How geothermal cooling works in summer
Geothermal cooling means running a ground-source heat pump in reverse: instead of pulling heat from the ground into the house, it moves heat out of the house and into the ground. The ground stays cooler than summer air, which is why the process uses less electricity than a typical air conditioner.
How does a geothermal heat pump cool a house?
The heat pump contains a reversing valve. In winter the refrigerant absorbs heat from the fluid circulating through the buried loop and releases it into the house. In summer the valve switches the direction, so the refrigerant absorbs heat from indoor air and passes it to the loop fluid, which carries it into the ground. The same equipment, the same loop and the same ductwork or radiant system do both jobs.
Below the depth where seasons reach, ground temperature stays close to the yearly average for the region, which in much of Canada is well under typical summer air temperatures. Our ground temperature by depth guide explains why. For the basic loop-and-heat-pump picture, see how ground-source heat pumps work.
Why is geothermal cooling efficient?
An air conditioner has to reject heat into outdoor air that is at its hottest exactly when you want cooling. A ground-source system rejects heat into cooler ground or water. The smaller the temperature gap the compressor has to work across, the less electricity it needs for the same amount of cooling, and that is the main saving. Fans and pumps still run, and total savings depend on the equipment, the climate and how much you cool.
There are two further effects. Cooling also dehumidifies the air, which many people find makes the same temperature feel more comfortable. And the system has no noisy outdoor condenser fan, so it is quieter outside. Efficiency ratings for cooling are published for each model, so compare them as you would any other equipment.
What is free cooling from the ground loop?
Some designs add a heat exchanger so that cool loop fluid can absorb heat from the building without the compressor running. This is often called free cooling or direct cooling, though pumps and fans still use some electricity. It works best when the loop fluid is cooler than the cooling target and in buildings with large cooling loads or hydronic cooling. In most Canadian houses, summers are short enough that the standard reversible heat pump is the usual choice. Ask a designer whether a direct-cooling option makes sense for your load rather than assuming it is included.
What are the limits of geothermal cooling?
Cooling adds heat to the ground, and in a climate with long heating seasons that is usually fine, since the winter draw takes more heat out than summer puts in. In a balanced design the ground recovers over the year. In a house with a very large cooling load and a small loop, ground temperatures can drift upward over the seasons, so the design should include both loads. A proper load calculation covers heating and cooling.
Cost is the other limit. Adding a ground loop only to replace an air conditioner rarely pays back, because the loop is the expensive part. The case is stronger when the same loop also provides heating, as set out in whether geothermal heat pumps are worth it and the cost guide.
The ground is also a store. At Drake Landing, Okotoks, summer heat was pushed deliberately into 144 boreholes to be used in winter. The borehole storage page shows that idea at community scale, while a home system with cooling is a much smaller version of the same principle.
Can summer waste heat make hot water?
Yes. Many ground-source units offer an optional component that captures some of the heat removed from the house during cooling and uses it to warm domestic hot water, which would otherwise go into the ground. That means water heating in summer can come close to free. See the guide on heat pump water heaters for the broader hot-water picture, and ask your installer whether this feature is available for the model you are considering.
Quick answers
Does a geothermal heat pump provide air conditioning?
Yes. Most ground-source heat pumps can reverse and cool the house in summer, moving indoor heat into the ground through the same loop used for heating.
Is geothermal cooling cheaper than air conditioning?
It typically uses less electricity per unit of cooling because the ground is cooler than outdoor air. The saving on cooling alone rarely repays the cost of the loop, so the case rests mainly on heating.
Does cooling damage the ground loop?
No. A properly designed loop handles both heating and cooling, and in colder regions the winter heat draw is usually larger than the summer heat added.
What is free cooling in a geothermal system?
It is a design in which cool loop fluid absorbs building heat through a heat exchanger without the compressor running. It uses only pumps and fans, but is not standard in all systems.