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— By Rita Tatum, Contributing Editor
(Editor\'s Note)
“If we do it right, protecting the climate will yield not costs, but profits: not burdens,
but benefits; not sacrifice, but a higher standard of living,” said President Bill Clinton
last October when he announced the position that he would take in negotiations for the Kyoto
Protocol. “There is a huge body of business evidence now showing that energy savings give
better service at lower cost with higher profit.” In the second part of a special series,
Building Operating Management examines HVAC technologies that offer significant energy-saving
potential. Part 1 examines lighting technologies; Part 3 looks at the building envelope.
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Under the Kyoto Protocol, the United States will need to cut its energy use while the number
of energy users continues to grow. This is not the first time the United States has tackled
an energy problem and won with practical applications of energy-saving technology. Between
1979 and 1986, the nation’s economy soared 19 percent. Yet thanks to Yankee ingenuity total
energy use dropped 6 percent.
True, that movement was motivated by the threat of high energy prices. But high prices are
not the only reason Americans choose to conserve. In Seattle, which has the cheapest
electricity of any major U.S. city, residents saved electric loads nearly 12 times as fast as
those in Chicago between 1990 and 1996, even though Seattle pays about half the price per
kilowatt-hour as Chicago does. They saved it because Seattle City Lights, a city-owned
electric utility, showed them how. The moral of the story, according to the Rocky Mountain
Institute, is that “an informed, effective and efficient market in energy-saving devices and
practices can fully substitute for a bare price signal, and indeed can influence energy-
saving choices even more than price can alone.”
Chiller Improvements
HVAC technology is the perfect example of the profitability of energy efficiency. Consider
chillers. New units can be 40 percent more efficient than ones installed 20 years ago.
Replacement of older chillers will also free facility executives from dependence on CFCs. The
Environmental Protection Agency has calculated that when 44 percent of CFC chillers are
replaced or converted, chiller owners will reduce energy use by 7 billion kilowatt-hours per
year, saving $480 million annually.
Savings can be even greater when buildings are upgraded to reduce the cooling load before
chillers are replaced, allowing smaller chillers to be installed. A pilot project by Pacific
Gas and Electric Company’s Advanced Customer Technology Test featured a 20,000-square-foot
office building retrofit in San Ramon, Calif. Improved glazing, more efficient lighting and
better controlled HVAC systems allowed chiller capacity to be reduced more than 40 percent
because of better solar control from the windows and the reduced internal loads from the
lighting. The savings from the smaller chiller offset some of the cost of the window and
lighting retrofits.
Heat-Recovery Technologies
In commercial facilities that require both heating and cooling, heat-recovery chillers offer
low-cost thermal energy. A heat-recovery chiller uses its condenser to collect heat that
would otherwise be wasted and then applies it to water heating, space heating, reheating or
process heating. Heat-recovery chillers have been used for more than 30 years. They are
available as a standard option from almost all manufacturers. Still, they account for just 2
to 5 percent of total chiller sales, possibly because they are slightly more expensive and
require a bit more energy to produce cooling.
However, the useful heat output can quickly return the investment and provide continuing
operating cost savings, as the Carter Presidential Center in Atlanta has discovered. The
150,000-square-foot facility includes a museum, library, offices and conference center with a
restaurant. One 200-ton centrifugal heat-recovery chiller and one 200-ton cooling-only
chiller meet the complex’s 400-ton peak cooling load. Heat is supplied by the heat-recovery
chiller or a boiler. Because strict control of temperature and humidity is required in
document storage areas, reheat is a necessity.
The heat-recovery chiller operates as the lead chiller during the heating season, supplying
chilled water to meet the cooling load and hot water for space heating and terminal reheat.
In summer, when cooling is the greater concern, the heat-recovery chiller operates when
cooling loads rise above the capacity of the cooling-only chiller and when the humidity
increases.
According to the General Services Administration, the center’s HVAC energy consumption is 35
percent lower than for a similar, conventionally designed facility.
Heat-recovery chillers are conventional chillers with double-bundle condensers or
desuperheaters. Heat-recovery heat pumps, on the other hand, are separate refrigeration
machines that recover heat from a waste heat source — in commercial buildings, typically a
conventional chiller system. Heat-recovery chillers are normally controlled by a cooling
load, while heat-recovery heat pumps are controlled by the heating load. Heat-recovery heat
pumps are capable of delivering hot water at higher temperatures, 120 F and up, while heat-
recovery chillers are usually limited to 120 F or less.
Geoexchange Systems
Geothermal heat pumps have been cooling homes for years. In the past decade, they have been
making inroads into commercial and school buildings as well. The Energy Information
Administration says more than 155,000 geoexchange systems were installed between 1994 and
1996, most of them small systems averaging 3.4 tons. Once called earth-coupled heat pumps,
they are now referred to as geoexchange systems, but the principle of operation has not
changed: use the earth’s stable ground temperature to help in space conditioning.
Geoexchange systems circulate water or other liquids through underground pipes. In cold
weather, the system transfers the earth’s heat through the pipes into the circulating liquid,
which transfers it into the building. In hot weather, the fluid in the system’s pipes takes
warmth from the building and transfers it into the cooler earth.
“Geothermal technology is very versatile,” says Mukesh Khattar, Electric Power Research
Institute (EPRI) team leader of refrigeration, HVAC and thermal storage technologies.
“Today, there are many documented geoexchange systems in commercial applications,” says
Steve Rosenstock, manager of technology policy at Edison Electric Institute. “Many schools,
college campuses and different commercial buildings around the country are using it.” One
difficulty: Geoexchange systems need land in which to bury the piping and, in urban areas,
such land may be at a premium.
A McDonald’s restaurant near Detroit is one of the first in the chain to use the earth for
its heating and cooling needs. The restaurant’s geoexchange system, installed with the help
of Detroit Edison and EPRI, will provide energy at reduced cost.
Dave Daniels, director of operations for Detroit Region McDonald’s, says they will monitor
and evaluate the 3,600-square-foot restaurant’s energy use and examine the potential of
geoexhange technology for savings at future locations.
Gas-Fired Systems
Air conditioning involves both temperature reduction and dehumidification. Conventional
equipment handles both, but can be less effective when the dehumidification load is greater
than the temperature cooling load. Gas-fired desiccant cooling systems are more effective in
reducing humidity and are particularly attractive for buildings affected by high humidity.
Consider locations with indoor swimming pools. The American Hotel and Motel Association
estimates that humidity-related damage costs its members almost $70 million annually in
repairs and lost revenues.
Desiccant systems do not use refrigerants, compressors or absorption cycles. Instead,
desiccant materials attract and retain moisture from the air. Air from a building is dried as
it flows through the desiccant and then cooled, when necessary, with a supplemental chiller.
Once it is saturated, the desiccant material is heated to evaporate the moisture and to
prepare it for reuse. Current gas-fired desiccant systems include down-sized electric vapor
compressors to provide temperature cooling. However, more advanced gas systems now being
developed would not require any major electrical components.
Two other natural gas technologies are making inroads into the chiller market: engine-driven
gas chillers and gas absorption cooling. The absorption process uses vaporization or
evaporation to produce a cooling effect. The refrigerant is water.
Gas absorption systems also differ from electric chillers in that the refrigerant is restored
or regenerated by heating rather than mechanical compression.
Natural gas engine-driven chillers package two well-known technologies — vapor-compression
refrigeration and natural gas engines — coupling them with an advanced control system. The
primary difference between these chillers and electric units is that the compressor is driven
by a natural gas engine instead of an electric motor.
Thermal Storage
Using conventional chillers to store energy in chilled water, ice or other materials, thermal
energy storage systems (TES) shift energy consumption from peak afternoon electricity rates
to low nighttime periods. TES systems also offer a positive option for helping meet the Kyoto
Protocol because they cut pollutants at the power plant’s source. Utilities operate their
most efficient plants through the nighttime period. According to a report from the California
Energy Commission, a 20 percent market penetration by TES by 2005 “could save enough energy
to supply over a third of the new air conditioning load projected.” The report was prepared
with the International Thermal Storage Advisory Council and the Air-Conditioning and
Refrigeration Institute.
Many California TES systems shift between 40 and 80 percent of the facility’s annual kilowatt
hours for air conditioning from daytime to nighttime consumption. TES in California could
save 1,300 gigawatt- hours of source energy, enough to supply all 500,000 electric cars
projected to exist in the state in 2005.
Heating Technologies
The heating end of HVAC technology has become so efficient that it now approaches physical or
economic limits, according to a September 1997 Department of Energy (DOE) study. “In many
cases, appliance and equipment efficiencies are reaching either their thermodynamic limits,
or can be made higher only at significantly higher first cost,” says the study.
Condensing boilers and pulse-fired combustion boilers offer very high efficiencies, at and
above the 90 percent combustion efficiency range. In addition, they benefit from stackless
venting. These boilers achieve high efficiencies by heat transfer and recapture, so their
exhaust temperature is low. Manifolded systems of small boilers also can offer high
efficiencies, because each of the boilers operates at its optimum load, cycling off when not
needed.
Natural gas-fired furnaces can also operate in the 90 percent plus efficiency range and are
now offered in compact designs so they can be conveniently installed in existing buildings.
In addition, says the DOE study, “electric resistance water heaters have become more than 90
percent efficient with 100 percent as the maximum. Gas water heaters and refrigerators
provide other examples where efficiencies may be reaching either an economic or thermal
limit. Condensing gas water heaters that have efficiencies above 90 percent have been
developed, but are generally too expensive for a mass market.”
Future Horizons
If conventional HVAC is approaching its thermodynamic limits, where are tomorrow’s
refinements likely to be? The DOE study suggests research efforts need to focus on “multi-
functional equipment and appliances to provide the next quantum jump in efficiency
improvement.” An example of multi-functional equipment might be an integrated water heating
and space conditioning system that uses heat pump technology to meet space heating, air
conditioning and water heating loads. According to DOE scientists, such an integrated HVAC
system could have a seasonal energy efficiency ratio (SEER) that is 70 percent higher than
the combined efficiency of today’s central air conditioning system and water heating system.
In addition, energy-efficient air filtration, as well as humidity and temperature control,
could be incorporated into tomorrow’s HVAC systems to reduce indoor concentrations of
airborne particles. “Further opportunities exist for improving the efficiency of heating and
cooling systems in buildings through integrated systems design, right sizing,
modular/multiple equipment configurations and better integration of the process for
distributing space heating and cooling within buildings,” according to DOE.
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