Ground source heat pump (also referred to as geothermal heat pump) systems provide space heating and cooling, and, in some cases, hot water for residential and commercial buildings. The technology uses an indoor heat pump unit and a heat exchanging ground loop buried underground (or underwater) to transfer thermal energy between and amongst the ground and the building. The variation in subsurface and/or groundwater temperatures remains constant across seasons—typically between 55°F, which allows ground source heat pump systems to reach coefficients of performance of between 3 to 6. When operating in heating mode, ground source heat pump systems transfer thermal energy from the ground (or groundwater) to the building; while when operating in cooling mode, the systems transfer thermal energy from the building to the ground (or groundwater).
Ground source pump systems are typically sized to provide 100% of the heating and cooling loads for a residential or commercial building. In some cases, though, these systems are sized below peak heating or cooling load – and installed with auxiliary electric resistance heat or cooling towers – to reduce installed costs.
There is significant variation in how the ground loop component is designed and installed, which affects project costs and efficiencies.
- Closed-loop systems use a ground loop (typically made of polyethylene or PVC piping) that circulates water or antifreeze to exchange heat with the ground or a groundwater source. For closed-loop residential and smaller commercial systems, horizontal “slinky” configurations are often used. Vertical configurations, which can have column wells of up to 400 feet deep, are often used for large commercial systems. Closed-loop systems can also be submerged in bodies of water.
- Open-loop systems circulate water for heat extraction and rejection directly from local groundwater sources. This can reduce the installed cost due to less piping and enhance system efficiency due to improved heat transfer.
- Ground source heat pumps systems can also be designed as direct exchange systems, which circulate a refrigerant through a copper pipe instead of a typical ground loop. Direct exchange systems are highly efficient at heat extraction and rejection.
Vertical closed-loop system operating in cooling mode.
Vertical closed-loop system operating in heating mode.
What are the Benefits of Ground Source Heat Pump Systems?
Ground source heat pump systems have several benefits, including:
- Low Operating Cost
- No Required Exposed Outdoor Equipment
- Level Seasonal Electric Demand
- No On-Site Combustion
- Long Life Expectancy
- Low Cost Integrated Water Heating
- No Supplemental Heat Required
- Low Environmental Impact
Who Can Benefit
While not a fit for all situations, ground source heat pump systems are applicable in both existing and new buildings. In general, their benefits are greatest in buildings with similarly sized annual heating and cooling loads, and those desiring independent climate control of many rooms. The systems can provide efficient heating and cooling of different zones simultaneously. In New York State, installations have ranged from single family homes to hotels and 500,000-square-foot office buildings.
Office buildings and schools are particularly good applications for geothermal heat pumps. These facilities have relatively high occupancy, fluctuating usage schedules, and widely varying heating and cooling requirements within individual zones (offices and classrooms) that are difficult to meet efficiently with conventional systems. Further, efforts to improve the efficiency of conventional systems employ control strategies that can add considerable cost and complexity to the systems, increase maintenance requirements, and often compromise occupant comfort.
Helpful Information Links
The Geothermal Exchange Organization
The Geothermal Exchange Organization (GEO) is the voice of the geothermal heat pump industry in the United States.
International Ground Source Heat Pump Association
The mission of the International Ground Source Heat Pump Association and its membership is to promote the use of ground source heat pump technology worldwide through communication and education.
New York Geothermal Energy Organization (NY-GEO)
The New York Geothermal Energy Organization is a non-profit organization representing ground source heat pump (GHP) installers, manufacturers, distributors, general contractors, engineers, renewable energy consultants and industry stakeholders from throughout New York State