A few metres below the surface, ground temperature stays nearly constant through the year, typically somewhere between about 5 and 12°C (41 and 54°F) in populated parts of Canada, depending on location. Ground-source heat exchange, often called geothermal or geoexchange, uses that stable temperature as a heat source in winter and a heat sink in summer. Heat pumps lift the temperature to useful levels for heating, or reject heat to the ground for cooling.
Because the source temperature does not plunge on a January night the way outdoor air does, ground-source heat pumps maintain capacity and efficiency in cold weather. That makes them attractive for electrifying heating in Edmonton, Calgary, Winnipeg and other cold climates. The trade-off is a higher first cost and a design that must get the ground side right, because a borefield is very expensive to fix once installed.
System types
| Type | Description | Typical commercial use |
|---|---|---|
| Vertical closed loop | Boreholes, often 60 to 180 m (200 to 600 ft) deep, with plastic U-tubes and grout | Most common for commercial sites with limited land |
| Horizontal closed loop | Pipes in trenches 1.5 to 3 m deep | Low-rise buildings with large open land |
| Open loop (groundwater) | Water pumped from a well, through a heat exchanger, returned to an aquifer | Sites with good aquifers and regulatory approval |
| Surface water loop | Coils in a lake or pond | Lakeside sites |
| Foundation or pile loops | Loops cast into foundation piles | New construction with deep foundations |
Closed loop systems circulate water or an antifreeze solution in sealed piping. Open loop systems can be very efficient but depend on groundwater quality, quantity and provincial water licensing.
How the building connects
The ground loop typically connects to:
- Distributed water-to-air heat pumps on a common building loop, a classic water-source heat pump system.
- Central water-to-water heat pumps producing hot and chilled water for hydronic distribution, radiant systems or air handlers.
- Hybrid plants, where the borefield is combined with a boiler, cooling tower, dry cooler or air-to-water heat pump to reduce the size of the borefield.
Designing the borefield
Borefield design is a long-term heat transfer problem. The ground behaves like a large thermal battery. Each year, heat is withdrawn in winter and added in summer. If those amounts are unbalanced, the ground around the borefield slowly cools or warms over many years, and loop temperatures drift until the heat pumps lose capacity.
Key inputs
- Hourly or monthly building loads for heating and cooling over a full year, ideally from an energy model.
- Peak loads and their duration.
- Ground thermal conductivity and undisturbed temperature, measured by a thermal response test.
- Borehole thermal resistance, which depends on pipe size, spacing, and grout conductivity.
- Borehole spacing and layout, since closely spaced boreholes interfere with each other over time.
- Allowable minimum and maximum loop temperatures set by the heat pump selection and antifreeze.
- Design life, commonly 20 years or more of simulated operation.
Specialized software uses these inputs to size total bore length and predict loop temperatures over the design life.
Thermal response testing
A thermal response test (TRT) is performed on a test borehole drilled on site. A known amount of heat is injected into a circulating loop for typically 48 hours or more, and the temperature response is used to calculate ground thermal conductivity and borehole resistance. A TRT reduces uncertainty and often allows a smaller, less expensive borefield than conservative assumptions would.
Ground thermal balance in Canada
Most Canadian commercial buildings are heating dominated, especially in the Prairies. Over many years, a borefield sized only for peak heating can cool the ground progressively. Strategies to manage imbalance:
- Supplemental heat: a boiler, air-to-water heat pump or solar thermal input covers peak heating or recharges the ground.
- Heat recovery: capturing cooling loads from interior zones, server rooms or refrigeration and sending them to the ground in summer.
- Hybrid sizing: sizing the borefield for most of the annual heating energy rather than the peak, which reduces drilling cost substantially.
- Wider borehole spacing to limit long-term interference.
Buildings with large internal loads, such as offices with high occupancy or data rooms, may be cooling dominated and face the opposite problem, solved with a cooling tower or dry cooler to reject excess heat.
Codes and standards
The CSA C448 series covers the design and installation of earth energy systems in Canada for commercial and residential applications, including loop materials, joining, grouting, pressure testing and antifreeze. Provincial rules also apply: some provinces regulate geothermal boreholes under well or groundwater legislation, open loop systems usually require water licences, and some restrict certain antifreeze solutions. Requirements vary by province and municipality, so confirm them with the AHJ and the environmental regulator early in design.
Antifreeze and loop fluids
In heating-dominated climates, loop temperatures often fall below freezing during peak heating, so antifreeze is needed. Propylene glycol, ethanol and methanol solutions are used, with different environmental, toxicity, heat transfer and viscosity characteristics. Antifreeze reduces heat transfer and increases pumping energy, so concentration should be chosen for the actual minimum loop temperature. See glycol systems.
Costs and economics
Ground-source systems cost more upfront than conventional systems, mainly because of drilling. Operating costs are typically lower, maintenance is reduced since there is no outdoor equipment, and buried loops have very long service lives. Life-cycle cost analysis, rather than simple payback, is the right way to compare options. Hybrid designs often give the best economics by avoiding the most expensive marginal boreholes.
Frequently asked questions
How much land does a borefield need?
It depends on loads, ground conditions and borehole depth. Vertical borefields can be placed under parking lots, landscaping or even under the building in new construction. A preliminary sizing based on loads and typical ground properties gives an early estimate.
Does ground-source heat work in Edmonton or Winnipeg?
Yes. Ground temperatures remain far more stable than outdoor air, so heat pump capacity is maintained in cold weather. Design must address the heating imbalance over the long term.
How long do ground loops last?
High-density polyethylene ground loops installed and tested properly are expected to last many decades, far longer than the heat pumps connected to them.
Our geothermal systems team can help assess feasibility and borefield sizing for a specific site.
Key takeaways
- Ground-source systems use stable ground temperatures to keep heat pump capacity high in cold weather.
- Vertical closed loops are most common for commercial sites; open loops need suitable aquifers and licences.
- A thermal response test and long-term simulation are the foundation of borefield design.
- Heating-dominated Canadian buildings need a strategy for long-term ground thermal balance.
- CSA C448 and provincial regulations govern design and installation; check requirements early.
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