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 the 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.