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Space heating and cooling use 46% of all energy consumed in U.S.
residential buildings. Water heating accounts for an additional
14%. Total energy consumption for space conditioning in commercial
buildings is 4.5 quads, and commercial refrigeration accounts for
0.6 quads. In some commercial buildings like supermarkets, the percentage
of energy consumed for refrigeration commonly approaches 50%.
More than half of the total energy used for heating, cooling, ventilation,
refrigeration, and water heating is electrical, and air conditioning
is the single leading cause of peak demand for electricity. Reducing
these loads can lower demand for annual power generation and peak
capacity. Furthermore, to realize the future promise of net-zero
energy buildings—buildings using on-site power generation to
produce much of their required energy—thermal and electrical
loads must be minimized.
Advanced technologies already have demonstrated success in increasing
the energy efficiency of these vital building functions, without
compromising occupant comfort or equipment performance. Yet the
opportunity for further energy efficiency improvements remains large.
Targets include chiller systems used in cooling large commercial
buildings, small unitary heating and cooling equipment used in residential
buildings, unitary rooftop packages used in light commercial buildings,
and commercial refrigeration systems used in supermarkets. For example,
DOE and partners are working on energy efficiency improvements to
glass-door supermarket display refrigeration cabinets. These improvements,
along with other energy-saving changes, have the potential to reduce
the energy consumption of commercial refrigeration in supermarkets
by 60%.
Benefits of advanced technology do not stop with energy and cost
savings, but extend to environmental protection and health. For
example, new technologies are minimizing environmental impacts related
to refrigerants, and more effective ventilation and space conditioning
are demonstrating the potential to enhance the health and productivity
of building occupants by improving air quality.
Program Goals
By conducting R&D in cooperation with industry partners, DOE
seeks to accelerate the development and introduction of highly efficient
heating, ventilating, refrigeration, and air-conditioning systems,
and water-heating technologies.
Component-level research has centered on heat pumps and refrigeration
technologies, with a focus on dramatically improving the energy
efficiency of residential and commercial heat pump and refrigerating
equipment; applying advances in refrigeration research to nontraditional
applications such as water heating and integrated appliances; providing
industry with data on new refrigerants to replace chlorinated refrigerants
in buildings applications; and working with industry to establish
a knowledge base of safety, performance, and operational characteristics
of new refrigerant/lubricant mixtures. Other DOE R&&D addresses
models, methodologies, controls, communications, and design tools
for better integrating equipment within a whole building, in ways
that optimize energy use and performance.
The target of these efforts is to reduce annual energy use and
peak loads for building equipment by 20% in 2020, versus 2003. DOE
laboratories engaged in this R&&D include the Oak Ridge National
Laboratory, through its Buildings Technology Center, and the Lawrence
Berkeley National Laboratory.
A specific program goal is to develop, by 2010, technology for
affordable small heating, cooling, and water heating components
for use in commercial buildings, in support of the net-zero-energy
building concept. Such components would be sized to match the
capacities of cost-efficient on-site generators, using solar, fuel
cell, or other distributed power technologies.
Strategy
DOE's R&D activities in heating, cooling, and commercial refrigeration
technologies reflect the priorities identified by the industry roadmap
, together with DOE
strategic goals.
The roadmap identifies the key technological challenges in developing
equipment that balances the requirements of environmental sustainability
while responding to the needs of the marketplace for safe, reliable,
effective, and affordable systems. Overarching industry goals include
reducing operation, maintenance, and energy costs; reducing waste
and pollution; increasing equipment durability and flexibility;
increasing occupant productivity, comfort, and health; and reducing
construction worker illnesses and injuries.
DOE, with industry partners, focuses on pre-competitive research
that resolves significant technological hurdles. Individual manufacturers
then apply the research results to provide products that satisfy
market needs.
Current Research
DOE conducts laboratory and field research, design, and testing
of heating and cooling systems, refrigeration systems, components,
and replacement refrigerants. Areas of expertise include high-efficiency
electric and gas heat pumps, refrigerator/freezer modifications
to increase efficiency and eliminate CFC and HCFC refrigerants,
cogeneration and central heating and cooling plants, thermally activated
gas heat pumps, and assessments of global warming impacts of alternative
refrigerants.
DOE also is investigating ways to combine the operation and control
of a building's equipment (for heating, cooling, and water heating)
together with its thermal envelope, thermal delivery, and ventilation
systems in a total system design approach to maximize overall delivered
energy efficiency. Right-sizing of heating, cooling, and ventilation
equipment is a key aspect of optimizing energy efficiency within
a whole building system.
Current R&D activities focus on:
Diagnostic and real-time monitoring tool—Diagnostic
tools improve equipment performance by signaling the need for preventive
maintenance or repairs, and monitoring tools allow real-time control
of energy loads. DOE and its partners are currently developing a
charge indicator—an on-board diagnostic tool that measures
the charge of working fluid on vapor compressors, alerting facility
managers or homeowners of the need for recharging. Heat pumps are
the initial target application. Other potential applications include
commercial refrigerators, heat pump water heaters, small residential
heating and cooling equipment, and large chillers. Other current
developments are the coefficient of performance (COP) meter, an
on-board or hand-held device that assesses heating and cooling equipment
efficiency by measuring charge, air flow, and temperature; and the
distributed package terminal air-conditioner (PTAC) controller,
which allows real-time monitoring and control of package terminal
air-conditioners, enabling commercial facilities to automatically
turn off cooling in unoccupied rooms, or to selectively shed loads
in periods of peak demand.
Design tool for heat pumps and air conditioners—A widely
used tool developed by DOE through Oak Ridge National Laboratory
is the Heat Pump Design Model (Mark VI release). This tool simulates
the steady-state cooling and heating performance of air-to-air heat
pumps and air conditioners, enabling users to specify such key parameters
as type of vapor compressor, type of heat exchanger, air conditions,
air flows, and type of refrigerants. The program can be used with
most of newer HFC refrigerants as well as with HCFCs and CFCs. Versions
are available for single-speed and variable-speed heat pumps. Manufacturers
of heat pump systems and components have used the model extensively
in product design and ratings, and contractors have applied it to
assessing installation designs. The model is periodically upgraded
to increase its usefulness to U.S. industry and researchers for
product design and development. Future versions will simulate geothermal
heat pumps and mini splits (room or zone heat pumps that do not
require ducts).
Improvements in supermarket refrigeration—Current supermarket
refrigeration systems have the potential for significant refrigerant
leak rates and high power consumption. DOE has assessed several
system concepts that feature greatly reduced refrigerant charge
and emission levels, and integration of the stored heating/cooling
equipment to recover the refrigeration reject heat for space heating.
A field demonstration, conducted in collaboration with a supermarket
chain, an electric utility in Massachusetts, and the Electric Power
Research Institute (EPRI), showed that a distributed refrigeration/water-source
heat pump HVAC system could achieve about 20% primary energy savings
in the Massachusetts area compared to a state-of-the-art conventional
refrigeration/HVAC arrangement.
Frostless heat pump—When ambient temperatures fall
below about 40F, frost begins to build up on the outdoor heat exchanger
coil of conventional heat pumps, diminishing their heating effectiveness.
Periodic defrosting is required, during which a four-way valve temporarily
reverses the heat pump cycle, diverting heat from inside the house
to the outdoor coil. To temper the resulting drop in temperature
of the air supplied to the indoor space, conventional systems energize
supplemental resistance-heating elements. However, even with substantial
power flowing through the heating elements, the indoor air temperature
is temporarily lowered—resulting in what is commonly called
"cold blow," a major concern of heat pump manufacturers and consumers.
The defrosting cycle not only reduces occupant thermal comfort and
causes power surges, but also decreases system reliability because
of the stresses imposed on such components as the four-way valve,
the compressor, and the resistance-heating elements.
The frostless heat pump, developed with support from DOE and industry
partners, cost-effectively addresses these concerns by drastically
reducing the frequency of defrost cycling (by a factor of 5 in the
Knoxville, Tennessee area) and by eliminating cold blow. The key
innovation is the addition of heat to the accumulator, which increases
the temperature of the refrigerant entering the outdoor coil. Tests
have shown that the addition of moderate amounts of heat dramatically
retards frost formation over a substantial range of outdoor ambient
conditions where frost is likely to form. When the frostless heat
pump does require cycle reversing, the indoor fan is shut off, thus
avoiding "cold blow" draft and heat removal from the conditioned
space.
Thermally activated heat pumps—Heat pumps in use today
are electrically driven, operating on the conventional vapor-compression
refrigeration cycle. Thermally activated heat pumps that operate
on natural gas fuel have the potential to revolutionize the way
residential and commercial buildings are heated and cooled. Such
natural gas driven heat pumps can achieve substantial improvements
in energy efficiency by avoiding the energy conversion losses (approximately
70%) associated with electric power generation and distribution.
Highly efficient heat pumps could outperform the best natural gas
furnaces, reducing energy use by as much as 50%, while also providing
gas-fired air conditioning. In large commercial-size absorption
chillers, energy efficiency can be improved by 50% with advanced
high-temperature cycles and novel fluids. Working with industry
and utilities, DOE is developing and testing thermally activated
technologies in residential absorption heat pumps, such as the generator
absorber heat exchange (GAX) cycle heat pump and the "Hi-Cool" heat
pump; and in large commercial chillers with double-condenser-coupled
cycles.
Residential thermal distribution systems—Systems to
distribute heating and cooling throughout a house include forced
air systems, radiant floors, hot water radiators, and electric systems
such as baseboard heaters. Because nearly all new homes in the United
States feature forced air distribution, these systems have been
the focus of recent DOE research. Typical duct systems lose 25%
to 40% of the heating energy or cooling energy put out by a central
furnace, heat pump, or air conditioner. Air leaks are one source
of energy losses. Another source is conduction losses, which are
greatest when ducts are installed outside the conditioned (heated
and cooled) parts of the house—as the National Association
of Home Builders found to be the case in 67% of new homes with forced
air distribution built between 1996 and 1998.
Improving thermal efficiency can yield dramatic reductions in energy
costs. DOE research, conducted in conjunction with Habitat for Humanity
and Oak Ridge National Laboratory, measured the energy savings realized
by placing the thermal distribution system inside the conditioned
space—and demonstrated a 30% to 40% savings in both the heating
and cooling energy demand for a 1200-square-foot house. DOE is working
on several new technologies for improving duct efficiency and enabling
easier installation within conditioned space.
Recent work at the Lawrence Berkeley National Laboratory has evaluated
different methods for measuring air leakage from ducts. The American
Society for Testing and Materials will rewrite its standards for
duct leakage testing based on the results of field testing of these
methods. DOE also initiated the development of American Society
of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE)
Standard 152, a testing method to rate the energy efficiency of
residential thermal distribution systems.
Simulation results showed that improved ducts (low leakage) and
improved system installation (moving ducts into conditioned space
form the attic) can allow the use of a smaller nameplate capacity
air conditioner without reducing the cooling effect actually delivered
into the occupied space or the "pulldown" time required to cool
down the house after it has been allowed to heat up all day.
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