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INCREASING ENERGY EFFICIENCY
IN BUILDINGS PROJECT CHINA
LEARNING UNIT 04
ENERGY EFFICIENT HVAC SYSTEMS
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Source Document
DESSAU-SOPRINBuilding Engineering
Prepared by: Marie-Judith Jean-Louis, E.I.T.
Martin Par, P.Eng.
Laurier Nichols, P.Eng.
Dessau-Soprin Inc.1441 Ren-Lvesque Blvd. West, Suite 500
Montreal (Quebec) Canada H3G 1T7Phone: (514) 281-1010
Fax: (514) 875-2666Email: [email protected]
Website : www.dessausoprin.com
June 2002O/Ref.: 680514
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TTAABBLLEEOOFFCCOONNTTEENNTTSS
Page
4
AIR CONDITIONERS....................................................................... 1
4.1
INTRODUCTION .....................................................................................................1
4.2
ROOM AIR CONDITIONERS ..................................................................................... 2
4.2.1
Description ........................................................................................................................................ 2
4.2.2 Operation.......................................................................................................................................... 3
4.3
CENTRAL AIR CONDITIONERS ................................................................................ 6
4.3.1
Description ........................................................................................................................................ 6
4.3.2 Operation.......................................................................................................................................... 8
4.4
EFFICIENCY AND PERFORMANCE ...........................................................................9
4.4.1 Energy Efficiency Regulations................................................................................................................ 9
4.4.2 Sizing ............................................................................................................................................. 11
4.4.3 Dehumidifying .................................................................................................................................. 12
4.5
MAINTENANCE ....................................................................................................12
4.6
AIR CONDITIONERS IN CHINA ...................................................................... 14
4.6.1 Introduction ..................................................................................................................................... 14
4.6.2
Chinese Room Air Conditioners ........................................................................................................... 15
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4 AIR CONDITIONERS
4.1 INTRODUCTION
The American engineer Willis Haviland Carrier (1876-1950) is considered to be the father of air
conditioning. He was the first to develop a safe, low-pressure centrifugal refrigeration machine
using non-toxic and non-flammable refrigerant, capable of controlling the humidity and the
temperature in a room. The formulas he worked out and the equipment he used are the basis of
todays air conditioning units.
The air conditioner is a space cooling and dehumidifying unit. There are two basic types of air
conditioners: the room air conditioner and the central air conditioner, both described in more
detail in the next sections. Each of them has its benefits and limitations.
Room air conditioner: Room air conditioners tend to be less expensive than central air
conditioners. They provide zonal cooling. These types of systems dont take much space in a
house and are easy to install. However, they can only condition a small number of spaces and
have a tendency to be noisy because the compressor is situated within the living space it is in.
The cooling efficiency is lower than a central unit because of the installation of only basic
controls.
Central air conditioner:Unlike room air conditioners, central air conditioning units provide
space cooling for the entire house and generally have a larger cooling capacity. On the other
hand, they are more expensive, cost more to install and cost more to operate.
The present chapter will be discussing the different types of air conditioners, their operation and
application.
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4.2 ROOM AIR CONDITIONERS
Description4.2.1
A room air conditioner (Figure 4.2.1) is a small electrically powered unit in an encased assembly
designed to deliver cool conditioned air into a small area, usually one room. These units do not
require any ductwork. There are three main types of room air conditioners: the window-mounted,
the wall-mounted and the portable room air conditioners.
Cooled Room Air
Filter
Warm Room Air
Evaporator
Compressor
Flow Restriction
Fan Motor
Blower
CondenserDischarge Air
Condenser
Outside Air
Figure 4.2.1 Typical Room Air ConditionerSource: Office of Energy Efficiency
Window-mounted: Window-mounted air conditioners can be installed in single and doublehung windows, horizontal sliding and casement windows. These systems are one of themost economical to use when only one room requires cooling.
Wall-mounted:Wall-mounted units are essentially the same as the window-mounted units.
They are also one of the most economical units to use to cool only one room.
FreeStanding Portable: Freestanding portable units are provided with casters, which makethem easy to move from room to room. These units are very economical and practical ifdifferent rooms need to be cooled alternatively, according to the needs of the occupants. In
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this case, moisture from the air is either collected in a built-in tray or sent outdoors throughtemporary coupling sleeves.
Operation4.2.2
Just like a refrigerator or a heat pump in cooling mode, the room air conditioner works by
extracting heat from the space to be cooled and transferring it outside that space. It is important
to note that no fresh air enters the house. The heat transfer is done through the refrigerant lines
but no air is exchanged between the indoor and the exterior. The indoor air is simply cooled,
dehumidified, filtered and returned back in the room. The main components of the room air
conditioner are the condenser, the evaporator, the compressor, the fan, and the refrigerant lines.
The cooling cycle (Figure 4.2.2) operates the same way as the cooling cycle of an air-source
heat pump does, as discussed in the previous chapter. The cooling cycle diagram shows that the
refrigerant goes through four main states (Figure 4.2.3 to 4.2.6) during the cooling process.
Cool dried air Warm moist air
Condenser
Expansion Valve
Evaporator
Air Flow
High-Pressure,High-Temperature Vapour
High-Pressure,High-Temperature Liquid
Low-Pressure,Low-Temperature Liquid
Low-Pressure,Low-Temperature Vapour
CompressorCompressor
Figure 4.2.2 Basic cooling cycleSource: Office of Energy Efficiency
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Low-PressureLow-Temperaturevapor
Low-PressureLow-Temperatureliquid
Figure 4.2.3 Evaporation process
Air Flow
Warm moist air
Low-PressureLow-Temperature Liquid
Low-PressureLow-Temperature Vapour
EVAPORATOR
A fan blows the warm, moist room air to be conditionedthrough the evaporator containing the circulating refrigerant.
As the warm air passes the evaporator, the low-pressure and
low-temperature liquid refrigerant absorbs the heat from the
air and evaporates to become a low-pressure, low-
temperature vapour. During the evaporation process of the
refrigerant, the tube and the fins of the evaporator cools
down, and the moisture from the air condense on the outer
surface of the evaporator. The air that passes through the
evaporation is cooled and its humidity is removed.
COMPRESSOR
High-PressureHigh-Temperature
Vapour
Low-PressureLow-TemperatureVapour
Figure 4.2.4 Compressing process
The cooled air is returned to the room while the low-pressure
and low-temperature vapour refrigerant is sent to the
compressor, which will raise the pressure and the
temperature of the refrigerant by compressing it. The
refrigerant is then a highly pressurized vapour at high
temperature.
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Once the temperature and the pressure of the refrigerant have
been raised by the compressor, it passes through the condenser.
A second fan blows outdoor air onto the condenser in order for
the heat from the refrigerant to be released into the outside air. In
an ideal case scenario, the refrigerant returns to a liquid state
with high temperature and high pressure. However, most of the
time, the refrigerant will return to a mix of liquid and gas at high
pressure and high temperature.
High-PressureHigh-Temperatureliquid
High-PressureHigh-Temperaturevapour
Cool dried air
High-Pressure
High-Temperatureapour
High-PressureHigh-Temperature
Liquid
Figure 4.2.5 Condensation
process
CONDENSER
The high temperature refrigerant at high pressure goes through
the expansion valve where it loses its pressure. Its temperature
is lowered because of the evaporation of refrigerant at this low
pressure. The refrigerant returns to its initial low-pressure and
low-temperature liquid state and the cycle can then be
repeated.
High-PressureHigh-Temperatureliquid
Low-PressureLow-Temperatureliquid
Figure 4.2.6 Expansion process
Low-PressureLow-Temperature
Liquid
High-PressureHigh-TemperatureLiquid
EXPANSION VALVE
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4.3 CENTRAL AIR CONDITIONERS
Description4.3.1
The central air conditioner is designed to cool an entire house through a system of supply and
return ducts. It is composed of an outdoor unit and an indoor unit. A large compressor and a coil
unit are located outdoors and connected by refrigerant lines to the indoor unit composed of a coil
unit and a fan. In some cases, the indoor coil can be mounted in a furnace, as shown in Figure
4.3.1, and the same duct system can be used to heat or cool the house.
ExpansionDevice
Compressor
Outdoor Coil
apourRefrigerant Line
VapourRefrigerant Line
OilBurner
Warm Air Supply Plenum
FurnaceBlower
Add-OnIndoorCoil
Cool AirReturn
Figure 4.3.1 Typical Central Air Conditioner with furnaceSource: Office of Energy Efficiency
Central air conditioners come in various types: the single-package, the split-system, the mini-split,
the mini-duct, and the water-cooled unit.
Single-Package:In the single-package unit, also called the packaged air conditioner, all the
elements are combined in one unit and the conditioned air circulates in a system of supply
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and return ducts. This type of unit is usually mounted on top of a roof or on a concrete slab
next to the houses foundation and going through a wall. This type of system often includes
an electrical heating coil or a natural gas furnace, which eliminates the need for an additional
heating system.
Split-System:The split-system unit is composed of an indoor unit and an outdoor unit. The
indoor unit is connected to the outdoor unit through refrigerant lines and can be mounted on
a furnace. This system resembles the air-source heat pump.
Mini-Split:The mini-split system contains an outdoor unit and 2 or 3 indoor units. This type
of system resembles the split-system unit but does not require any ductwork. The indoor
section is usually mounted on an interior wall, a ceiling or a floor. This type of system is ideal
for houses with new additions. Its lower efficiency has to be taken into consideration.
Mini-Duct:The mini-duct unit also has an indoor and an outdoor component. The indoor
component is generally installed in the attic. Plastic pipes installed in partition walls distribute
both the conditioned air and return air through inlets and outlets. This type of system is ideal
for retrofitted houses where electric or hydronic baseboards are already installed.
Water-Cooled: The water-cooled unit is a system that can be connected to water well or
city water where it is permitted. This type of system is usually not permitted or is used with
restriction in Canada.
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Operation4.3.2
Typical central air conditioners work like room air conditioners, as explained previously. Through
the circulation of the refrigerant, heat is transferred from the space to be conditioned to the
exterior, as shown in Figure 4.3.2.
Cool Indoor AirFan
Inside Coil
Low-Pressure
Low-Temperature Vapour
High-PressureHigh-Temperature Vapour
Outdoor Coil
Compressor
Expansion Device
RefrigerantRelease Heat toOutside Air and
Returns to aLiquid State
Refrigerant AbsorbsHeat from Air andBoils to a VapourState
Low-PressureLow-Temperature Liquid
High-PressureHigh-Temperature Liquid
Figure 4.3.2 Compressor Cycle of a Central Air Conditioner
Source: Office of Energy Efficiency
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4.4 EFFICIENCY AND PERFORMANCE
Air conditioners in Canada have an energy efficiency-rating label that gives information to
consumers on how many Btu per hours of heat is removed for each watt of power supplied to the
unit. For room air conditioners, the energy efficiency rating is the Energy Efficiency Ratio (EER),
while for the central air conditioner the energy efficiency rating is Seasonal Energy Efficiency
Ration (SEER).
Room Air Conditioner:Most room air conditioners range from 5,500 Btu to 14,000 Btu. In
North America, the EER of window-mounted air conditioners can vary between 8.0 and 12.0,
while the EER of wall-mounted air conditioners usually ranges between 8.0 and 8.5. Highly
efficient room air conditioners will generally have efficient rotary compressors, largeevaporators and condensers, efficient fans and slinger rings to deposit water collected from
the evaporator onto the hot condenser.
Central Air Conditioner:The split-type central air conditioner is required to have a minimum
SEER of 9.7, while package-type central air conditioners are required to have a minimum
SEER of 10.0. Currently, some central air conditioners reach a SEER of 17.0. Energy
efficient central air conditioners differentiate themselves from conventional systems by using
components such as more efficient compressors, larger and more effective heat exchanger
surfaces and better refrigerant flow.
Energy Efficiency Regulations4.4.1
In Canada, the room air conditioner and the central air conditioner are both covered by the
federal Energy Efficiency Regulations. Air conditioners are required to meet minimum energy
efficiency standards of performance in order to be either imported in Canada or shipped abroad.
Room Air Conditioner:Room air conditioners are required to carry an EnerGuide label. The
purpose of this label is to accurately inform customers about the relative energy efficiency of
these units. The EnerGuide contains information about the energy efficiency ratio (EER) of
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the room air conditioner, a scale that compares its EER with other models from the same
class of air conditioner, and the type of unit. Room air conditioners are grouped into louvred
or non-louvred units and classified according to the category of cooling capacity they belong
too.
Figure 4.4.1 is an example of an EnerGuide label showing: (A) the energy efficiency ratio of
the room air conditioner, (B) the energy efficiency ratio of the least energy efficient model and
(C) the energy efficiency of the most energy efficient model compared to others that fall
within the same class as the model tested, (D) the energy efficiency ratio indicator, and (E)
the type and the cooling capacity range of the model tested and similar models compared.
Figure 4.4.1 EnerGuide label (EER)Source: Office of Energy Efficiency
Central Air Conditioner:Central air conditioners are also required to carry an EnerGuide
label. However, the seasonal energy efficiency ratio (SEER) is used in the regulations for
this type of system. As for the EnerGuide for the room air conditioner, the one for the
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central air conditioner contains information about the SEER of the model being tested, and
its comparison with other models (Figure 4.4.2).
Figure 4.4.2 EnerGuide label (SEER)Source: Office of Energy Efficiency
Sizing4.4.2
The capacity of an air conditioner depends on the size of the house or rooms to be conditioned,
window exposure, size and orientation, the material used in the construction of the house, the
level of insulation, air infiltration, internal heat gains and the lifestyle of the inhabitants. It is
important not to oversize an air conditioner because although it will cool the air faster, it will not
run long enough to properly dehumidify the space to a comfortable level, as explained in the
previous chapter.
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Dehumidifying4.4.3
The dehumidifying process requires a substantial amount of energy, which reduces the efficiency
of an air conditioner. Many manufactures reduce condensation by keeping the condenser
somewhat warmer to help improve the efficiency of the unit. As a result, some of the new high-
efficiency air conditioners do not dehumidify as effectively as other systems. Some air conditioner
models have a humidistat that controls the speed of the fan in order to help reduce the humidity.
4.5 MAINTENANCE
Regular maintenance of an air conditioner ensures its longevity and its efficiency. Failure to
properly maintain the unit will reduce its efficiency while increasing its operational cost. The
following is a list of maintenance procedures necessary to protect the efficiency of an air
conditioner.
Unit Location:When possible, the outside compressor unit should be located in the north
side of a house or where there is the most amount of shade, when possible, to reduce the
work provided by the unit and increase its efficiency.
Outside Compressor: The outside compressor should always be kept clean and free of
grass, twigs or leaves as they could cause the compressor to overheat and therefore
seriously damage the unit.
Window Units: If a window unit is left in place in the winter, the portion inside should be
wrapped and weather-stripping should be added around the unit to block the infiltration of
cold air into the house. It is important not to wrap the portion of the unit located outdoors
because the warm, moist air from inside the room could infiltrate the unit. If this were to
happen, the water contained in that air would freeze and cause serious damage to the unit.
Filters:The filters of an air conditioner should be replaced and cleaned regularly. Failure to
do so will result in a significant reduction of the efficiency of the system. Dirty or clogged
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filters will reduce the airflow and the dirt will most probably be carried directly to the
evaporator coil, and alter its heat absorbing capacity.
Coils:The evaporator and the condenser coils will inevitably collect dirt over their years of
service. The dirt will act as an insulation film and reduce the transfer of heat between the
coils and their environment. It is therefore important to check and clean the coils regularly.
The fins of the coils are also easily bent. They should be straighten back to their original
position in order for the airflow not to be blocked, which would reduce the efficiency of the air
conditioning system.
Ducts: 10% to 30% of the air from conventional systems is lost through duct leakages. In
order to limit duct leakage, a professional using the necessary test equipment should inspect
the duct. They should be sealed with mastic and should be airtight in order for the system to
be efficient.
Temperature differences between the ducts and the duct space causes heat transfers. For
this reason, it is important to insulate air ducts to save energy. In many cases however, the
cost of insulation will be greater than the potential energy savings of insulating the ducts. This
is why, in the majority of homes using ducts to circulate cooled air, the ducts will not beinsulated.
Obstruction:Obstruction can be as unfavorable as air leakage and reduce the efficiency of
an air conditioner. It is important not to block the flow of the air supply or the air return with
objects like furniture or drapes.
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4.6 AIR CONDITIONERS IN CHINA1
4.6.1 Introduction
The Shanghai Refrigerator Factory was the first to produce a Chinese air conditioner in 1963. Atthat time, air conditioners were not very popular because the consumption standard at the time
was low and power companies imposed very strict policies with regard to the use of electricity.
The production of air conditioners in China started slowly but has accelerated rapidly since the
mid-80 due to the increase in Chinese living standards and the changing attitudes towards
energy consumption.
In 1989, the State Bureau of Quality and Technical supervision approved the National Standard
GB12021.3 Room Air Conditioner Energy Consumption Limits and Testing Method established
by the National Technical Committee for Energy Basis and Standardization of Management. One
year later, this standard went into effect as the second of the first 8 standards developed for
household appliances. The implementation of this standard created a stimulus to increase the
production of more energy efficient air conditioners and to purchase models of a higher quality.
As a result, the production of Chinese air conditioners started to increase from 1990 onwards
(Figure 4.6.1).
1The information in the following section comes primarily from a report entitled Technical and Economic Analysis of
Energy Efficiency of Chinese Room Air Conditioners (Fridley et al., 2001). An analysis of Chinese room airconditioners was conducted in order to evaluate the Chinese National Standard GB12021.3 (1989) and proposechanges. The purpose of this section is to give some basic information on the background and status of airconditioners in China. For more information, please refer to the above-mentioned report.
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Currently, air conditioners are one of the top three household electricity consumers, along with
lighting and refrigerators. During the summer months, air conditioners are the largest consumers
of domestic electricity. The Chinese market is increasing at a very rapid pace. According to a
China Statistical Bureau evaluation, in the three years between 1995 and 1998, the production of
air conditioners increased by 125%. The demand and production of air conditioners in China is
expected to continue to grow in the years to come.
Figure 4.6.1: Air Conditioner Production, 1980-1998Source: Fridley et al., 2001
Chinese Room Air Conditioners4.6.2
In the GB1202.3 (1989), air conditioners were classified in six groups according to the
configuration of the unit and its cooling capacity, as shown in the following table (Table 4.6.1).
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Table 4.6.1 Types of room air conditioners from GB12021.3
Configuration of the unit Cooling Capacity (thermal watts)
Split Below 2500 W Window-type Between 2500 W and 4000 W
Above 4500 WSince air conditioners were changing, China issued another standard called the GB/T7725
Room Air Conditioners in 1996. This standard classifies air conditioners into 14 types according
to their cooling capacity under different climate conditions, their structure and their function as
shown in the following table (Table 4.6.2).
Table 4.6.2 Types of room air conditioners from GB/T47725
Maximum Cooling Capacity Type of Structure Type of function
Class T1 Single packages Cooling only Class T2 Split Heat pump Class T3 Cooling with electrical components
After studying Chinese air conditioners, Fridley et al. proposed the following design options that
would increase the efficiency of the air conditioners.
Increase the heat transfer surface area by improving the performance of the coil Improve heat transfer rate Increase the efficiency of the compressor Increase the efficiency of the fan and fan-motor
Integrate control systems Integrate a flow control device Use alternative refrigerant
According to their analysis, if an EER standard2of 2.92 W/W had come into effect in 2001, over
3.5 billion Yuan would be saved between 2001 and 2020, while carbon emissions would be
reduced by 12 million metric tons. Consequently, increasing the efficiency of air conditioners will
have a significant impact on energy costs and the polluting levels of residential households in
China.
2 An EER of 2.92 W/W in China corresponds to an EER of 9.97 Btu/h / W in North America.
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REFERENCES
ASHRAE, 1996 HVAC System and Equipment Handbook, American Society of Heating, Refrigeratingand Air-Conditioning Engineers Inc., Inch-Pound Edition, Atlanta, United States, 1996FRIDLEY, David; ROSENQUIST, Gregory; LIN, Jiang; AIXIAN, Li; DINGGUO, Xin & JIANHONG,
Cheng; Technical and Economic Analysis of Energy Efficiency of Chinese Room Air Conditioners;[1] Energy Analysis Department, Environmental Energy Technologies Division, Lawrence Berkeley NationalLaboratory, University of California, USA; [2] China National Institute of Standardization (CNIS), Beijing,China; [3] Beijing Energy Efficiency Center (BECon), Beijing, China; LBNL-45550; February 2001, 56pagesENERGY EFFICIENCY AND RENEWABLE ENERGY NETWORK (EREN), Energy-Efficient AirConditioning, Consumer Energy Information: EREC Fact Sheets, U.S. Department of Energy, DOE/GO-10099-379, FS 206, last update: June 1999, http://www.eren.doe.gov/erec/factsheets/aircond.htmlMISSOURI DEPARTMENT OF NATURAL RESOURCES, Residential Energy Efficiency AirConditioning, Energy Center, Residential Energy Efficiency,last update: September 08 2000,http://www.dnr.state.mo.us/de/residential/airconditioning.htm
MASSACHUSETTS INSTITUTE OF TECHNOLOGY, William Haviland Carrier, The Lemelson MITAwards Program, Invention Dimension, Inventor of the Week Archives, last update: June 2001,http://web.mit.edu/invent/www/inventorsA-H/carrier.htmlNAGYSZALANCZY, Sandor, Getting Your Air Conditioner Ready for Summer, Corner Hardware,http://www.cornerhardware.com/html/articles/art50.htmOFFICE OF ENERGY EFFICIENCY (OEE), Air Conditioning Your Home, Natural Resources Canada,Cat. No. M91-23/7, ISBN 0-662-26590-4, 1998, http://energy-publications.nrcan.gc.ca/pub/home/Air_Conditioning_Your_Home.cfm
http://www.eren.doe.gov/erec/factsheets/aircond.htmlhttp://www.dnr.state.mo.us/de/residential/airconditioning.htmhttp://www.dnr.state.mo.us/de/residential/airconditioning.htmhttp://www.dnr.state.mo.us/de/residential/airconditioning.htmhttp://web.mit.edu/invent/www/inventorsA-H/carrier.htmlhttp://www.cornerhardware.com/html/articles/art50.htmhttp://energy-publications.nrcan.gc.ca/pub/home/Air_Conditioning_Your_Home.cfmhttp://energy-publications.nrcan.gc.ca/pub/home/Air_Conditioning_Your_Home.cfmhttp://energy-publications.nrcan.gc.ca/pub/home/Air_Conditioning_Your_Home.cfmhttp://energy-publications.nrcan.gc.ca/pub/home/Air_Conditioning_Your_Home.cfmhttp://energy-publications.nrcan.gc.ca/pub/home/Air_Conditioning_Your_Home.cfmhttp://www.cornerhardware.com/html/articles/art50.htmhttp://web.mit.edu/invent/www/inventorsA-H/carrier.htmlhttp://www.dnr.state.mo.us/de/residential/airconditioning.htmhttp://www.eren.doe.gov/erec/factsheets/aircond.html