Feature Report: Geothermal Energy, the Earth’s Heat

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Very Low-Temperature Geothermal Energy: Heat Pumps and Ground Source Collectors

Very low-temperature geothermal energy is tapped by small installations for a specific area or individual home. For this, heat pumps and buried pipes (“loops”) or boreholes are used.

A house can be heated by harnessing heat from underground. © THINKSTOCK

The heatIn the field of statistical thermodynamics today, heat refers to the transfer of the thermal agitation of the particles making up matter... from subsurface rocks or water tables close to the surface with temperatures of under 40°C can be captured and used to heat homes. This is called very low-temperature geothermalDescribes the technology used to tap subsurface heat to produce energy... energy.

Homeowners can recover heat from their yards to supply an underfloor heating system.

Buried ground source collectors (“loops”) are used to recover heat from underground, in conjunction with heat pumps. This type of installation is often affordable for homeowners.

Some ground source collectors are buried horizontally at shallow depths of 0.60 to 1.20 meters and require a surface area of one-and-a-half to two times the surface area of the building to be heated. In built-up areas, where available land is often restricted, vertical ground source collectors extending to depths of 30 to 150 meters or boreholes are used. In both cases, a mix of water and antifreeze circulates through a system of coiled pipes. The hot water flows to the surface and drives a heat pump. The heat recovered this way is usually used to supply underfloor heating systems. 

Heat Pumps

Heat pumps can recover heat from water contained in water tables less than 100 meters underground with temperatures of 15 to 40°C. If correctly installed, these systems can leverage this low temperature.

Inside the pumps, the warm to hot water boils a fluid with a boiling point of less than 0°C, for example ammonia (-33°C). The fluid is converted to gas and compressed using an electric compressor. This heats the gas, which transfers heat to a system of pipes linked to radiators. Once it loses its heat, the gas liquefies and returns to the start of the loop.

60 centimeters: the depth from which heat can be recovered

Heat pumps do require electricityForm of energy resulting from the movement of charged particles (electrons) through a conductor..., but they provide more thermal energy than they use.  Coefficients of performance have been developed to inform consumers about the amount of energy produced by a heat pump versus the amount used. Most heat pumps sold in retail outlets have a coefficient of performance of 3; that means that for each kWh of electricity they use, they supply 3 kWh.