Ground source or geothermal heat pumps are based on pipes buried in the underground or submerged in a well or other body of water.
Underground temperatures – like cave temperatures - are a lot more stable and less extreme than above ground air temperatures, and geothermal heat pumps have the ability of benefiting from it. They can produce 3, 4 or more times kWh of heat (or cold) than the electricity they consume, using underground temperatures (even when above ground temperatures are freezing).
Do ground heat pumps make sense in energy efficient single-family homes?
The short answer is no. They only make sense in large buildings. See, for more details:
New energy efficient homes,
Heating in new homes
Contrary to air-source heat pumps, geothermal heat pumps do not need to resort to electric-resistance heaters, when outdoor temperatures are freezing .
Closed and open-Loop Designs
Geothermal heat pumps may have a closed-loop or an open-loop design.
The closed loop design uses a solution of water and an antifreezing.
The open-loop design doesn't circulate the anti-freezing solution.
Ground and loop Configuration
The length of the underground loop and its configuration depend on cost considerations, the layout of the site where the heat pump is going to be installed, and on landscape, climate and soil conditions and availability.
Horizontal loops are generally the most economical.
Vertical loops are more compact and less disruptive of the surrounding landscape.
The existence of a convenient rock shell near the building (see picture at right) can make vertical-compact loops a good choice.
water Source heat pump loops
Water source heat pumps have their loop submerged in the water of a lake, river and more commonly in a well.
Images credit: Danfoss