Ground source heat pumps: the basics in plain words
A ground source heat pump uses the steady temperature of the earth as its heat source and sink, moving heat between the ground and the house with an electric compressor. Ground source, geothermal and geoexchange all describe the same residential technology, and the quotes you see will mix those terms freely.
What do the different names mean?
The names overlap, which confuses first-time buyers. Ground source heat pump, often shortened to GSHP, is the technical term. Geothermal heat pump is the common marketing name, and geoexchange is the industry term used in parts of Canada. All three refer to a heat pump that exchanges heat with the ground or groundwater. A water-source heat pump is related and uses a pond or a well as the source. The guide to how geothermal heating works explains how the home meaning differs from deep geothermal power.
An air-source heat pump, by contrast, draws heat from outdoor air, and the trade-offs between the two are in air source versus ground source.
What are the basic parts?
- Ground loop. Buried pipe carrying a water and antifreeze mix between the ground and the heat pump. Layout types are compared in horizontal and vertical ground loops.
- Heat pump unit. A cabinet indoors containing the compressor, two heat exchangers and a reversing valve for heating and cooling.
- Circulation pump. Keeps the loop fluid moving. It uses a small share of the energy the system consumes.
- Distribution. Ducts with an air handler, or floor and radiator piping, that carries the heat through the house.
- Controls. A thermostat and the unit's control board that manage staging, the loop and any backup.
How is the size of a system described?
Capacity is given in tons or kilowatts. One ton of heat pump capacity equals 12,000 British thermal units per hour, or about 3.5 kilowatts of heat. A typical house needs a unit sized to its heat loss at the design temperature, which comes from a room-by-room calculation, not from floor area alone. The method is described in heat pump load calculation.
The loop is sized separately, by the heat it must exchange with the ground over the year. Drilling depth and borehole spacing follow from the ground's thermal properties, as shown in geothermal borehole depth and spacing.
How efficient is a ground source system?
Efficiency is the coefficient of performance, or COP: heat delivered divided by electricity used. Ground source units are commonly quoted with seasonal COPs somewhere in the range of three to five, depending on the loop temperature and the heating system. Low-temperature distribution such as radiant floors raises the figure. Published ratings follow test standards, and your real result depends on the design and the house. The mechanics are covered in how ground-source heat pumps work.
What should a first-time buyer know?
The ground source part is the expensive part, so ask for the loop design to be written out with its length, depth and the design temperatures behind it. A house that is tight and well insulated needs a smaller loop, and so costs less. Check that the contractor and the driller are certified in your province, and that the loop will be pressure-tested and flushed before it is buried. Then compare costs and expected savings for your house, starting with geothermal heat pump cost in Canada.
Quick answers
Is a ground source heat pump the same as a geothermal heat pump?
In a home setting, yes. The names ground source, geothermal and geoexchange describe a heat pump with a buried loop or a groundwater connection.
What does one ton of heat pump capacity mean?
A ton is 12,000 British thermal units per hour, about 3.5 kilowatts of heat output. Most houses need a unit sized by a heat-loss calculation, not by a rule of thumb.
How warm is the ground in Canada?
Below the frost line it stays near the average yearly air temperature of the site, with little change through the season. The ground temperature guide gives typical figures.
What is the COP of a ground source heat pump?
Commonly quoted seasonal figures run from about three to five, depending on the loop, the climate and the distribution system. The manufacturer's data and the design assumptions give the real figure.