DISTRIBUTION OF SYSTEMS USAGE
According to surveys conducted in 1995 by the Department of Energy/Energy Information
Administration (DOE/EIA) of the United States, for a total floor space of 58,772 million ft2 (5462
million m2
) in commercial buildings in 1995 and for a total of 96.6 million homes in 1993 (among
these, 74.1 million homes were air conditioned), the floor space, in million square feet, and the
number of homes using various types of air conditioning systems are as follows:
Much of the floor space may be included in more than one air conditioning system. Given the
possibility that the floor space may be counted repeatedly, the original data listed in the DOE/EIA
publication were modified. The 8 percent of the space system includes part in central hydronic systems
and part in unitary packaged systems. Among the air conditioned homes in 1993, the unitary
packaged system is the predominate air conditioning system in U.S. homes.
HISTORICAL DEVELOPMENT
The historical development of air conditioning can be summarized briefly.
Central Air Conditioning Systems
As part of a heating system using fans and coils, the first rudimentary ice system in the United
States, designed by McKin, Mead, and White, was installed in New York City’s Madison Square
Garden in 1880. The system delivered air at openings under the seats. In the 1890s, a leading consulting
engineer in New York City, Alfred R. Wolf, used ice at the outside air intake of the heating
and ventilating system in Carnegie Hall. Another central ice system in the 1890s was installed in
the Auditorium Hotel in Chicago by Buffalo Forge Company of Buffalo, New York. Early central
heating and ventilating systems used steam-engine-driven fans. The mixture of outdoor air and return
air was discharged into a chamber. In the top part of the chamber, pipe coils heat the mixture
with steam. In the bottom part is a bypass passage with damper to mix conditioned air and bypass
air according to the requirements.
Air conditioning was first systematically developed by Willis H. Carrier, who is recognized as
the father of air conditioning. In 1902, Carrier discovered the relationship between temperature and
humidity and how to control them. In 1904, he developed the air washer, a chamber installed with
several banks of water sprays for air humidification and cleaning. His method of temperature and
humidity regulation, achieved by controlling the dew point of supply air, is still used in many industrial
applications, such as lithographic printing plants and textile mills.
Perhaps the first air-conditioned office was the Larkin Administration Building, designed by
Frank L. Wright and completed in 1906. Ducts handled air that was drawn in and exhausted at roof
level. Wright specified a refrigeration plant which distributed 10°C cooling water to air-cooling
coils in air-handling systems.
The U.S. Capitol was air-conditioned by 1929. Conditioned air was supplied from overhead
diffusers to maintain a temperature of 75°F (23.9°C) and a relative humidity of 40 percent during
summer, and 80°F (26.7°C) and 50 percent during winter. The volume of supply air was controlled
by a pressure regulator to prevent cold drafts in the occupied zone.
Perhaps the first fully air conditioned office building was the Milan Building in San Antonio,
Texas, which was designed by George Willis in 1928. This air conditioning system consisted of one
centralized plant to serve the lower floors and many small units to serve the top office floors.
In 1937, Carrier developed the conduit induction system for multiroom buildings, in which recirculation
of space air is induced through a heating/cooling coil by a high-velocity discharging
airstream. This system supplies only a limited amount of outdoor air for the occupants.
The variable-air-volume (VAV) systems reduce the volume flow rate of supply air at reduced loads
instead of varying the supply air temperature as in constant-volume systems. These systems were introduced
in the early 1950s and gained wide acceptance after the energy crisis of 1973 as a result of
their lower energy consumption in comparison with constant-volume systems. With many variations,
VAV systems are in common use for new high-rise office buildings in the United States today.
Because of the rapid development of space technology after the 1960s, air conditioning systems
for clean rooms were developed into sophisticated arrangements with extremely effective air
filters. Central air conditioning systems always will provide a more precisely controlled, healthy,
and safe indoor environment for high-rise buildings, large commercial complexes, and precisionmanufacturing
areas.
Unitary Packaged Systems
The first room cooler developed by Frigidaire was installed about in 1928 or 1929, and the “Atmospheric
Cabinet” developed by the Carrier Engineering Company was first installed in May 1931.
The first self-contained room air conditioner was developed by General Electric in 1930. It was a
console-type unit with a hermetically sealed motor-compressor (an arrangement in which the motor
and compressor are encased together to reduce the leakage of refrigerant) and water-cooled condenser,
using sulfur dioxide as the refrigerant. Thirty of this type of room air conditioner, were built
and sold in 1931.
Early room air conditioners were rather bulky and heavy. They also required a drainage connection
for the municipal water used for condensing. During the postwar period the air-cooled model
was developed. It used outdoor air to absorb condensing heat, and the size and weight were greatly
reduced. Annual sales of room air conditioners have exceeded 100,000 units since 1950.
Self-contained unitary packages for commercial applications, initially called store coolers, were
introduced by the Airtemp Division of Chrysler Corporation in 1936. The early models had a refrigeration
capacity of 3 to 5 tons and used a water-cooled condenser. Air-cooled unitary packages
gained wide acceptance in the 1950s, and many were split systems incorporating an indoor air handler
and an outdoor condensing unit.
Packaged units have been developed since the 1950s, from indoor to rooftops, from constantvolume
to variable-air-volume, and from few to many functions. Currently, packaged units enjoy
better performance and efficiency with better control of capacity to match the space load. Computerized
direct digital control, one of the important reasons for this improvement, places unitary packaged
systems in a better position to compete with central hydronic systems
Refrigeration Systems
In 1844, Dr. John Gorrie designed the first commercial reciprocating refrigerating machine in the
United States. The hermetically sealed motor-compressor was first developed by General Electric
Company for domestic refrigerators and sold in 1924.
Carrier invented the first open-type gear-driven factory-assembled, packaged centrifugal chiller
in 1922 in which the compressor was manufactured in Germany; and the hermetic centrifugal
chiller, with a hermetically sealed motor-compressor assembly, in 1934. The direct-driven hermetic
centrifugal chiller was introduced in 1938 by The Trane Company. Up to 1937, the capacity of centrifugal
chillers had increased to 700 tons.
During the 1930s, one of the outstanding developments in refrigeration was the discovery by
Midgely and Hene of the nontoxic, nonflammable, fluorinated hydrocarbon refrigerant family
called Freon in 1931. Refrigerant-11 and refrigerant-12, the chlorofluorocarbons (CFCs), became
widely adopted commercial products in reciprocating and centrifugal compressors. Now, new refrigerants
have been developed by chemical manufacturers such as DuPont to replace CFCs, so as
to prevent the depletion of the ozone layer.
The first aqueous-ammonia absorption refrigeration system was invented in 1815 in Europe. In
1940, Servel introduced a unit using water as refrigerant and lithium bromide as the absorbing solution.
The capacities of these units ranged from 15 to 35 tons (52 to 123 kW). Not until 1945 did
Carrier introduce the first large commercial lithium bromide absorption chillers. These units were
developed with 100 to 700 tons (352 to 2460 kW) of capacity, using low-pressure steam as the heat
source.
Positive-displacement screw compressors have been developed in the United States since the
1950s and scroll compressors since the 1970s because of their higher efficiency and smoother rotary
motion than reciprocating compressors. Now, the scroll compressors gradually replace the reciprocating
compressors in small and medium-size refrigeration systems. Another trend is the development of
more energy-efficient centrifugal and absorption chillers for energy conservation. The energy consumption
per ton of refrigeration of a new centrifugal chiller dropped from 0.80 kW/ton (4.4 COPref)
in the late 1970s to 0.50 kW/ton (7.0 COPref) in the 1990s. A series of rotary motion refrigeration compressors with small, medium, to large capacity and using scroll, screw, or centrifugal compressors
will be manufactured from now on.
POTENTIALS AND CHALLENGES
Air conditioning or HVAC&R is an industry of many potentials and challenges, including the
following.
Providing a Healthy and Comfortable Indoor Environment
Nowadays, people in the United States spend most of their time indoors. A healthy and comfortable
indoor environment provided by air conditioning is a necessity for people staying indoors, no matter
how hot or cold and dry or humid the outside climate might be. According to the American
Housing Survey conducted by the U.S. Census Bureau in 1991, of 92.3 million homes, 66 million,
or 71 percent of the total, were air conditioned, and 81.9 million, or nearly 89 percent of the total,
were heated. According to the Energy Information Administration (EIA), in 1992, for a total floor
area of 67.8 billion ft2 (6.3 billion m2
) of commercial buildings, 84 percent were cooled and 91 percent
were heated.
The Cleanest, Quietest, and Most Precise and Humid Processing Environment
Energy Use and Energy Efficiency
Based on the data published in the Annual Energy Review in 1993, the total energy use in 1992 in
the United States was 82.14 quad Btu or 1015 Btu (86.66 EJ, or 1018 J). The United States alone
consumed about one-fourth of the world’s total production. Of the total energy use of 82.14 quad
Btu in the United States, the residential/commercial sector consumed about 36 percent of the total,
the industrial sector consumed another 36 percent, and transportation consumed the rest—28 percent.
Petroleum, natural gas, and coal were the three main sources, providing more than 85 percent
of the energy supply in 1992 in the United States.
According to DOE/EIA energy consumption survey 0321 for residential buildings (1993) and
survey 0318 for commercial buildings (1995), the average annual energy use of HVAC&R systems in the residential/commercial sector was about 45 percent of the total building energy consumption.
Also assuming that the annual energy use of HVAC&R systems was about 1 percent of the total in
both industrial and transportation sectors, then the estimate of annual energy use of the HVAC&R
systems in 1992 in the United States was about 17 percent of the total national energy use, or onesixth
of the total national energy use.
The world energy resources of petroleum, natural gas, and coal are limited. The population of
the United States in 1992 was only about one-twentieth of the world’s total population; however,
we consumed nearly one-fifth of the world’s total energy produced. Energy use must be reduced.
After the energy crisis in 1973, the U.S. Congress enacted the Energy Policy and Conservation
Act of 1975 and the National Energy Policy Act of 1992. The enactment of energy efficiency legislation
by federal and state governments and the establishment of the Department of Energy (DOE)
in 1977 had a definite impact on the implementation of energy efficiency in United States.
In 1975, the American Society of Heating, Refrigerating and Air Conditioning Engineers
(ASHRAE) published Standard 90-75, Energy Conservation in New Building Design. This standard
was revised and cosponsored by the Illuminating Engineering Society of North America as
ASHRAE/IES Standard 90.1-1989, Energy Efficient Design of New Buildings Except New LowRise
Residential Buildings, in 1989; and it was revised again as current ASHRAE/IESNA Standard
90.1-1999, Energy Standard for Buildings Except Low-Rise Residential Buildings, in 1999. Many
other organizations also offered valuable contributions for energy conservation. All these events
started a new era in which energy efficiency has become one of the important goals of HVAC&R
system design and operation.
Because of all these efforts, the increase in net annual energy use for residential and commercial
buildings, i.e., the total energy use minus the electrical system energy loss in the power plant, from
1972 to 1992 in the United States was only 1.3 percent, as shown in Fig. 1.3. However, during the
same period, the increase in floor area of commercial buildings in the United States was about 83
percent. Energy efficiency will be a challenge to everyone in the HVAC&R industry in this generation
as well as in many, many generations to come.
Environmental Problems—CFCs and Global Warming
The surface of the earth is surrounded by a layer of air, called the atmosphere. The lower atmosphere
is called the homosphere, and the upper atmosphere is called the stratosphere.
In the mid-1980s, chlorofluorocarbons (CFCs) were widely used as refrigerants in mechanical
refrigeration systems, to produce thermal insulation foam, and to produce aerosol propellants for
many household consumer products. CFC-11 (CCl3F) and CFC-12 (CCl2F2) are commonly used
CFCs. They are very stable. Halons are also halogenated hydrocarbons. If CFCs and halons leak or
are discharged from a refrigeration system during operation or repair to the lower atmosphere, they
will migrate to the upper stratosphere and decompose under the action of ultraviolet rays throughout
their decades or centuries of life. The free chlorine atoms will react with oxygen atoms of the
ozone layer in the upper stratosphere and will cause a depletion of this layer. The theory of the depletion
of the ozone layer was proposed in the early and middle-1970s. The ozone layer filters out
harmful ultraviolet rays, which may cause skin cancer and are a serious threat to human beings.
Furthermore, changes in the ozone layer may significantly influence weather patterns. Since 1996,
actions have been taken to ban the production of CFCs and halons, before it is too late.
A cloudless homosphere is mainly transparent to short-wave solar radiation but is quite opaque
to long-wave infrared rays emitted from the surface of the earth. Carbon dioxide (CO2) has the
greatest blocking effect of all; water vapor and synthetic CFCs also play important roles in blocking
the direct escape of infrared energy. The phenomenon of transparency to incoming solar radiation
and blanketing of outgoing infrared rays is called the greenhouse effect. The increase of the
CO2, water vapor, CFCs, and other gases, often called greenhouse gases (GHGs), eventually will
result in a rise in air temperature near the earth’s surface. This is known as the global warming
effect.
Over the past 100 years, global warming has caused an increase of 1°F. For the same period,
there was a 25 percent increase of CO2. During the 1980s, the release of CO2 to the atmosphere
was responsible for about 50 percent of the increase in global warming that was attributable to
human activity, and the release of CFCs had a 20 percent share. Some scientists have predicted an
accelerated global warming in the coming 50 years because of the increase in the world’s annual
energy use. Further increases in global temperatures may lead to lower rainfalls, drop in soil moisture,
more extensive forest fires, more flood, etc.
CFC production in developed countries has been banned since January 1, 1996. Carbon dioxide
is the product of many combustion processes. Alternative refrigerants to replace CFCs must also
have a low global warming potential. Designers and operators of the HVAC&R systems can reduce
the production of CO2 through energy efficiency and the replacement of coal, petroleum, and natural
gas power by hydroelectric, solar, and nuclear energy, etc. More studies and research are
needed to clarify the theory and actual effect of global warming.
Air Conditioning or HVAC&R Industry
The air conditioning or HVAC&R industry in the United States is an expanding and progressing industry.
In 1995, the installed value of nonresidential air conditioning hit $20 billion. According to
American Refrigeration Institute (ARI) and Heating/Piping/Air Conditioning data, from 1985 to
1995, the annual rate of increase of installed value of air conditioning systems is 8.7 percent.
Because of the replacement of the old chillers using CFCs, in 1994, the installed value of retrofit,
remodeling, and replacement accounted for up to two-thirds of all HVAC&R expenditures. This
trend may continue in the beginning of the new century.
Based on data from ARI, in 1995, shipment of packaged units reached a record figure of 5
million products, of which heat pumps comprised a one-fifth share. Centrifugal and screw chiller shipments were 7500 units, absorption chillers 502 units, and reciprocating chillers, at a
significantly smaller capacity, were 14,000 units.
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