The Scoop on Geothermal Energy and Ground Source Heat Pumps

People have known since ancient times that the Earth’s interior is very hot. The temperature of the Earth’s core is estimated to be between 3000 and 5000o C (scientists are still not sure what the exact temperature is). This heat is generated by the slow breakdown of radioactive elements, and by the immense gravitational pressures acting on the rocks and minerals of the Earth’s interior. Temperatures in excess of 500o C can be found in the Earth’s crust just a few thousand metres below the surface, but geothermal heat right at the surface of the land is barely detectable.

Geothermal heat has been used to heat homes and businesses on a commercial scale since the 1920s. In most cases, communities take advantage of naturally occurring geysers, hot springs, and steam vents (called fumaroles) to gather hot water and steam for heating. Geysers and fumaroles occur when ground water seeps through cracks and comes in contact with volcanically heated rocks. In Iceland for instance, wells are drilled into volcanic rocks to extract hot water and steam. The hot water or steam is carried to communities in insulated pipes and used to heat homes and businesses. In some cases, the water is superheated (heated under pressure to temperatures greater than 100o C). Superheated water quickly turns to high-pressure steam, which can turn high-speed turbines that drive electrical generators.

GROUND SOURCE HEAT PUMPS

The temperature of the soil below about 2 metres remains constant regardless of the weather or season. In most places throughout southern Canada, soil temperatures at this depth hover between 5 and 10o C. The difference between air and deep soil temperatures can be used for heating and cooling in a very efficient manner, with a ground source heat pump, also called a geothermal heat pump.

at A ground source heat pump works the same way your refrigerator does. Like your fridge, a heat pump uses a compressor, lengths of sealed tubing for gathering and dispersing heat (heat exchangers), and a gas called the refrigerant. An essential part of the heat pump is the network of tubes buried deep in the soil near the home. The compressor motor, located inside the house, circulates refrigerant around this network. Heat from the surrounding soil warms the liquid refrigerant in the buried tubes, changing it to a gas. The refrigerant gas enters the compressor, which squeezes it, raising its pressure and temperature. The hot refrigerant circulates through radiators inside the house, releasing the heat collected from the soil to the inside of the house. This process changes the refrigerant back into a liquid and the process starts again.

By reversing the flow of the refrigerant, the heat pump system can cool the house in summertime. Heat collected from inside the house can be released back into the cool soil, resulting in a highly efficient air conditioning system for the home. A ground source heat pump requires some electricity to run the compressor. In an efficient, well-insulated home, this electricity could be easily supplied by a rooftop solar panel.- re-energy.ca-


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