Ground Source Heat pumps
Ground source heat pumps work by using heat stored in the ground from the sun's solar radiation to supply all of the energy required for a buildings heating and hot water system.
The top 15 metres of the Earth's surface maintains a relatively constant temperature of approximately 12 degrees Centigrade. This energy can be used to heat buildings indirectly. Pipe is buried in the ground, either in a borehole or a horizontal trench. The pipe is usually a closed circuit and is filled with a mixture of water and antifreeze, which is pumped round the pipe, absorbing heat from the ground. In winter the ground is warmer than the air and buildings above. The anti-freeze mixture absorbs heat from the ground, which is then concentrated and transferred to the buildings. This heat can be used to heat domestic water and a low temperature heating system such as underfloor heating, fan convectors and correctly sized panel radiators.
The efficiency of a ground source heat pump is measured in Coefficient of Performance (CoP). This is the ratio of units of heat output for each unit of electricity used to drive the compressor and pump for the ground loop. A CoP of 4 means that for every kilowatt of electricity put in, you get 4 kilowatts of energy in the form of warm water. The flow temperature of the warm water is typically between 35 degrees Centigrade and 45 degrees Centigrade; much lower than achieved by a domestic boiler. The units can reach higher temperatures, but the CoP is then compromised. Keeping the temperature at the lower end of the scale ensures the system operates more efficiently.
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