MISSION

Renewables

Intro

Ground Source Heat (GSH)

The earth, a few metres below our feet, keeps a constant temperature of about 11-12C/ 55ƒF throughout the year. Because of the ground's high thermal mass, it stores heat from the sun during the summer. Ground source heat pumps (GSHP) can pump this heat from the ground into a building to provide space heating and, in some cases, pre-heating domestic hot water. For every unit of electricity used to pump the heat, 3-4 units of heat are produced.

In summer, the soil temperature is cooler than the outside air. In winter, it's warmer. A GSH pump can use this constant temperature to heat and cool your home very efficiently. There's no flame, no flue, no odour and no pollutants.

How does it work?
There are three important elements to a GSHP: Ground loop - comprises lengths of plastic pipe buried in the ground, either in a borehole or a straight horizontal and spiral horizontal (or 'slinky'). Each has different characteristics allowing you to choose the most suitable for your property. The pipe is a closed circuit and is filled with a mixture of water and antifreeze, which is pumped round the pipe absorbing heat from the ground.

Horizontal trenches can cost less than boreholes, but require greater land area. For slinky coil, a trench of about 10m length will provide for about 1kW of heating load.

Heat pump - although we may not know it, heat pumps are very familiar to us. Fridges and air conditioners are all examples. A heat pump works by using the evaporation and condensing of a refrigerant to move heat from one place to another. In this case, the evaporator (e.g. the squiggly loop in the cold part of your fridge) takes heat from the water in the ground loop; the condenser (the hot thing on the back of your fridge) gives up heat to a hot water tank that feeds the distribution system.

A compressor, which uses electricity, (this is what makes the noise in your fridge) moves the refrigerant around the heat pump. It also compresses the gaseous refrigerant to increase the temperature at which it condenses, to that needed for the distribution circuit.

Heat distribution system - consists of underfloor heating or radiators for space heating and water storage for hot water supply. Some systems can also be used for cooling in the summer.

Cost-Effective Heating
In the heating season, a ground-source heat pump supplies three to four units of heat to your home for every unit of electrical energy required to operate the system. So you get two to three kilowatt hours (kWh) of free energy for every one kWh of electrical energy you pay for. In other words, a ground-source heat pump is 300% to 400% efficient.

There are several different types of GS Heating configurations. The type of one you pick is dependent on the surrounding landscape your house is built in and the typical climate you experience year round.

How much will a system cost me?
The installed cost of a GSHP, for a professional installation, ranges from about £800-£1,200 per kW of peak heat output, excluding the cost of the distribution system. Trench systems tend to be at the lower end of this range. The installed cost of a typical 8kW system would therefore vary between £6,400-£9,600 plus the cost of the distribution system. Note that costs will vary and the cost for a system for your home may differ.