How is geothermal energy used?

The principal use of geothermal energy in Canada today is to heat and cool residences and commercial and institutional buildings. In the most common application, devices called heat pumps extract near-surface thermal energy from buried pipes or coils and distribute it through the building. The heat pump, which operates on the same principle as the compressor in a refrigerator, can also reverse the process to provide cooling. The Earth Energy Society of Canada estimates there are more than 30,000 residential heat pump installations in Canada and another 5,000 in schools, hospitals, prisons and commercial buildings.

There are two main types of geothermal heat pump systems, known as “closed loop” or “open loop.” A closed-loop system continuously recirculates a fluid – typically a mixture of antifreeze and water in Canada, but potentially plain water or even air. An open-loop system draws in water from an underground aquifer or from a nearby water body and then discharges the water back into the aquifer or water body. Open-loop systems are generally less expensive, but they require a suitable water supply, are subject to mineral buildups, and must be installed in accordance with environmental regulations.

The heating and cooling may be distributed through the building by circulating the fluid as in a conventional hot-water system. However, in larger buildings and where air-conditioning is required, the heating or cooling is typically transferred to forced-air ducting through heat exchangers. Heat exchangers can also be used to pre-heat water for the hot water system. Some heat pump systems can meet all or most of a building’s hot water requirements. Other potential uses of such systems include grain drying, ice making and snow melting. A curling rink in Oliver, B.C., halved its energy bills, and eliminated use of hazardous ammonia refrigerant, when it installed geothermal heat pumps for both heating and ice making. An industrial park in Springhill, N.S., with access to 21° C water in an abandoned coal mine, has saved hundreds of thousands of dollars in heating and cooling costs.

In Toronto, more than 100 buildings in the Enwave District Heating Project – which includes the Air Canada Centre, the Metro Convention Centre and major office towers – use an open-loop system drawing water from Lake Ontario through heat exchangers to provide air conditioning. This system reduces electricity requirements and greenhouse gas emissions substantially, and it eliminates the need for refrigerants that can affect the ozone layer in the atmosphere.

A related system, Underground Thermal Energy Storage (UTES), uses underground reservoirs to store heat during the summer and to provide heat during the winter. Where suitable reservoirs are available, UTES can provide significant energy savings. Since the 1980s, this technology has been used by large facilities such as Carleton University in Ottawa, the municipal centre in Scarborough, Ontario, and the Hydro-Québec Administrative Centre in Laval.

In many parts of British Columbia, and a few adjacent areas of Alberta and Yukon, higher-temperature geothermal energy is close enough to the surface for potential uses in heating buildings, greenhouses and fish farms. The principal use today is for bathing at or near hot springs. Several locations in the coastal mountains have been identified as potential sites for geothermal electric generating stations, and the Western GeoPower Corp. $340-million, 100-megawatt project could be in production by 2007 at Meager Creek about 90 kilometres northwest of Whistler. The project has drilled wells two kilometres deep that encountered temperatures about 255° C, which will generate steam to drive turbines and generators at the surface; the condensed steam will be returned to the same geological formation. The site has the potential eventually to produce an additional 100 megawatts.

Multiple heat pumps and hot water pre-heater at a federal correctional facility, Truro, Nova Scotia

Geothermal heat pump systems
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The Walton Street Plant in downtown Toronto is part of the EnWave system that uses cold water from Lake Ontario to cool many commercial and institutional buildings.