Moving heat from the earth into your house

What are the main parts?

There are three loops in one system. The first is the ground loop: plastic pipe full of water or a water and antifreeze mix, buried in trenches or boreholes. The second is the refrigerant circuit inside the heat pump cabinet, with a compressor, an expansion valve and two heat exchangers. The third is the house distribution, either ducted air or water running to floors or radiators.

A small circulation pump moves the ground loop fluid, and a controller decides when to heat, when to cool and how to handle domestic hot water.

How does the refrigerant cycle raise the temperature?

Ground loop fluid arrives at the heat pump a few degrees above freezing at the cold end of winter. In the first heat exchanger it warms a refrigerant that boils at a very low temperature, so the refrigerant turns to gas even from that modest source. The compressor squeezes the gas, which raises its pressure and temperature sharply. In the second heat exchanger the hot gas gives its heat to the house water or air and condenses back to liquid. The expansion valve drops the pressure, the refrigerant cools, and the cycle repeats.

The compressor is the main electrical load. Everything else is moving heat that was already there.

What is COP and why does it matter?

Coefficient of performance, or COP, is heat delivered divided by electricity used. A COP of 4 means one kilowatt-hour of electricity delivers four kilowatt-hours of heat, with three of those drawn from the ground. Ground-source units are often rated somewhere between 3 and 5 depending on test conditions, but the number you live with is the seasonal average, and it depends on the temperature the house needs.

Lower supply temperatures raise COP. That is why floor heating and large radiators pair well with ground-source units; see low temperature hydronic heating for the reasoning. A COP below 1 would be worse than a baseboard heater, and the pump is nowhere near that range in normal use.

Why the ground, and not the air?

Winter air in much of Canada can drop far below the temperature of soil a few metres down. Cold air gives the heat pump less to work with just when demand peaks, while the ground changes slowly. How stable it is, and at what depth, is explained in ground temperature by depth in Canada. The trade is that the ground loop costs money, as the cost guide lays out.

Where does Drake Landing fit in?

Drake Landing did not use ground-source heat pumps. It used the same kind of buried pipe differently: 144 boreholes of roughly 35 m stored heat collected by 800 solar collectors over summer, and the district loop delivered that heat to 52 homes through air handlers without any compressor in between. The ground acted as a battery rather than a source. How that differs from using the ground continuously is covered in geothermal vs solar heating.

A worked example with stated assumptions

Suppose a house needs 12,000 kWh of heat over a winter, and the system averages a COP of 4 over that period. The compressor and pumps would draw about 3,000 kWh of electricity, and roughly 9,000 kWh would come from the ground. If the same house used a resistance heater at a COP of 1, it would draw all 12,000 kWh. The numbers are round assumptions for illustration only; real seasonal values depend on the equipment, the loop temperatures and the supply temperature of the house system.

The comparison also explains why the heat pump is judged on efficiency at design conditions. A unit that meets the coldest day through a well-sized loop will hold its figure better than one forced to lean on electric backup elements. Related reading on cold-weather behaviour is in the cold climate heat pump guide.

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