HVAC ECBC Tip Sheet
HVAC ECBC Tip Sheet
HVAC ECBC Tip Sheet
HVAC SYSTEM
five thousand years ago and developed to Thermostats and controls should accommodate
load reduction. Insulating the roof helps
decrease heat conduction to the
an impressive level of maturity. However, inside of the building
the invention of refrigerative chiller by Green roofs help in lowering the Roof
Temperature Structural overhangs,
Willlis Haviland Carrier in 1902 changed lightshelves reduce solar
gain
duction should be approached in con- the evaporator and the condenser. The Water
cert with whole-building load reduction pump forces the refrigerant through the Chiller
11%
measures for both cooling and heating circuit of tubing and fins in the coils. Ducted/
systems. The objectives of saving cooling The liquid refrigerant evaporates in Package
AC 19%
and heating energy may be in conflict or the evaporator coil, pulling heat out of Room AC
69%
may support each other. For example, bet- indoor air and thereby cooling the space.
ter insulation and high insulation win- The hot refrigerant gas is pumped into
dows can reduce both loads while light- the condenser where it reverts back to a
ing load reductions may increase heating liquid giving up its heat to the air flowing Fig. 2: Market Share of Different Types
of AC Units in India (Source: 2007 Sales
loads. High-performance windows may over the condenser’s metal tubing and Data Emerson Climate Technology)
be the last step needed in eliminating part fins. Because the condenser is the heat
or all of the perimeter HVAC equipment, rejection unit so it should be located in split-system air-conditioners, this indoor
while providing superior radiant comfort such a manner that the heat sink is free of cabinet also contains a furnace or the
in both summer and winter. interference from heat discharge of other indoor part of a heat pump.
To take advantage of load variations, it equipment for optimum performance.
is critical that building mechanical systems Packaged air-conditioners: In a packaged
be capable of reacting to the reduced loads. Type of Air-Conditioners air-conditioner, the evaporator, condenser,
This requires variable capacity pumps The most common types of air-conditioners and compressor are all located in one
and fans (or variable capacity compressor are room air-conditioners, split-system cabinet, which usually is placed on a
and condenser units in case of packaged central air-conditioners, packaged air- roof or on a concrete slab adjacent to the
or split-systems) and reliable sensors and conditioners, and central air-conditioners. building. This type of air-conditioner is
controls to allow the equipment to power Fig. 2 shows market share of different types typical in small commercial buildings
down when loads drop. of vapor compression HVAC technologies and also in residential buildings. Air
(residential and commercial) in India. supply and return ducts come from
Air-Conditioner Basics indoors through the building’s exterior
Air-conditioners employ the same Room and split air-conditioners: Room wall or roof to connect with the packaged
operating principles and basic components air-conditioners cool rooms rather than air-conditioner, which is usually located
as a refrigerator. An air-conditioner the building. They provide cooling only outdoors. Packaged air-conditioners often
cools with a cold indoor coil called when needed Room air-conditioners are include electric heating coils or a natural
the evaporator. The condenser, a hot less expensive to operate than central gas furnace. This combination of air-
outdoor coil, releases the collected heat units, even though their efficiency is conditioner and central heater eliminates
outside. The evaporator and condenser generally lower than that of central air- the need for a separate furnace indoors.
coils are serpentine tubing surrounded conditioners.
by aluminum fins. This tubing is usually In a split-system central air-conditioner, Central air-conditioners: In Central
made of copper. A pump, called the an outdoor metal cabinet contains the air-conditioning systems, cooling is
compressor, moves a heat transfer fluid condenser and compressor, and an indoor generated in a chiller and distributed
(or refrigerant such as ammonia and cabinet contains the evaporator. In many to air-handling units or fan-coil units
with a chilled water system. This category
Table 2: Thermal Comfort Parameters (Source: Fanger, 1970) includes systems with air-cooled chillers
Parameters Significance Design/IEQ Implications as well as systems with cooling towers for
Air Most important parameter for Determines thermostat set points, sensible heat rejection (see text box on page 8 for
Temperature determining thermal comfort loads and influences the perception of In- detailed discussion).
door Environmental Quality (IEQ)
Mean Radiant Key factor in the perception of Radiant panels can reduce the requirement Heating System Types
Environmental
Temperature thermal discomfort resulting of conditioned air Heating system types can be classified
from radiant asymmetry
fairly well by the heating equipment type.
Relative Excessive dry or humid condi- Enthalpy-based economizer, although
Humidity tions are immediately perceived difficult to control has good potential to
The heating equipment used in Indian
as uncomfortable save energy and provide greater thermal commercial buildings include boilers (oil
comfort and gas), furnaces (oil, gas, and electric), heat
Air Velocity Key factor in the perception of Can be used to reduce thermal discomfort pumps, and space heaters.
draft due to elevated air velocity in conjunction with passive design Boiler-based heating systems have steam
and/or water piping to distribute heat. The
Activity Level Poses a problem to designers if Determines thermal output of individu-
an indoor space has to be de- als which directly affects cooling/heating heated water may serve preheat coils in
signed for people with different load of a conditioned space air handling units (see text box on page 5),
activity levels reheat coils, and local radiators. Systems
Personal
Clothing Important factor in the percep- In office environment, chair upholstery that circulate water or a fluid are called
Resistance tion of thermal comfort; use of can increase the resistance by as much as hydronic systems. Additional uses for the
clothing to adjust to thermal en- 0.15 clo; difference in the clo values of heating water are for heating of service
vironment is a good example of male and female dresses should be taken
water and other process needs, depending
adaptive control. into account while designing indoor envi-
ronment on the building type. Some central systems
have steam boilers rather than hot water
Air System Balancing: Adjusting circulation, air cleaning, dehumidifying, The weighting factors have been based
airflow rates through air distribution or humidifying. on the weighted average of the most
system devices, such as fans and diffusers, common building types and operation
by manually adjusting the position of Hydronic System Balancing: Adjusting using average weather in 29 U.S. cities,
dampers, splitter vanes, extractors, etc., water flow rates through hydronic with and without air side economizers.
or by using automatic control devices, distribution system devices, such as
such as constant air volume or variable pumps and coils, by manually adjusting Return Air: Air from the conditioned
air volume boxes. the position of valves, or by using area that is returned to the conditioning
automatic control devices, such as flow equipment for reconditioning. The air may
Boiler: A self-contained low-pressure control valves. return to the system through a series of
appliance for supplying steam or hot ducts, plenums, and airshafts.
water. A packaged boiler includes factory- kW/ton Rating: Commonly referred to
built boilers manufactured as a unit or as efficiency, but actually power input Seasonal Energy Efficiency Ratio
system, disassembled for shipment, and to compressor motor divided by tons (SEER): SEER is a measure of equipment
reassembled at the site. of cooling produced, or kilowatts per energy efficiency over the cooling season.
ton (kW/ton). Lower kW/ton indicates It represents the total cooling of a central
Coefficient of Performance (COP): higher efficiency. air-conditioner or heat pump (in kWh)
Chiller efficiency measured in Btu output during the normal cooling season as
(cooling) divided by Btu input (electric Integrated Part-Load Value (IPLV): compared to the total electric energy input
power). Multiplying the COP by 3.412 This metric attempts to capture a more consumed during the same period.
yields the energy-efficiency ratio. representative “average” chiller efficiency
over a representative operating range. It Supply Air: Air being conveyed to a
Constant Volume System: A space- is the efficiency of the chiller, measured conditioned area through ducts or plenums
conditioning system that delivers a in kW/ton, averaged over four operating from a heat exchanger of a heating, cooling,
fixed amount of air to each space. The points, according to a standard formula. absorption, or evaporative cooling system.
volume of air is set during the system Supply air is commonly considered air
commissioning. Outdoor Air : Air taken from outdoors and delivered to a space by a space-conditioning
not previously circulated in the building. system. Depending on space requirements,
Economizer, Water-side: A system by For the purposes of ventilation, outdoor the supply may be either heated, cooled or
which the supply air of a cooling system is air is used to flush out pollutants produced neutral.
cooled indirectly with water that is itself by the building materials, occupants and
cooled by heat or mass transfer to the processes. Tons: One ton of cooling is the amount
environment with the use of mechanical of heat absorbed by one ton of ice melting
cooling. Part-Load Performance: For Water in one day, which is equivalent to 12,000
chilling packages covered by this Btu/h or 3.516 thermal kW.
Economizer, Air-side: A duct and standard, the IPLV shall be calculated as
damper arrangement and automatic follows: Variable Air Volume (VAV) System: A
control system that together allow a Determine the part-load points. Use the space conditioning system that maintains
cooling system to supply outdoor air to following equation to calculate the IPLV. comfort levels by varying the volume of
reduce the need for mechanical cooling conditioned air. This system delivers
during mild or cold weather. IPLV = 0.01A+0.42B+0.45C+0.12D conditioned air to one or more zones. The
duct serving each zone is provided with a
Energy-Efficiency Ratio (EER): For COP and EER: motorized damper that is modulated by a
Performance of smaller chillers and Where: A=COP or EER at 100% signal from the zone thermostat.
rooftop units is frequently measured B=COP or EER at 75%
in EER rather than kW/ton. EER is C=COP or EER at 50% Zone: A space or group of spaces within
calculated by dividing a chiller’s cooling D=COP or EER at 25% a building with heating and cooling
capacity (in Btu/h) by its power input (in requirements that are sufficiently
watts) at full-load conditions. The higher For kW/ton: similar so that desired conditions
the EER, the more efficient the unit. IPLV: (e.g., temperature) can be maintained
1 throughout using a single sensor (e.g.,
Heat Pump: A heat pump consists of 0.01 0.42 0.45 0.12 thermostat or temperature sensor).
one or more factory-made assemblies that + + +
A B C D
normally include indoor conditioning coil,
compressor, and outdoor coil, including Where:
means to provide a heating function. Heat A=kW/ton at 100%
pumps provide the function of air heating B=kW/ton at 75%
with controlled temperature, and may C=kW/ton at 50%
include the functions of air cooling, air D=kW/ton at 25%
as multiple zone air and water systems. and humidity are mild, economizers save Return Air
Motorized
Actuator
The more complex the system, the more energy by cooling buildings with outside
requirements apply to that system: a air instead of by using refrigeration Fig. 4: The Components of an Economiz-
single-zone unitary system has fewer equipment to cool recirculated air. er (Source: E Source Cooling Atlas)
Evaporative Cooling air can be used in HVAC applications • Ground-source closed-loop heat pumps
Evaporative cooling is an ancient air to reduce cooling loads, improve chiller (GSHPs) system use a pump and ground-
conditioning technique that is growing efficiency, and widen the applicability coupled heat exchanger to provide a heat
in popularity due to increased interest in of evaporative cooling, while providing source and heat sink for multiple GSHPs
energy efficiency, reduced peak demand, improved indoor air quality and within the building.
improved indoor air quality, and non- eliminating the use of CFC refrigerants.
CFC cooling. Evaporative cooling In combination with evaporative Absorption Cooling
typically uses less than one-fourth cooling, desiccant cooling can eliminate On the surface, the idea of using an
the energy of vapor-compression air- refrigerative air conditioning in many open flame or steam to generate cooling
conditioning systems, while using no climates. might appear contradictory, but the
more water than a power plant uses to A conventional cooling system idea is actually very elegant. Instead
produce the electricity needed for the same dehumidifies bypassing the supply of mechanically compressing a gas
amount of vapor-compression cooling. air across a cooling coil that is cold (as occurs with a vapor-compression
The cost of an evaporative cooling system enough to condense water vapor. This refrigeration cycle), absorption cooling
may be higher than a vapor compression dehumidification requires a colder coil relies on a thermochemical “compressor.”
chiller system, but payback is typically than would be required for sensible cooling Absorption cooling is more common
1-5 years depending on climate. alone, often doubling energy requirements today than most people realize. Large,
The most common type of direct at typical low-load conditions where it is high-efficiency, double-effect absorption
evaporative cooler uses a cellulose fiber necessary to dehumidify but not cool. chillers using water as the refrigerant
pad, permeable to both water and air, Often in these conditions, the air is cooled dominate the Japanese commercial air-
which has water pumped into its top edge. for dehumidification and then must be conditioning market. While less common
As the air passes through the wetted pad, reheated for comfortable supply. With in India, interest in absorption cooling
water evaporates, taking heat from the air, desiccants, dehumidification takes place is growing, largely as a result of high
and the air cools adiabatically to balance independently of sensible cooling. In large electricity tariffs and growing availability
the heat it has lost to evaporation. buildings, desiccants can reduce HVAC of natural gas on a commercial basis.
Indirect evaporative coolers (see Fig. 5) electricity use by 30-60 %. Fig. 6 shows Absorption cooling is most frequently
eliminate the problem of increasing the how the desiccant wheel alternately passes used to air-condition large commercial
moisture content of the air that enters through two separate airstreams; one to buildings. Absorption cooling equipment
the conditioned space by using a heat be dehumidified and used in the building, on the market ranges in capacity from
exchanger. In an air-to-air heat exchanger and one to regenerate the desiccant with less than 10 tons to over 1,500 tons (35 to
system, secondary (exhaust) air flows warm, dry air. 5,300 kW). Coefficients of performance
through one side of the heat exchanger range from about 0.7 to 1.2, and electricity
where it is sprayed with water and cooled Desiccant Wheel
Dehumidified use ranges from 0.004 to 0.04 kW/ton of
Supply Air
by evaporation. The building supply air cooling. Absorption chillers may make
flows through the other side of the heat Outside Air sense in the following situations:
exchanger where it is sensibly cooled • Electric demand charges are high
by the evaporative cooled secondary • Electricity use rates are high
air. Because of the heat exchanger, the Heater
• Natural gas prices are favorable
effectiveness of indirect evaporative • Utility and manufacturer rebates exist
cooling is reduced to about 65-75 %, but it To Outside Partition separates heated
exhaust air from supply air
The potential of absorption cooling
has wider applicability to climates where systems to use waste heat can greatly
Fig. 6: Solid Desiccant Wheels (Source:
increased air humidity is unwelcome. E Source Cooling Atlas) improve their economics. Indirect-fired
Secondary Air chillers use steam or hot water as their
Secondary
air Fan
Wetted pad of other direct
evaporating media Ground Source Heat Pump: primary energy source, and they lend
Water-loop heat pump (WLHP) themselves to integration with on-site
systems have captured a small (3 to 4%) but power generation or heat recovery from
Heat Exchanger slowly growing percentage of the U.S. incinerators, industrial furnaces, or
Conditioned air
commercial cooling market and have manufacturing equipment. Indirect-fired,
good potential in India as well. double-effect absorption chillers require
Outdoor Air
Ground coupled systems provide steam at around 190° C and 900 kPa, while
passive heating and cooling by using the the less efficient (but also less expensive)
Supply Fan
ground as a heat source or a heat sink. single-effect chillers require hot water or
There are two basic varieties. steam at only 75-132 ° C. High-efficiency,
Pump Reservoir • Groundwater-source heat pumps double-effect absorption chillers are more
Fig. 5: Indirect Evaporative Cooler (GWHPs) draw water from wells, lakes, expensive than electric-driven chillers.
(Source: E Source Cooling Atlas) or other reservoirs of groundwater, pass They require larger heat exchangers
Desiccant Heat Recovery the water through an open loop, and because of higher heat rejection loads; this
Properties of desiccants materials to discharge it back to the environment. translates directly into higher costs.
readily attract water and thus dehumidify
Overview (US DOE, 2008) as possible while meeting the occupants’ TAB function is to help the system to work
Building commissioning is a systematic comfort and functional needs throughout properly by balancing the fluid flows to
process of ensuring that a building the life of the building. It is worth their correct proportion and in the process
performs in accordance with the design noting that Continuous commissioning identify design and installation errors, if
intent, contract documents, and the is different from building operation and they exist, to ensure the performance of
owner’s operational needs. Due to the maintenance. the HVAC system. Some key issues that
sophistication of building designs and Benefits of building commissioning a firm undertaking TAB functions must
the complexity of building systems include: address are listed below:
constructed today, commissioning • Energy savings and persistence of
is necessary, but not automatically savings 1. Identification of a Traverse Location:
included as part of the typical design and • Improved thermal comfort with proper To ensure that accurate measurements
construction process. Commissioning environmental control of airflows inside ducts can be
is critical for ensuring that the design • Improved indoor air quality obtained. This information is then
developed through the whole-building • Improved operation and maintenance used by HVAC control system to
design process is successfully constructed with documentation regulate the flow of air and optimize
and operated. • Improved system function that eases system operation.
Building commissioning includes the building turn-over from contractor to
following: owner. 2. Determining Outside Air Quantity:
• Systematically evaluating all pieces If supply and return airflow are
of equipment to ensure that they are Commissioning Cost measured accurately, outside airflow
working according to specifications. Building owners are finding that could easily be determined from the
This includes measuring temperatures the energy, water, productivity, and following Equation:
and flow rates from all HVAC devices operational savings resulting from Qsupply = Qreturn +Qoutside
and calibrating all sensors to a known commissioning offset the cost of
standard. implementing a building commissioning 3. Duct Leakage: A good duct traverse
• Reviewing the sequence of operations to process. Recent studies in the U.S. can also be used to determine duct
verify that the controls are providing the indicate that on average the operating leakage.
correct interaction between equipment. costs of a commissioned building range
In particular, building commissioning from 8 to 20% below that of a non- 4. Determining Pump Flow: Like measuring
activities include: commissioned building. The one-time airflow on a fan, pump flow
• Engaging a commissioning authority investment in commissioning at the measurements can sometimes be
and team beginning of a project may result in suspect. Most TAB technicians will
• Documentation reduced operating costs that will last the determine flow by measuring the
• Verification procedures, functional life of the building. differential pressure between pump
performance tests, and validation The cost of commissioning is discharge and pump suction. By
• Training. dependent upon many factors including using the manufacturer’s pump curve
Commissioning HVAC systems is a building’s size and complexity, and and the pressure measurements, the
even more important in energy-efficient whether the project consists of new technician can estimate total flow.
buildings because equipment is less likely construction or building renovation. In
to be oversized and must therefore run general, the cost of commissioning a new 5. Sizing Balancing Valves: A balancing
as intended to maintain comfort. Also, building ranges from 0.5% to 1.5% of the device is similar to a control device
HVAC equipment in better performing total construction cost. For an existing and should be sized accordingly.
buildings may require advanced control building, never before commissioned, Balancing devices should be sized
strategies. Commissioning goes beyond the cost of retrocommissioning can range based on the design pressure
the traditional HVAC elements. More from 3% to 5% of the total operating cost. difference at that part of the system.
and more buildings rely on parts of the For HVAC and Control Systems, cost of
envelope to ensure comfort. commissioning ranges from 1.5 to 2.5% of 6. Fan and Pump Curves: Manufacturers’
Commissioning includes evaluating mechanical system cost. performance curves are graphic
the building elements to ensure that shade representations of measured
management devices are in place, glazing is Testing, Adjusting, and performance under laboratory
installed as specified, air-leakage standards Balancing (Nolfo, 2001) conditions. The combination of
have been met—these are the static Testing, Adjusting, and Balancing (TAB) field measurements and associated
elements of the building. Commissioning refers to the process whereby a system calculations can be plotted on the fan
can also evaluate other claims about the or a component must first be tested curve. If accurate, careful, thoughtful
construction materials such as Volatile to determine its operating state, then measurements can be taken, the
Organic Compounds (VOCs) emission adjusted, and finally balanced to produce measured data usually matches the
content and durability. the desired results and performance in published data within the normal
Continuous commissioning ensures accordance with the design documents. tolerances of the performance tests.
that the building operates as efficiently The primary objective of carrying out the
ing power.
Water-cooled chillers incorporate the
use of cooling towers which improve heat
rejection more efficiently at the condenser Air Water Refrigerant Water
Air
between the condenser water and cooling Fig. 7: Process Diagram of a Chilled Water Air-Conditioning (Source: E Source Cool-
air. For an air-cooled chiller, condenser ing Atlas)
fans move air through a condenser coil. As most efficient chiller for that application operate most efficiently under part-
heat loads increase, water-cooled chillers is the one with the lowest kW/ton at 60% load conditions that most chillers
are more energy efficient than air-cooled load, regardless of peak load kW/ton. spend most of their time satisfying
chillers. Chillers are getting more efficient
(typically 40 to 70% load).
Thanks to design advances, new chillers are far more
efficient than their predecessors, even though CFC -free
Type of Chillers refrigerants are less efficient than CFC refrigerants. 4. Maximize system efficiency: Cool-
Chillers are classified according to com- Typical chiller performance ing tower fans and condenser and
pressor type. Electric chillers for com- Standard High-efficiency chilled water pumps should be con-
mercial comfort cooling have centrifugal, 0.90 sidered along with chiller energy con-
screw, scroll, or reciprocating compres- 0.8
0.80
0.75
0.70 0.70
sumption. Chiller efficiency increases
0.65
sors. Centrifugal and screw chillers have 0.6
0.60 with higher-temperature chilled water
one or two compressors. Scroll and recip- 0.48
and lower-temperature condenser wa-
0.4
rocating chillers are built with multiple, ter (called lower “lift”).
smaller compressors. 0.2
• Centrifugal chillers are the quiet, ef- 0 5. Select unequally sized machines
pre-1973 1980 1990 1997
ficient, and reliable workhorses of com- Year manufactured for multiple chiller installations:
fort cooling. Although centrifugal chill- Fig. 8: Trend in Chillers Efficiency Select one machine small enough to
(Source: E Source Cooling Atlas)
ers are available as small as 70 tons, most meet light loads efficiently and the
are 300 tons or larger. others to meet larger loads efficiently.
• Screw chillers are up to 40% smaller and Top Issues to Consider When Start additional chillers only when
lighter than centrifugal chillers, so are Buying a Chiller the chillers that already are running
becoming popular as replacement chill- are near full capacity.
ers. 1. Plan ahead: It makes sense to start
• Scroll compressors are rotary positive- planning early to allow sufficient time 6. Obtain competitive bids: There are
displacement machines, also fairly new to evaluate various scenarios and to often good reasons to stay with the
to the comfort cooling market. These identify a comprehensive system ap- same brand of chiller—maintenance,
small compressors are efficient, quiet, proach which best meets budgetary other equipment in the facility, exist-
and reliable. Scroll compressors are made and facility needs. ing service relationships, etc. Howev-
in sizes of 1.5 to 15 tons. er, for such a major purchase it makes
2. Buy only as much chiller as you sense to obtain bids from more than
Chiller Efficiency need: Reduce building loads and one manufacturer. All manufactur-
Chiller efficiency is rated in kW/ton (or improve air-side distribution before ers have “sweet spots”—sizes at which
COP) for larger machines and EER or sizing the chiller. Buying more cool- their equipment is most efficient.
COP for smaller machines (see Fig. 8). ing than you need not only costs
Efficiencies are measured at peak load money for equipment, it also increases 7. Monitor the system on an ongoing
and at IPLVs. The concept of the “most monthly utility bills. basis: Monitor compressor power and
efficient chiller” makes sense only in con- cooling load to determine whether or
text of the facility to be cooled. If a chill- 3. Use computer simulations to model when attention will be needed, and to
er operates 90% of the time at 60% load the building throughout the year: allow optimal system operation.
and very rarely at 90-100 % load, then the Designs should include chillers that
Role of Temperature and Impact of IEQ on Health and filtration efficiencies vary among IAQ and
Humidity Productivity ventilation standards and guidelines.
The influence of the indoor thermal Some characteristics of the indoor
environment on thermal comfort is environment, such as temperatures and Maintain Min. Ventilation Rates
widely recognized. Even in laboratory lighting quality, may also influence The minimum ventilation rates specified
settings with uniform clothing and activity worker performance without impacting in the applicable code requirements
levels, it is not possible to satisfy more than health. In many businesses, such as should be maintained or exceeded. The
95% of occupants by providing a single office work, worker salaries plus benefits HVAC system should be designed so
uniform thermal environment (Fanger dominate total costs; therefore, very small that rates of outside air intake can be
1970) because thermal preferences vary percentage increases in productivity, measured using practical measurement
among people. Despite the significant even a fraction of one percent, are often techniques. In buildings with variable
attention placed on thermal comfort by sufficient to justify expenditures for air volume (VAV) ventilation systems,
building professionals, dissatisfaction with improvements that increase productivity. special controls may be needed to ensure
indoor thermal conditions is the most In a critical review and analysis of minimum outside air intake into the
common source of occupant complaints existing scientific information, Fisk and AHU is maintained during operation.
in office buildings (Federspiel 1998). Rosenfeld (1997) have developed estimates
Air temperature and humidity also of the potential to improve productivity Recirculation of Indoor Air
influence perceptions of the quality of in the U.S. through changes in indoor Recirculation of indoor air is standard
indoor air and the level of complaints environments. The review indicates that practice in some countries, such as India,
about non-specific building-related building and HVAC characteristics are and discouraged in other countries
health symptoms (often called sick associated with prevalences of acute such as those of Scandinavia. When air
building syndrome symptoms). Relative respiratory infections and with allergy and is recirculated, it should be filtered to
humidities below approximately 25% asthma symptoms and non-specific health remove particles. However, filters are
have been associated with complaints of symptoms. From analyses of existing often used only to prevent soiling and
dry skin, nose, throat, and eyes. At high scientific literature and calculations fouling of the HVAC equipment. These
humidities, discomfort will increase using statistical data, the estimated filters have a very low efficiency for
due substantially to an increase of skin potential annual nationwide (for the US) respirable-size particles (smaller than 2.5
moisture. The upper humidity limits of benefits of improvements in IEQ include micrometers). Use of filters that exceed
ASHRAE’s thermal comfort zone vary the following: minimum requirements is an option
with temperature from approximately • A 10% to 30% reduction in acute to improve IAQ, often with a small or
60% RH at 26°C to 80% RH at 20°C. respiratory infections and allergy and negligible incremental cost.
asthma symptoms.
Sick Building Syndrome • A 20% to 50% reduction in acute non- Maintenance of the HVAC System
The most common health symptoms specific health symptoms (commonly Regular preventative maintenance
attributed by building occupants to their referred to as Sick Building Syndrome) of the HVAC system is necessary to
indoor environments are non-specific • A 0.5% to 5% increase in the assure proper delivery of outside air
health symptoms that do not indicate a performance of office work. throughout the building and to limit
specific disease, such as irritation of eyes, • Associated annual cost savings and growth of microorganisms in the system.
nose, and skin, headache, fatigue, chest productivity gains of $30 billion to Elements of periodic maintenance that
tightness, and difficulty breathing. These $170 billion. are important for maintaining good IEQ
symptoms are commonly called sick include changing of filters, cleaning of
building syndrome symptoms. In some Tips to Ensure Good IEQ drain pans and cooling coils, checks of
buildings, the symptoms coincide with While Designing and Com- fan operation, and checks of operation of
periods of occupancy in the building. missioning HVAC systems dampers that influence air flow rates.
Buildings within which occupants
experience unusually high levels of these Assure Quality of Intake Air Integrated Approach to IEQ
symptoms are sometimes called “sick” Assuring adequate quality of intake air The IEQ performance of a building
buildings. On average, occupants of sealed is essential. Outside air intakes should also depends on the interactions among
air-conditioned buildings report more not be located near strong sources of building design, building materials,
symptoms than occupants of naturally pollutants such as combustion stacks, and building operation, control, and
ventilated buildings. Most studies have sanitary vents, busy streets, loading docks, maintenance. Therefore, an integrated or
found that lower indoor air temperatures parking garages, standing water, cooling whole building approach is recommended
are associated with fewer non-specific towers, and vegetation. The outside air to maximize IEQ. Such an integrated
health symptoms. Symptoms have been intake must be separated sufficiently approach may focus on the following:
reduced through practical measures from locations where ventilation air • IEQ targets or objectives;
such as increased ventilation, decreased is exhausted to prevent significant re- • Occupancy and indoor pollutant
temperature, and improved cleaning of entrainment of the exhaust air. Incoming sources and pollutant sinks and their
floors and chairs (Mendell 1993). air should be filtered to remove particles. variation over time;
The recommended minimum particle • Building and HVAC design.
The lack of a direct relationship between impact of an HVAC system. In the absence a. E Source (1997): E Source Technol-
the Global Warming Potential (GWP) of perfect or ideal refrigerant we should ogy Atlas Series- Volume II: Cooling,
and the Ozone Depletion Potential (ODP) follow a ‘trade-off ’ approach to identify a Boulder, CO, USA.
creates a challenge in developing a rating better combination of HVAC equipment
system that allows the two environmental and its refrigerants to facilitate optimum b. Energy Conservation Building Code,
factors to be considered together, as they environmental impact in terms of GWP Ministry of Power, Indian, May 2007.
should be in evaluating the environmental and ODP per unit of cooling capacity.
c. Fanger, P. O. (1970): Thermal comfort
Refrigerant ODP GWP Application analysis and applications in environ-
CFC-11 1 4600 Centrifugal chillers mental engineering. McGraw-Hill,
CFC-12 0.82 10600 Freezers, chillers, air conditioners New York.
HFC-410A 0 2000 Air conditioning
HCF-134a 0 1600 CFC-12 replacement d. Federspiel, C.C. (1998) “Statistical
analysis of unsolicited thermal sensa-
HCFC-123 0.012 120 CFC-11 replacement
tion complaints in commercial build-
ings”, ASHRAE Transactions 104(1):
power requirements, move less air, avoid • Use of thermal energy storage systems in 912-923
redundancy, and expel their fan heat places where cooling plays a major role in
from the building. peak electricity demand and off peak grid e. Fisk, W.J. and Rosenfeld, A.H. (1997)
energy rate is considerably lower than the “Estimates of improved productivity
Duct layout peak time rate. and health from better indoor envi-
• HVAC duct layout must have a good • Have demand control ventilation for high ronments”, Indoor Air 7(3): 158-172.
design that is planned early in the occupancy spaces. Use of CO2 sensors in
construction process and understood spaces that have varying people density f. Mendell, M.J. (1993) “Non-specific
by the designer and HVAC contractor. loads. health symptoms in office workers:
Every joint and bend in the duct system • Plug leakages in ducts and plenums by a review and summary of the epide-
affects the efficiency of the system. sealing of all the joints. Ensure good miologic literature”, Indoor Air 3(4):
• The duct system must be properly duct work quality, workmanship, duct 227-236.
installed with the correct amount of sealing, functionality of dampers, duct
airflow. cleanliness and testing. g. Nolfo, A.P. (2001): A Primer on
• The duct system must be air sealed, • Use of building management system Testing, Adjusting and Balancing,
insulated and appropriately sized. (BMS) to improve energy efficiency. ASHRAE Journal, May 2001.
Helps in optimizing the run time of
Operation and maintenance equipment at desired levels of efficiency to h. US Department of Energy (2008):
• Maintain high DT chilled water systems maintain building inside temp, humidity, Building Technologies Program Web
with DT up to 9° C to increase the air quality etc within set limits. Site (http://www.eere.energy.gov/
overall energy efficiency of chilled water • Reduce face velocities at coils to increase buildings/).
production and distribution. heat transfer efficiency and reduce
• Incorporate variable speed drives for condensate entrainment i. USGBC (2004): The Treatment by
pumps and fans to efficiently meet partial • Deploy indoor air quality monitoring LEED of the Environmental Impact
load requirements. and Controls system to monitor CO2 of HVAC Refrigerants, LEED TSAC
• Use heat recovery for spaces served by and volatile organic compound levels. Task Force, Washington, DC (http://
AHUs with high OA component. www.usgbc.org/docs/)