Practice

Ground-source heat pump

Also known as: Geothermal heat pump, GSHP

A heating and cooling system that exchanges heat with the earth — through buried loops of pipe carrying water/antifreeze — rather than with outdoor air. Earth temperature at modest depth is stable year-round (~50-60°F in temperate North America), making heat pumps far more efficient than air-source pumps in cold climates. Coefficient of Performance (COP) typically 3-5 — meaning 3-5 units of heat moved per unit of electricity used. Combined with renewable electricity, GSHPs can fully decarbonize home heating and cooling. Mature technology; widely adopted in Sweden, Switzerland, and increasingly elsewhere.

How it works

A ground-source heat pump moves heat between the building and the earth:

Heating mode — fluid in buried loop circulates through the earth (50-60°F in winter), absorbing heat; the heat pump compresses the working fluid to a higher temperature; delivers heat to the building
Cooling mode — reverse; absorbs heat from the building; releases it to the earth

The earth, at depths of 6-300+ feet, stays at a stable temperature — typically the average annual surface temperature. This stability is what makes GSHPs work in climates where air-source pumps struggle (cold winters when outdoor air is too cold to extract heat efficiently).

Loop configurations

Horizontal loops — buried 5-8 feet deep across a yard; cheaper but requires substantial yard area
Vertical loops (boreholes) — drilled 100-400 feet deep; typically 1-3 boreholes per residential system; works on small lots
Pond loops — submerged in a pond or lake; cheapest where water is available
Open-loop / standing-column wells — uses well water directly; high efficiency but limited applicability

Performance

Heating COP — 3-5 typical (3-5 units heat per unit electricity)
Cooling COP — 4-7 typical
Lifespan — heat pump unit 15-25 years; loop field 50+ years
Cost — high upfront ($20K-$50K residential typical); operating cost low

Why it matters

Heating and cooling are responsible for major portions of building energy use. GSHPs running on renewable electricity can:

Fully decarbonize building thermal loads
Reduce winter peak electricity demand (compared to electric resistance heat)
Reduce summer peak demand (compared to air conditioning)
Provide superior comfort

Adoption

Sweden — over 1 million GSHPs; ~50% of single-family homes
Switzerland, Austria — substantial adoption
Netherlands, Germany — growing
United States — modest but growing; ~120,000 new GSHPs annually
Canada — substantial growth driven by carbon-pricing and provincial programs

Considerations

Site requirements — adequate land or borehole-drillable subsurface
Cost barrier — high upfront; substantial savings over lifetime
Drilling expertise — geological surveys, qualified drillers needed
Building compatibility — works best with hydronic heat distribution; forced-air retrofitable

Sources

IEA Heat Pump Centre publications
Geothermal Heat Pumps, Ryan Jaynes (CRC Press, 2008)
DOE GSHP technical materials

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