. Test Program/Equipment All testing conducted under strict conditions using the following calibrated equipment: ‘Thermometer Fluke 8011 5QU interfaced with Fluke 123 Scope meter. Range: -50 to +150°C Accuracy: Within 5% (full range) Secondary accuracy check conducted using OTC Pressure/Temperature Analyser Mo ISP-300-XXXX- Accuracy: 1% (full range) (includes nonlinearity, hysteresis and repeatability). Pressure Analysis OTC Pressure/Temperature Analyser Model: MSP-300-XXXX-Y-1-Z, Range: 0 —20,000 PSIG Accuracy: Within 1% (full range) (includes nonlinearity, hysteresis and repeatability). Humidity CPS 250A interfaced with CPSS204 Humidity probeAirflow (Anemometer) cPs—AMSO All comparative testing (environmental contro! chamber and field testing) conducted under strict conditions, measuring of temperature, humidity, and airflows conducted on a “fixed” time elapsed basis to ensure accurate comparative data, Pressure/Temperature analysis conducted at 5, 10 and 15 minute test intervals. Evaporator and condenser fan speeds monitored for consistency, (See attached test data) Physical Properties Molecular Weis 102 Boiling Point @latm (deg. C) 28.9 Density of Saturated Vapour @ 1 atm 5.29 Density of Saturated Liquid @ 125 degC 1.21 Critical Temperature (deg C) 101 Critical Pressure (kPa Absolute) 4065 Flammability Limit None Ozone Depleting Potential 0 Grant Hand Automotive Mechanical Air Conditioning Consultant Douglas Mawson Institute of TAFE 10342 2, CHILLER PLANT measure 2.7.2. Maintain the proper refrigerant charge. ‘The efficiency of all chillers suffers if the system has either too litle ortoo much refrigerant charge. Also, the compressor may suffer damage if the system is overcharged. Some systems have only minimal rese capacity, making it important to charge the system precisely. Such systems are more vulnerable to loss of cfficicncy from small leaks. Other systems have a large ‘amount of reservoir capacity. In these systems, a small leak may persist fora long time before being noticed. ‘Check the reftigerant charge in your cooling units often cnough to keep the charge within proper limits. ‘This Measure gives you procedures for checking and ‘maintaining the proper refrigerant charge and explains the effeets of improper refrigerant charge. Bad Effects of Incorrect Refrigerant Charge Both the COP and the capacity of # cooling unit suffer ifthe refrigerant charge is too low. When that ‘occurs, evaporator capacity is reduced because less of its surface is wetted, and the average evaporator increases. The compressor must fy the same cooling load. == mo Fig. Refrigerant fevel sight glass in alarge chiller The ‘lass is located just bolow the center ofthe evaporator shel, to the righl of the inslrumont panel, tis 60 small hat # may ‘otline Up with the quid love. Ifs0, you can't to whethor tho liquid level is above or below the glass. tn this case, observe the glass when the machine stats. RATINGS e LJ SUMMARY ‘Afundamental chiller maintenance procedure with a significant effect on efficiency. Finding the level of charge may be tricky. Some inexpensive accessories may help. SELECTION SCORECARD ‘Savings Potential Ease of Initiation In hermetic chillers, in which the motor is cooled by the refrigerant gas, low charge can overheat the motor, reducing its life. If there is too much refrigerant in the system, the excess may back up in the condenser, reducing its effective surface area and increasing the average temperature differential across the condenser. In chillers that have a flooded cylindrical evaporator and no device to regulate the refrigerant level in the evaporator, high refrigerant level reduces the evaporation surface area. In some types of systems, excess refrigerant can travel through the evaporator in the liquid state, continuing into the compressor. ‘This can destroy a positive displacement compressor immediately, and it can destroy a centrifugal compressor gradually. How to Measure Refrigerant Charge “The most difficult aspect of maintaining the proper refrigerant charge may be measuring the charge that is presently in the system. In some cases, this ean be tricky, tedious, or both, The best method of checking the refrigerant charge depends on the type of system. Use the best method or combination of methods for your system. The following are the various methods that are available. 1 Liquid Leve! Indicators and Sight Glasses Some chiller units, and some vessels in a chiller system, may have a means to indicate the refrigerant quantity directly. These work only if a predictable ‘quantity of refrigerant remains in one partof the system. ‘The most common liquid {evel indicator is a sight glass on the vessel where the refrigerant collects. Refrigerant level sight glasses arc common. accessories of packaged water chillers. ‘They are useful ENERGY EFFICIENCY MANUAL2.1 REFRIGERANT CONDITION 343 fon these machines because all the reftigerant remains within the shell of the machine and drains freely into the evaporator. Figure | shows a typical sight glass. It ‘can be used when the machine is running or turned off, although the level is more stable when the machine is not running. ‘Many refrigerant level sight glasses are perversely ‘small, making it difficult to check the level ifit is above or below the levet of the sight glass. In such cases, it helps to look at the sight glass as the chiller is being sfarted. If the refrigerant surface is above the sight glass, you can probably see bubbles as the chiller starts, or the refrigerant level drops to the level ofthe sight glass. If the refrigerant level is below the sight glass, you may beable to see splatter on the sight glass, which indicates that the charge is low. ‘Some older units have a liquid level test cock on the evaporator shell. However, these require venting some refrigerant to test the liquid level. This practice is now considered very bad form, for environmental reasons. Inchiller systems where the components are spread ‘out, refrigerant quantity indicators do not work as well, for they may not work at all. The problem is that refrigerant migrates from one part of the system to ‘another. When the chiller is running, the distribution of refrigerant in the system varies with load. When the chiller is not running, reftigerant migrates to the coldest part of the system. For example, the refrigerant might accumulate in the condenser during winter and in the evaporators during summer. If a spread-out chiller system has a receiver (refrigerant surge tank) or a shell-and-tube evaporator, it may be practical to use a level indicator in one of these vessels. In such cases, the level indicator provides useful information only when the system is running and stabilized, Even then, the level of rftigerant varies with thecooling load. The refrigerant level indicator should be readable anywhere within the acceptable charge range. When the system is turned off, refrigerant pools inthe coldest parts ofthe system, and the level indicator ives a false reading, If your chiller system does not have an easy-to-read refrigerant level indicator, consider adding one, if possible. Ifyou do, installa placard atthe sight glass or gauge that indicates the normal range of readings, and the conditions under which the readings are valid. For example, the placard might say, “Refrigerant level indicator valid only if the compressor is running, or if the receiver temperature is at least 10°F cotder than the outside air temperature.” (See Refercnce Note 12, Placards, for tips on how to create an effective placard.) ‘Any kind of reftigerant level gauge or sight glass should be strong and well protected. A broken sight glass or gauge connection would vent the entire refrigerant charge into the surrounding space. With high- pressure refrigerants, the blowout continues at full pressure as long as there is liquid inthe system, which isa dangerous situation, ™ Discharge and Suction Pressures With all types of compression cooling equipment, you can check the state of refrigerant charge by ‘measuring the discharge and suction pressures in the system, Do this while the compressor is operating and the system isin stable operation, Larger machines usually have gauges installed that icate the evaporator and condenser pressures at all times. Figure 2 shows typical example. Use portable ‘gauges if the machine docs not have gauges installed. ‘The normal discharge pressure depends on the condensing temperature. To check system charge, use a table of refrigerant pressures and temperatures. This tells you what the condensing pressure should be at the current condensing temperature. If the discharge pressure is lower than it should be at that temperature, ‘the system is low on charge. Refrigerant pressure gauges often have the ‘corresponding saturation temperatures printed right on the gauge dials, This saves you the trouble of finding a refrigerant pressure chart, Portable refrigerant gauges typically show the saturation pressures for several of the most common reftigerants. If you need to use a refrigerant table, you can find one in many reference books. Also, refrigeration supply houses common give ‘away refrigerant tables that are printed on handy cards. If the type of refrigerant used inthe chiller system has ‘been changed, be sure to use a reftigerant table forthe ‘current refrigerant, If the refrigerant charge is low, both the discharge and suetion pressures will be lower than normal. The discharge pressure is low because there is not enough gas in the system for the compressor to squeeze to the normal discharge pressure, The suction pressure drops Fig. 2 Evaporator and condonser gauges These tell you Immediately whether the machine has the minimum amount (of refrigerant fr efficient operation. They do not tll you the ‘actual amount. The condenser pressure provides an uncertain Indication of excessive charge. ©D. K.srulfmnghosy 1999. AU Rights Reserved.344 2. CHILLER PLANT because there is not enough liquid refrigerant in the ‘evaporator to boil off vaporat the normal vapor pressure. ‘As a result, the vapor expands into the compressor suction, lowering its pressure. In other words, the compressor starts to act like a vacuum pump. Low suction pressure also creates abnormally low suction temperature, This occurs because the reffigerant tgs is cooled below its saturation temperature by the greater expansion, The suction temperature can eventually fall enough to freeze the evaporator coil. In ‘a water chiller, this can cause major damage. Suction pressure could be lower than normal for cofher reasons, such as obstructed air flow through an air-cooled evaporator. For example, opening the ‘evaporator coil access panel in an air handling unit short- circuits the flow of air around the coil, causing its refrigerant pressure to drop. Discharge pressure is much less reliable asa clue excessive refrigerant charge. If the condenser floods from excess charge, its cooling capacity is reduced, so the discharge pressure rises. A noticeable pressure rise ‘occurs only under high load. A condenser that is heavily flooded with excess refrigerant will also cause cooling water or cooling air temperatures that are lower than normal, because the condenser is not rejecting as much heat. However, this symptom is subtle, (ifthe discharge pressure is lower than normal and the suction pressure is higher than normal, the compressor may be worn out, or the compressor or system may have an internal leak from the discharge side to the suetion side, or the system may have hot ges bypass.) So, the suction and discharge pressures area reliable indicator of low charge, and the discharge pressure is a less reliable indicator of excessive charge. However, system pressure cannot tell how much refrigerant isin the system within the normal range of charge. As long as there is enough liquid within the system to keep the ‘evaporator supplied, the readingsare normal. In systems ‘without refrigerant quantity indicators, you have to check the reftigerant pressure at appropriate intervals to detect the first sign of inadequate charge. When leakage finally causes liquid starvation in the evaporator, pressures start todeclinc. ‘The rate of dectine depends on the leakage rate and on the volume of refrigerant in the system. (On the other hand, air in the system causes all pressures to be higher than normal. This can mask 2 Tumenae cue. cone 1y -ostaNeeoMNSen Sion Corie open Fig.3 Evaporator liquid line sight glass. tis generally located as shown here, lose to where the refrigerant liquid enters tho evaporator. Bubbles In tho sight glass while the system Is running probably indicate low refrigerant charge, bul they may also incicalo an obstruction ofthe refigeranlinin the direction ofthe condenser. ENERGY EFFICIENCY MANUAL2.7 REFRIGERANT CONDITION 345 low refrigerant charge. Keep airout ofthe system at all times. This is covered by Measures 2.7.1 and 2.7.3. = Evaporator Liquid Line Sight Glass In chillers that use a throttling type of refrigerant metering device (an “expansion valve,” capillary tubes, etc. to control the flow of refrigerant to the evaporator, a sight glass may be installed in the refrigerant fine leading tothe evaporator. Figure 3 shows where to look for the sight glass. Bubbles in the sight glass indicate that there is not ‘enough liquid in the system to keep the line filled. Bubbles first appear under high cooling load, when liquid is being drawn out of the line most rapidly. Bubbles that occur when the system first starts may be normal, and do not indicate low charge. Bubbles in a sight glass are not a foolproof ication. If the sight glass is located upstream of a partially obstructed filter or dryer, the back pressure may ceep bubbles from forming even when the charge is low. Conversely, ifthe sight glass is downstream of a clogged filter or dryer, the reduced pressure at the sight glass ‘may cause bubbles to form even though the amount of refrigerant in the system is proper. Adding more refrigerantbased on this false indication may overcharge the system and eause compressor damage, A liquid line sight glass cannot reveal excessive refrigerant charge. Suction Gas Superheat In direct-expansion chiller systems (which send the refrigerant directly into the cooling coils), low charge is indicated by high superheat in the gas leaving the evaporator, especially when the compressor is operating at fall load. Superheat is the excess of the gas suction temperature above the gas saturation temperature, When the evaporator becomes “starved” for refrigerant, the available refrigerant boils ff quickly and the unsatisfied heat load of the evaporator superhecats the refrigerant as excessively. In systems that use a thermostatic expansion valve, the valve is designed to maintain a fixed amount of supetheat. ‘The purpose of the superhcat is to ensure that liquid refrigerant does not enter the compressor. Do not let this superheat fool you into believing thatthe charge is low. If the superheat setting of the valve is is typically LO°E to 20°F, or 5°C to 11°C), the charge is probably not low if the superheat remains essentially the same at all loads. ™ Condensate Subcooling {In systems with air-cooled condensers, excessive charge is indicated by excessive subcooling of the refrigerant. Subcooling is cooling of the liquid refrigerant below its saturation temperature. When the system is overcharged, the condenser fills with liquid refrigerant, the condenser capacity drops, and the liquid lingers in the condenser long enough to become excessively subcooted ‘The difference in temperature between normal and subcooled reftigerant from a condenser is small. This makes the test {oo subile for any but experienced technicians. Look for condenser subcooling as confirmation of excess charge if the discharge pressure is oo high. “This symptom is accompanied by abnormally high ‘condenser pressure, especially at high cooling load, = Bleeding Refrigerant Pressure ‘Asa last resort, you can bleed reftigerant from the system until the operating pressures drop, and then add the recommended amount of extra refrigerant. Do not his method with any environmentally harmful refrigerant unless you have the equipment to salvage the refrigerant, Should You Add a Receiver? ‘All chiller systems have a certain amount of storage volume for liquid refrigerant, but the amount varies widely. Ample refrigerant storage capacity ensures that refrigerant is available to the evaporator. Itcompensates for accumulation of refrigerant in different parts of the system under different operating conditions. It prevents back-flooding of refrigerant into the condenser, And, it provides a reserve to make up for leakage. ‘Some chillers inherently have large storage volume, For example, packaged centrifugal water chillers store a farge amount of refrigerant in their evaporator shells. On the other hand, direct-expansion chillers may have little storage eapecity, because air coils have small Kquid volumes, In the past, it was common practice to install a “receiver” in such Systems, which i simply a storage tank, or surge tank. Different chiller system designs may have receivers in different parts of the system. It has become commonplace to eliminate the receiver from chiller systems as a cost saving measure. In such systems, storage volume is limited to the condenser itself and to the piping downstream of the condenser. Therefore, arelalively smal overcharge may cause refrigerant to back up into the condenser, and a relatively small undercharge may starve the evaporator of refrigerant. For example, a difference ofa few ounces of refrigerant charge may affect chiller performance in a small split system, ‘In systems that lack reftigerant storage capacity, it inay be desirable to add a receiver to the system. The mechanical installation is usually not complicated, but it should be done by a refiigeration specialist familiar with proper piping practices and other aspects of assembling cooling systems. Finding the proper location for the receiver in the system requircs @ clear understanding of chiller system design. ©D. K. Wulfinghoff 1999. AN Rights Reserved.346 2. CHILLER PLANT Installing a receiver is not a substitute for keeping tho system fice of leaks. Ifthe system operates properly when itis properly charged, it probably does not need a receiver. Instead, put your emphasis on proper charging procedure and checking for leaks. How to Add Refrigerant Follow the refrigerant charging procedures specified by the manofecturer. If your system does let you measure the refrigerant charge directly, find the point ‘of minimum charge as deseribed previously. Then, add reffigerant in the amount specificd by the manufacturer. Ifyou use a large bulk container of refrigerant, put iton a portable scale as you charge the system. Calculate the amount of refrigerant added from the change in weight. Be careful to keep air from entering the system when you rechargeit. This requires great care ifthe refrigerant inthe chiller is below atmospheric pressure. Even with high-pressure refrigerants, be careful to purge all the refrigerant gauge and filling hoses before opening the chiller service ports. If you are filling a chiller system that has been ‘opened to the atmosphere, you have fo use a vacuum pump to remove all airand vapor from the system before recharging. Don’t try this without training. Chiller servicing should be done only by technicians who fully understand what they are doing, Inadequate training of ‘maintenance personnel is a common cause of chiller damage and inefficiency. ECONOMICS SAVINGS POTENTIAL: Up to 20 percent of chiller ‘operating cost. COST: Usually minimal. PAYBACK PERIOD: Short. TRAPS & TRICKS SKILLS AND TRAINING: Understand how refrigerant travels in your chiller system. Know the best methods ‘of checking the charge in that type of system. Invest in {raining the right person for this responsiblity. Keep ‘unqualified people from messing with refigerant charge. They can doa ot of harm. SCHEDULING: This is another function that tends to be forgotten. Ifthe charge n your chilers can be checked ‘easily, put a colurin for refrigerant level on the chiller ‘operating log. Otherwise, schedule checks in your maintenance calendar. (You do have a chiler operating Jog and a maintenance calendar, right?) B. ENERGY EFFICIENCY MANUALReftigerant Safety - Application Considerations Page | of 4 ¥ Book store 1 puitding Services 1 case studies engineers Newsletter » Products 1 Market Segments «Financing » Industry tssues » News Room Parts And Suppltes » systems » Training commerctat: Local Application Considerations Bolling Point Differences. An argument can be made that low pressure, high bolling point refrigerants are inherently safer than high-pressure fluids. The reasoning arises from two factors. First, most of the refrigerant will remain a liquid or condense into a liquid at temperatures below the boiling point. As a result, airborne concentrations impacting inhalation and flammability will be lower than for a high pressure, low boiling point fluid. The boiling temperatures at normal atmospheric pressure are 24°C (75°F) for R-11 and 28°C (82°F) for R-123, implying a small added margin for the latter. Second, the probability of a rupture or rapid release when fone occurs is lower, particularly if it occurs on the suction side of the compressor, which is below atmospheric pressure during normal operation. Spills or leaks still pose a threat in a warm room or if the liquid refrigerant reaches a warm surface. Similarly, the slower vaporization may lead to prolonged occurrence of low concentrations, if not detected and corrected, whereas a high pressure fluid will vaporize and be removed more rapidly through ventilation. The simple answer is that neither low nor high pressure refrigerants are risk-free. R-123 versus R-11. A more instructive comparison is between the alternative refrigerants and those they replace. Contrasting R-123 with R-11 shows the alternative refrigerant to be much safer in some respects, particularly for acute toxicity indicators. ‘The 4-hour LC50 (lethal concentration by inhalation) for rats Is nearly 25% higher; the cardiac sensitization level Is four times as high. As indicated in Table 2, these concentrations are 32,000 and 20,000 ppm for R-123, and 26,200 and 5,000 ppm for R-11. The concentrations at which anesthetic effects were observed in rats, for 10 minute exposures, were 40,000 ppm for R-123 as contrasted to 35,000 ppm for RL. The recommended exposure limit for chronic (long-term, repetitive or sustained) exposures to R-123 is much lower, 10 to 30 ppm time-weighted average (TWA), as discussed above. Actual concentrations were measured in two separate studies of 17 machinery rooms.{21,22] Both studies included some machinery rooms that do not satisfy minimum installation requirements. http://www.trane.com/commercial/issues/environmental/cfo6k.asp 4/29/2006Refrigerant Safety - Application Considerations Page 2 of 4 ‘The results of these studies are compared to the recommended exposure limits in Figure 1. The maximum measured concentrations are shown by the heights of bars labeled routine, transfer and leaks. They refer to concentrations during normal operation, during refrigerant transfer (charging and removal for two sites in one study and four in the other), and in the presence of Identified leaks (discussed below). Figure 1. Measured machinery room concentrations for R- 123 compared to recommended occupational exposure limits, [21,22] (The limits recommended by individual chemical manufacturers range from 10 to 30 ppm.) © James M, Calm, 1993 The highest concentration measured (following recommended handling and service procedures) was 0.64 ppm on a TWA basis. The range of recommended limits, from 10 ppm (shown in green) to 30 ppm (in white), are 15 to 45 times higher. ‘Concentrations as high as 2.5 and 13.6 ppm were measured two sites, in the vicinity of improperly sealed R-123 drums in one and with a leaking purge vent line and refrigerant drum in the other. The purge vent leak resulted from use of an incompatible material. Measurements repeated at the second site, after correction of the leaks, found a maximum of 0.56 ppm. These findings underscore the importance of proper installation, handling and storage procedures. A further study was performed to measure concentration excursions during internal maintenance on R-123 chillers, again following recommended installation and service practices, The maximum worker exposure, for short intervals, was found to be less than 2 ppm TWA; typical values were less than 1 ppm.[23] The American Conference of Governmental Industrial Hyglenists (ACGIH) recommends that worker exposure limits, for chemicals for which specific short-term exposure limits have not been set, exceed neither three times the TWA limit for 30 minutes nor five times the TWA limit Instantaneously.[24] For R-123, that translates to 30 or 90 ppm for 30 minutes, depending on which manufacturer's recommendation is used, and 50 or 150 ppm instantaneously. One manufacturer has set a short-term, emergency exposure limit for R-123 of 1,000 ppm for up to 60 minutes, with a ceiling (not to be exceeded) of 2,500 ppm for 1 minute. Figure 2 contrasts the measured worker exposures[23] (in grey) to the recommended short-term limits (in green). The dark green bars labeled EEL show the emergency exposure limit recommended by the manufacturer producing the largest quantity of R-123. The split bar labeled OEL, in light green, reflects the range of occupational exposure limits recommended by different chemical manufacturers. The http://ww.trane.com/commercial/issues/environmentaVcfe6k.asp 4/2912006Refrigerant Safety - Application Considerations Page 3 of 4 recommended short-term limits, also in light green, are those just discussed. Figure 2. Measured worker exposures during internal service compared to recommended exposure limits.[23] © James M. Calm, 1993. ‘Once again, none of the exposures during service operations reached the recommended limits. Moreover, the highest ‘exposures measured tended to be for much shorter durations than specified in the limits. A separate study of single chiller during servicing found TWA levels of 2 to 5 ppm, but with significant deviations. Floor- level concentrations reached 500 ppm for two intervals of several minutes during the most severe operations; corresponding excursions in the breathing zone were 80 and 100 ppm. One reason for the high concentrations is that the exhaust fans, which had been set to operate at 10 ppm, were reset to 500 ppm for this test.[25] Additional concentration data have been reported by a refrigerant manufacturer, based on conversions of its own equipment from R-11 to R-123. The conversions and monitoring were performed with participation of the three original equipment manufacturers for the chillers involved. Typical concentrations of 1 to 2 ppm were measured, even during refrigerant removal and recharging. Spikes of 8 to 20 ppm occurred, notably when making or breaking hose connections. [26] Based on these data, the margin of safety appears to be substantial, provided that recommended practices are followed. EPA summarized its assessment as follows: -EPA has conducted extensive industrial hygiene evaluations of typical industrial chiller installations and has found that chronic employee time weighted average ‘exposures are below 1 ppm. The level (recommended ‘occupational exposure limit) set by manufacturers Is 10 ppm. By following the appropriate monitoring procedures and safe handling of refrigerant, EPA believes that HCFC- 123 can be safely used in centrifugal chillers.[27] R-134a versus R-12. R-134a Is the primary replacement for R-12 in chillers and most other applications. It offers a 50% Increase over the already high cardiac sensitization level of R-12, 75,000 and 50,000 ppm, respectively. The concentrations at which anesthetic effects were observed in rats were 205,000 ppm for R-134a for 4-hour ‘exposures, as contrasted to 254,000 ppm for R-12 for much shorter, 10-minute exposures. Both the cardiac sensitization response and anesthetic effect levels are far above concentrations normally encountered. R-134a Is being considered as a pharmaceutical propellant for metered dose inhalers, an application requiring http://www trane.com/commercial/issues/environmental/efc6k.asp 4/29/2006Reftigerant Safety - Application Consider Page 4 of 4 extremely low toxicity levels. Based on current toxicity data, R-134a is regarded as one of the safest refrigerants yet introduced, ‘Comparison findings. The primary conclusion from these comparisons is that the alternative refrigerants can be used with comparable or higher safety than those they replace, especially for the most life-threatening risks under emergency conditions. After more than 50 years of wide use, with few incidents of injury or death, R-11 and R-12 have gained acceptance as being reasonably safe. The comparative data suggest that R-22, R-123 and R-134a can be as safe or safer. Ammonia also can be used safely, but requires additional precautions and has the advantage of being self-alarming. Table 2. Safety Indicators for Common Chiller Refrigerants Return to the Table of Contents “The Trane Advantage : Employment : Merchandise Shop : Just For Suppers Commercial Contact = Resider © 2006 Americ http:/Avww.trane.com/commercial/issues/environmental/cfe6k.asp 4/29/2006COMPRESSORS 07/96 _CB-232 WHAT HAPPENS IF.... What happens if a valve in the compressor discharge line is closed or restricted and no safety relief valve is present? One or more of the following will occur: ‘+ The discharge pressure will rise causing the horsepower to rise, The motor will ‘overload and trip out, + The discharge pressure will rise causing the discharge temperature to rise. The high discharge temperature will cause failure of the piston rings, valves, and packing, + The discharge pressure will rise until the compressor’s volumetric efficiency limit is reached. This could result in a discharge pressure of about 15 times suction pressure (higher for two-stage units). + The discharge pressure will rise and the weakest component will fail. Predicting which event will occur first or how quickly they will develop is diffi ‘System piping, the gas, vapor pressure, ambient temperature, motor size and wiring, and the general condition of the compressor will all have an effect. Assume that both pressure and temperature will be well above the maximum limits of the compressor if this situation occurs. Obviously a relief valve must be installed in the discharge line of every Blackmer compressor to prevent a hazardous or expensive failure. A relief valve should also be considered at the first stage discharge of two-stage compressors. Here are other items to consider: + Periodically check the relief valve (and other system components) to ensure that they are functioning properly. ‘* Install a second relief valve set at a pressure slightly higher than the primary relief valve. (Rupture disks may be used for this purpose but seldom are since they will not reseat when the pressure falls to normal values.) «Install a pressure switch in the discharge line set at a pressure below the relief valve setting. In this case the pressure switch will trip before the relief valve, providing a signal to stop the compressor. If the pressure switch fails, the relief valve will then open. «Install pressure gauges to monitor system pressures. * In addition to the above devices, a high discharge temperature switch and properly sized motor overload heaters will provide some protection. wewnblackmor.compage 2 07/96 CB-232 What happens if the compressor is allowed to run beyond the normal vapor recovery point? One or more of the following will occur: + The suction pressure will decrease causing the compression ratio and discharge temperature to rise, High discharge temperature will cause failure of the piston rings, valves, and packing. + The suction pressure will decrease until the volumetric efficiency limit of the compressor is reached. For a single stage compressor, the suction pressure could fall to as little as 7% of the discharge pressure (15 compression ratios). Two- stage compressors can reduce the suction pressure even further. ‘© The suction pressure may fall below atmospheric pressure. A single-stage ‘compressor may reduce the suction pressure to as little as 0.23 bara (3 psia) depending on the discharge pressure. «The suction pressure may fall below atmospheric pressure and the crankcase oil will be drawn into the cylinder. If enough oil is lost, the bearings will fail. + The suction pressure may fall below atmospheric pressure and air may be drawn into the cylinder (if the compressor is not fitted for vacuum suction conditions), possibly creating an explosive mixture. «The suction pressure may fall below atmospheric pressure, preventing draining of liquid from liquid traps. The liquid may then accumulate to excessive levels and enter the compressor. Predicting which situation will occur first or how quickly it will develop is difficult. System piping, the gas, vapor pressure, ambient temperature, motor size and wiring, and the general condition of the compressor will all have an effect. The maximum discharge temperature during this type of operation will vary tremendously. Assume that the temperature will rise above the 177°C (350°F) rating of the compressor. ‘Also assume that the suction pressure will eventually fall below atmospheric pressure, The point at which the Vapor Recovery process ‘ends’ is seldom precisely defined and often changes depending on the ambient temperature. Missing it slightly is usually no cause for concer as the scenarios listed above will take some time to develop. Here are some items to consider: © Proper training of personnel in the system's operation, + Always have trained personnel present during transfer operations (this is a requirement in NFPA #58). + Install a low suction pressure switch. Set the switch to trip when the suction pressure falls to near atmospheric pressure if this is to be used as a backup alarm or shutdown device. If this switch is to be used to signal the ‘end’ of the vapor recovery operation, change its setting depending on the season. Install a timer to stop the compressor after a preset time of operation. Install a high discharge temperature switch. A low oil pressure switch may prevent expensive damage to the compressor. Install pressure gauges to monitor system pressures. eww blackmer.compage 3 07/96 CB-232 What happens if liquid enters the trap, the trap’s float rises to block the compressor suction and the compressor continues to run? or What happens if the suction line is blocked by a closed valve or clogged strainer and the compressor continues to run? One or more of the following will occur: ‘* The suction pressure may fall below atmospheric pressure and the crankcase oil will be drawn into the cylinder, if enough oil is lost, the bearings will fal. ‘+ The suction pressure will decrease causing the compression ratio and discharge temperature to rise. High discharge temperature will cause failure of the piston rings, valves, and packing, * The suction pressure will decrease until the volumetric efficiency limit of the compressor is reached. For a single stage compressor, the suction pressure could fall to as little as 7% of the discharge pressure (15 compression ratios). Two- stage compressors can reduce the suction pressure even further. © The suction pressure may fall below atmospheric pressure, A single-stage compressor may reduce the suction pressure to as little as 0.23 bara (3 psia) depending on the discharge pressure. ‘+ The suction pressure may fall below atmospheric pressure and the crankcase oil will be drawn into the cylinder. If enough oil is lost, the bearings will fal. + The suction pressure may fall below atmospheric pressure and air may be drawn into the cylinder (if the compressor is not fitted for vacuum suction conditions), possibly creating an explosive mixture. Damage to the rings, valves and packing due to temperature and loss of crankcase oil due to the very low suction pressure can start quickly since the volume of the suction piping is so small in this situation. Fortunately, the sound of the compressor and the falling suction pressure are clear signals to the operator. Here are additional items to consider: ‘* Proper training of personnel in the system's operation, * Always have trained personnel present during transfer operations (this is a requirement in NFPA #58). ‘+ Install liquid tevel switch in the trap to stop the compressor in the event of high liquid level. ‘+ Install a low suction pressure switch between the trap and the compressor, Set the switch to trip when the suction pressure falls near atmospheric pressure. * Install a low oil pressure switch to stop the compressor before extensive damage occurs, + Install a high discharge temperature switch to stop the compressor or sound an alarm, * Install pressure gauges to monitor system pressures. wir. blackmer comforum WHAT IS THE OPTIMUM COMPRESSOR DISCHARGE PRESSURE SET POINT FOR CONDENSERS? Dr Richard J. Love, Prof, Don J. Cleland, Or Inge Merts, Mr Brett Eaton Centre for Postharvest and Refrigeration Research Massey University, Palmerston North, ABSTRACT Optimisation of condenser set points lo ininiso enexy use roquros radool tween high compressor energy use a high hood ‘pressures ane high condonser fan and pump energy we to achieve low head pressures. Is shown tha for most condonser sections ‘eed in New Zealand indus appctions,Realing the oad pressursthe best stalegy. Mulispood fae and varable spent dave {VSO} fan contcs ont give siaiicant eneray use reductions compared with oral coil compressors operate highly urloaded andlor ‘the condenser ie grossly versed, Ol saparators, decharge and high pressure quid ines, ant expansion and ole etigeart contot ‘vals souk be desiod to operate salstactrty across the tl range of lechary pressures key o bo oncounlored f charge resto sted, Keywords: condonsor, onargy use, presse, comoressor 1- Introduction Most instil ofigoraton systems employ compressor echarge thd) presoue conve. Gonerly these conto moduiate the condense ans (ora cooked or evaporative condoneors) o wale fw ales and coolng towor fans (or vatercodled condensers to kao the head pressure win 2 spectod range. Radin fan speed or cooly wate ow reduces the olecine capaty of the condeneers eo that it {cua the requiod Moat telat by maintaining a erger temporatvedferonco botween th rtigerant saturated cndersation temperature (SCT) andthe embiont wt but> {8 tompacatre, Tho compressor discharge pressure ‘aust o equal the prossurocorrespending tothe SCT ph th discharge ne pressure kop and the paral pressure of sary non-condensable aces posentin tho retigoent. For “mpi, ils common practic to expres comprcesor Carrler Corporation Syracuse, New York October 2005,INTRODUCTION ‘Today's building owners and managers requite well-engineered solutions to keep long-term opera- tional costs under control. The ability to lower heating and cooling costs is critical to this goal. The ‘American Society of Heating, Reftigeration and ‘Air-Conditioning Engineers (ASHRAE) estimates that 50% of all building energy is consumed by HVAC operation. VARIABLE FREQUENCY DRIVES ‘Variable frequeney drives (VFDs) prevent wasting energy by precisely matching motor speed with ‘cooling requirements, which results in dramatic reductions in power usage. Affordable and factory installed in most cases, VEDs are one of the most cost-effective ways to maximize efficiency and reduce operating costs. According to ARI (Air Conditioning and Refrigeration Institute) Standard 550/590-2003, chillers typically run 99% of the time at part-load (off design conditions). ‘Therefore, having your chiller match your building’s load profile will pro- vide both efficiency and comfort, To date, varinble speed centrifugal compressors have been the best means to effectively reduce ener- gy consumption during the majority of the opera- tional hours. When variable speed is applied to a sorew compressor, the savings are increased, since the variable speed screw chiller always provides the maximum amount of speed reduction, In order to fully appreciate the benefits of variable speed screw water-cooled chillers, an understanding of centrifugal water-cooled chillers is required. CENTRIFUGAL COMPRESSORS Centrifugal air compressors had been in use for 75 years when, in 1916, Dr. Willis HI. Carrier recog- nized their potential for air conditioning applica- tions. Carrier sold the first water-cooled centrifugal chiller in 1924 to the Onondaga Pottery Company in Syracuse, New York. The machine ran for 26 years and provided air conditioning throughout that peri- ‘od. The compressor of that first machine was retired to the Smithsonian Institute in Washington, D.C., where it remains as one of the major technical developments in the history of the United States. Centrifugal compressors are dynamic compression devices that continuously exchange angular momentum between a rotating impeller and steadily flowing refrigerant. As refrigerant molecules are accelerated outward by centrifugal force, new ones are drawn into the compressor to replace them. The overall effect is one of continuously compressing a stream of reftigerant. (Figure |.) Fig. 1. Centrifugal compressor inpeller and diffuser: Centrifugal compressor performance can be modeled by the following ideal fan laws,Ideal Fan Laws Law Flow Rate, FlowRate, x nen Law2 : Ute Lit, x (sei) Law3 Power;=-Power, x{ SMa RPM, Lift Lift is defined as the difference between the con- densing (discharge) pressure and the evaporating (suction) pressure. Therefore, lif, or the amount of ‘work the compressor performs on the refrigerant, is dependent on the leaving chilled water temperature and condenser water temperature. The compressor only experiences full lift conditions when the wet bull temperature is at design and refrigeration load is 100%. As the wet bulb temperature decreases, the cooling tower provides colder condenser water to the chiller, reducing the lift required of the com- pressor. (Figure 2.) In addition, reductions in load will reduce lift because lower saturated condensing pressure result when less heat is rejected to the condenser. A vati- able speed chiller responds to changes in lift and reftigeration load by adjusting speed. ‘As demonstrated by the ideal fan laws, a reduction in speed of the centrifugal compressor will have an ‘exponential (cubic) decrease in compressor power consumption. Given this fact, it is no surprise that to ate, variable speed centrifugal compressors have been the best means to effectively reduce energy ‘consumption during the majority of the operational hours. ith 65 F entering condenser water, Lift=77F - 42 F Pig, 2. Pressure enthalpy chart WHY INLET GUIDE VANES ARE USED IN VARIABLE SPEED APPLICATIONS The most common form of capacity control for con- stant speed centrifugal chillers is to modulate guide vanes at the impeller inlet (also called pre-rotation vanes). As load is decreased, the mass flow of refrigerant moving through the compressor must be reduced. On constant speed machines, the guide vanes are closed to match compressor capacity to the load. When centrifugal machines are equipped with VFDs, speed control can also be used to con- trol capacity. In this case, the impeller speed can be reduced to match the compressor capacity to the Toad. ‘RPM, J Lifts Lift, (setRecalling that the lift produced by a centrifugal ‘compressor is also reduced when speed is reduced, we can determine that speed adjustment alone can- not always be used to regulate the variable speed centrifugal chiller. Under certain lift conditions, the speed is reduced as much as lift requirements will allow and then guide vanes are used to complete the load reduction. Mechanical unloaders of any kind introduce inefficiency. So while speed reduction is almost always obtained with any reduction of lit or load requirements, the question becomes one of magnitude. The amount of capacity reduction per- formed by speed reduction, relative to the amount of capacity reduction performed by guide vanes is an indication of the centrifugal chillers ability to capture all theoretical savings at a given operating point. Conversely, the more the guide vanes are closed, the higher the amount of inefficiency intro- duced into the system, Given the cubic relationship of speed and power even a small amount of speed reduction yields a sig- nificant reduction in energy. However, the more speed reduction possible, the greater the energy savings. UNDERSTANDING SCREW COMPRESSORS Heinreich Krigar of Germany developed the first screw compressor in 1878. In the early 1930's, a ‘Swedish engineer by the name of Alf Lysholm developed the profile of the modern screw compres- sor for gas and steam turbine applications. Screw ‘compressors have been used in HVAC applications for neatly three decades. (Figure 3). ‘The screw compressor is classified a positive dis- placement compressor, which simply means that a volume of gas is trapped with an enclosed space whose volume is then reduced, Conventional rotary ‘screw compressors are composed of two parallel rotors with external helical profiles fit into a casing. (Figure 3.) One of the rotors is coupled to the motor (drive rotor) and as it turns it moves the other rotor (driven rotor), similar to a common gear set. The ‘geometric profile of the rotating rotors is difficult to Fig. 3. Conventional iin serew compressor. visualize, It is easier to relate the compression process to a reciprocating compressor, if you con- sider the drive rotor as the piston and the driven rotors as the cylinder. As the drive rotors and driven rotors unmesh, an empty cylinder is created, draw- ing in suction gas through the synchronized opening on the rotor suction face. As rotation continucs, the suction and discharge rotor faces are sealed off, trapping the gas in the cylinder. When this happens, the meshing point moves toward the discharge end of the rotors and drives the gas ahead of it, The dis- charge port provided for the gas escape is relatively small, compared to the suction port, resulting in pos- itive displacement compression. Rotary serew compressors are well known for their robustness, simplicity, and reliability. They are ed for long periods of continuous operation, needing very little maintenance. Serew compressors can overcome high lift when speed is reduced, allowing energy savings without the possibility of surge as the compressor unloads. VARIABLE SPEED SCREW COMPRESSORS For positive displacement compressors, speed is independent of lift, or worded another way, the compressor can develop the same amount of lift at any speed. Therefore, mechanical loaders can be replaced entirely by speed control. As discussed carlier, centrifugal compressors may require speed control coupled with some closure of the inlet guide vanes, The variable speed screw compressor never has to temper speed control with a guide vane or slide valve, and therefore captures the maximum.