least talked about forms of renewable energy. And yet, we have utilised it to power everyday operations since the 1940’s¹. Geothermal energy uses the earth’s high temperatures for heat particularly during winter and it can also use the earth as a heat sink for cooling in the summer². Apart from it being a tried and tested technology, it is much more efficient compared to other forms of renewable energy. Specifically, geothermal heat pumps can provide clean heating and cooling without producing any noise or disrupting the landscape and also cut your energy bills by up to 70%³. It therefore makes sense that geothermal energy is used in all 50 States in the United States, with 80,000 installed each year. About 27,000 units are installed in Sweden every year and geothermal heat pumps were the heating system of choice for new houses in Finland, their market share exceeding 40% in 2006-2011².
So how does this popular technology work?
A geothermal heat pump, otherwise known as a ground source heat pump, uses the heat that is found underground by pumping water through it. Depending on your geographical location, ground temperatures will range from 7 to 21°C. Just like a cave, this (under)ground temperature is warmer than the air above it during the colder months and then cooler during the summer months¹. The heat pump can then increase the temperature and use it to heat your home or water. It runs on electricity but it uses much less electricity compared to what is needed to produce that heat. It works very much like a boiler but the heat pump uses air from the ground rather than burning fuel to generate heat. In terms of energy use though, a heat pump with mid-range efficiency uses only a third of the energy needed by a boiler to produce the same amount of heat⁴. It is important to get the design and installation of a geothermal heat pump right as this will greatly affect how efficient it is.
A geothermal heat pump includes the following components: what is called a “ground loop” which is essentially a set of interlinked water pipes which are buried underground and a heat pump which is installed at ground level. Some space is needed to install this technology; this must also include a way for digging machinery to access this space. The size of the ground loop depends on the size of your house as well as how much heat you will need. The greater the size of the loop, the more space the heat pump requires, so that is a further consideration you need to take into account if you are considering whether to install a geothermal heat pump⁵.
The heat pump consists of an evaporator, a compressor and a condenser. A mixture of water and anti-freeze is pumped though the ground loop network of water pipes which are underground. The heat pump then pumps out this water mixture and extracts the heat from it so it can be transferred to your home heating system, at the same time increasing the temperature. What is great about a geothermal pump is that it can increase the temperature quite substantially – between 1.5 and 4 times. This means that if the water extracted from the ground is 12°C, this can reach anywhere between 18 and 48°C⁵. The water can then be used for taking hot showers and baths while the heat can be sent to radiators. The leftover heat can be stored in hot water cylinders and used later on⁵. The direction of the water mixture determines whether the heat is moving into the house or being pulled out of it to lower temperatures³.