Geothermal Heat Pumps
Summary: This section will provide you with an overview on how a geothermal heat pump (GHP) can provide an energy efficient way to heat and cool your home. If you're planning to build a new house, office building, or school, or replace your heating and cooling system, you may want to consider a geothermal heat pump (GHP) system. GHP systems are also known as GeoExchangeSM, ground-source, or water-source heat pumps (as opposed to air-source heat pumps). Regardless of what you call them, energy efficient geothermal heat pumps are available today for both residential and commercial building applications.
A Geothermal Heat Pump system can be installed in virtually any area of the country and will save energy and money. According to the Environmental Protection Agency (EPA), GeoExchange systems are the most energy efficient, environmentally clean, and cost-effective space conditioning systems available (source: "Space Conditioning: The Next Frontier," EPA 430-R-93-004, April 1993).
While residential Geothermal Heat Pump systems are usually more expensive initially to install than other heating and cooling systems, their greater efficiency means the investment can be recouped in two to ten years. After that, energy and maintenance costs are much less than conventional heating and air-conditioning systems.
When Geothermal Heat Pump systems are installed in commercial buildings, the state-of-the-art designs are extremely competitive on upfront costs when compared with cooling towers and boilers, and they have lower energy and maintenance costs.
In addition to their cost effectiveness, Geothermal Heat Pump systems offer aesthetic advantages, quiet operation, free or reduced-cost hot water, improved comfort, and a host of other benefits.
What Is a Geothermal Heat Pump?: Geothermal heat pumps are viable nationwide. The technology relies on the fact that the Earth (beneath the surface) remains at a relatively constant temperature throughout the year, warmer than the air above it during the winter and cooler in the summer, very much like a cave. The geothermal heat pump takes advantage of this by transferring heat stored in the Earth or in ground water into a building during the winter, and transferring it out of the building and back into the ground during the summer. The ground, in other words, acts as a heat source in winter and a heat sink in summer. Through a system of underground (or underwater) pipes, they transfer heat from the warmer earth or water source to the building in the winter, and take the heat from the building in the summer and discharge it into the cooler ground. Therefore, Geothermal Heat Pumps don't create heat; they move it from one area to another.
The system includes three principal components:
Geothermal earth connection subsystem
Geothermal heat pump subsystem
Geothermal heat distribution subsystem.
Earth Connection: Using the Earth as a heat source/sink, a series of pipes, commonly called a "loop," is buried in the ground near the building to be conditioned. The loop can be buried either vertically or horizontally. It circulates a fluid (water, or a mixture of water and antifreeze) that absorbs heat from, or relinquishes heat to, the surrounding soil, depending on whether the ambient air is colder or warmer than the soil.
How Do They Work?: Simply put, a Geothermal Heat Pump works much like the refrigerator in your kitchen, with the addition of a few extra valves that allow heat-exchange fluid to follow two different paths: one for heating and one for cooling. The Geothermal Heat Pump takes heat from a warm area and exchanges the heat to a cooler area, and vice versa. The beauty of such a system is that it can be used for both heating and cooling-doing away with the need for separate furnace and air-conditioning systems-and for free hot water heating during the summer months. Conventional ductwork is generally used to distribute heated or cooled air from the geothermal heat pump throughout the building.
Benefits of a Geothermal Heat Pump System: Low Energy Use - The biggest benefit of Geothermal Heat Pumps is that they use 25-50% less electricity than conventional heating or cooling systems. This translates into a Geothermal Heat Pump using one unit of electricity to move three units of heat from the earth. According to a report by Oak Ridge National Laboratory, statistically valid findings show that the 4,003-unit Geothermal Heat Pump retrofit project at Fort Polk, Louisiana, will save 25.8 million kilowatt-hours (kWh) in a typical meteorological year, or 32.5% of the pre-retrofit whole-community electrical consumption. This translates to an average annual savings of 6,445 kWh per housing unit. In addition, 100% of the whole-community natural gas previously used for space conditioning and water heating (260,000 therms) will be saved. In housing units that were all-electric in the pre-retrofit period, the Geothermal Heat Pumps were found to save about 42% of the pre-retrofit electrical consumption for heating, cooling, and water heating.
Free or Reduced-Cost Hot Water: Unlike any other heating and cooling system, a geothermal heat pump can provide free hot water. A device called a "desuperheater " transfers excess heat from the heat pump's compressor to the hot water tank. In the summer, hot water is provided free; in the winter, water heating costs are cut roughly in half. Many residential systems are now equipped with desuperheaters. A desuperheater provides no hot water during the spring and fall when the geothermal heat pump system is not operating; however, because the geothermal heat pump is so much more efficient than other means of water heating, manufacturers are beginning to offer "full demand" systems that use a separate heat exchanger to meet all of a household's hot water needs. These units cost-effectively provide hot water as quickly as any competing system.
Year-Round Comfort: While producing lower heating bills, geothermal heat pumps are quieter than conventional systems and improve humidity control. These features help explain why customer surveys regularly show high levels of user satisfaction, usually well over 90 percent.
Design Features: Geothermal heat pump systems allow for design flexibility and can be installed in both new and retrofit situations. Because the hardware requires less space than that needed by conventional HVAC systems, the equipment rooms can be greatly scaled down in size, freeing space for productive use. And, geothermal heat pump systems usually use the existing ductwork in the building and provide simultaneous heating and cooling without the need for a four-pipe system.
Improved Aesthetics: Architects and building owners like the design flexibility offered by Geothermal Heat Pumps. Historic buildings like the Oklahoma State Capital and some Williamsburg structures use Geothermal Heat Pumps because they are easy to use in retrofit situations and easy to conceal, as they don't require cooling towers.
Geothermal Heat Pump systems eliminate conventional rooftop equipment, allowing for more aesthetically pleasing architectural designs and roof lines. The lack of roof top penetrations also means less potential for leaks and ongoing maintenance, and better roof warranties. In addition, the aboveground components of a Geothermal Heat Pump system are inside the building, sheltering the equipment both from weather-related damage and potential vandalism.
Low Environmental Impact: Because a Geothermal Heat Pump system is so efficient, it uses a lot less energy to maintain comfortable indoor temperatures. This means that less energy-often created from burning fossil fuels-is needed to operate a Geothermal Heat Pump. According to the EPA, geothermal heat pumps can reduce energy consumption-and corresponding emissions-up to 44% compared to air-source heat pumps and up to 72% compared to electric resistance heating with standard air-conditioning equipment.
Low Maintenance: According to a study completed for the Geothermal Heat Pump Consortium (GHPC), buildings with Geothermal Heat Pump systems had average total maintenance costs ranging from 6 to 11 cents per square foot, or about one-third that of conventional systems. Because the workhorse part of the system-the piping-is underground or underwater, there is little maintenance required. Occasional cleaning of the heat exchanger coils and regularly changing the air filters are about all the work necessary to keep the system in good running order.