There are different types of GSHPs, based on variations in the ground loop and indoor unit configuration.
Ground-loop heat exchanger. The ground loop is the heat exchange surface for your heat pump. A home will typically need several hundred to thousand feet of piping in the ground loop to provide enough heat in the coldest part of the year. Ground loops are divided into “closed” and “open” loops:
loop systems use a continuous loop of buried piping, typically made out of high density polyethylene. A closed-loop system will circulate a mixture of water and antifreeze that is not directly exposed to the environment. In New England, most closed-loop systems are installed in vertical configurations, in which the ground loop is run through multiple boreholes that are drilled several hundred feet deep (see below).
Some closed-loop systems are installed in horizontal configurations, in which the ground loop is run through multiple trenches approximately 5 ft. deep and around 300-400 feet long (see below).
2. Open-loop systems can be used where there is a source of groundwater available on the property from a well. Instead of circulating an antifreeze mixture, an open-loop system pumps groundwater into the indoor unit for heat extraction before returning the water to the ground. Open-loop systems are typically cheaper to install and more efficient (due to the more consistent year-round temperature of groundwater), though they require a readily-available source of clean groundwater and may require additional permitting or environmental review.
The configuration of the indoor unit will also vary depending on whether you use ductwork (forced air) or a water (hydronic) distribution system:
- A water-to-air system connects your indoor heat pump to a central air handler and uses your home’s existing ductwork to distribute heating and cooling throughout the home. Some modifications to your ductwork may be necessary to make it suitable for a ground-source heat pump.
- A water-to-water system connects your heat pump to your existing hydronic distribution system to provide heating. One or more air handlers (and perhaps some ductwork) is necessary to provide air conditioning.