Ground-source or geothermal heat pumps (GHPs) are similar to the air-source heat pumps, except that the source of heat is the ground instead of outdoor air.
Closed-Looped Systems
Horizontal
The horizontal type of installation is generally most cost-effective for residential installations, particularly for new construction where sufficient land is available. It requires trenches at least four feet deep.
Horizontal systems come in two types of layouts, the two pipes method and the slinky method.
Two Pipes
The most common horizontal layouts include:
Two Pipes Layout (Option 1) - One pipe buried at six feet, and another pipe buried at four feet.
Two Pipes Layout (Option 2) - Both pipes placed side-by-side at five feet in the ground in a two-foot wide trench.
The Slinky™ Method
The pipe is looped to allow more pipes in a shorter trench, which cuts down on installation costs and makes horizontal installation possible in areas not possible with conventional horizontal applications. Large commercial buildings and schools often use vertical systems because the land area required for horizontal loops would be prohibitive
Vertical
This type of system may be used when the soil is too shallow for trenching or when one does not want to disturb the existing landscaping.
For a vertical system, holes (approximately four inches in diameter) are drilled about 20 feet apart and 100 to 400 feet deep. Into these holes go two pipes that are connected at the bottom with a U-bend to form a loop. The vertical loops are connected with horizontal pipe (i.e., manifold), placed in trenches, and connected to the heat pump in the building
Benefits of GSHP
Click on the benefit listed below to find out more information.
- Low Energy Use
The biggest benefit of GHP's is that they use 20 to 50 percent less electricity than conventional heating or cooling systems. This translates into a GHP 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 GHP retrofit project at Fort Polk, LA, will save 25.8 million kilowatt-hours (kWh) in a typical year, or 32.5 percent of pre-retrofit whole-community electrical consumption. This translates to an average annual savings of 6,445 kWh per housing unit. In addition, 100 percent 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 GHP's were found to save about 42 percent 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 super heater 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.
- 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. Also, 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 GHP's. Historic buildings like the Oklahoma State Capital and some Williamsburg, Virginia, structures use GHPs because they are easy to use in retrofit situations and easy to conceal, as they don't require cooling towers.
GHP systems eliminate conventional rooftop equipment, allowing for more aesthetically pleasing architectural designs and roof lines. The lack of rooftop penetrations also means less potential for leaks and ongoing maintenance, and better roof warranties. In addition, the aboveground components of a GHP system are inside the building, sheltering the equipment both from weather-related damage and from potential vandalism.
- Low Environmental Impact
Because a GHP system is so efficient, it uses a lot less energy to maintain comfortable indoor temperatures. This means that less energy is often created from burning fossil fuels than is needed to operate a GHP. According to the EPA, geothermal heat pumps can reduce energy consumption and corresponding emissions up to 44 percent compared to air-source heat pumps, and up to 72 percent 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 GHP 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.
- Zone Heating and Cooling
These systems provide excellent zone space conditioning - different areas of the building heated or cooled to different temperatures simultaneously. For example, GHP systems can easily move heat from computer rooms (which need constant cooling) to the perimeter walls for winter heating in commercial buildings. School officials like the flexibility of heating or cooling just auditoriums or gymnasiums for special events rather than the entire school.
- Durability
Because GHP systems have relatively few moving parts, and because those parts are sheltered inside a building, they are durable and highly reliable. The underground piping often carries warranties of 25 to 50 years, and the GHP's often last 20 years or more.
- Reduced Vandalism
GHPs usually have no outdoor compressors or cooling towers, so the potential for vandalism is eliminated.