Geothermal energy is the heat of the earth. The temperature underground remains constant throughout the year come rain or shine. A Geothermal Heating/Cooling system simply transfers heat to and from the earth to provide a more efficient, affordable and environmentally friendly method of both heating and cooling.

Green Energy

Geothermal systems are amongst the most environmentally friendly heating and cooling systems available today. They produce zero localised emissions, so there is no air pollution or contribution to global warming. They use the earth’s free and renewable energy and they operate at a typical 400% overall efficiency – that means for every unit of energy they use, they produce 4 more. Geothermal energy is an unlimited resource - the earth absorbs 47% of the sun’s energy, which amounts to 500 times more energy than is required by mankind each year. A 1m2 area of ground typically absorbs 1100kW per annum.

Geothermal or ground coupled heating / cooling technology can be a very effective way of achieving all or part of the 10% renewable energy target set by the GLA in London for gaining Part L planning consents on large commercial developments.

Geothermal Heat Pumps

The technology behind ground Source Heat pumps is very simple. It uses the same technology as a refrigerator. During the heating cycle, low grade heat is transferred from the ground to a heat pump where the temperature is increased before being pumped to the heating distribution system. This can also be reversed to create cooling. Rather than making heat, they take existing heat from the distribution system and move it to a lower temperature source in the ground loop. The distribution system can be, amongst other methods, via under floor heating, conventional fan coils, chilled floors, chilled ceilings or forced air delivery for cooling.

Open Loop Installations

Open Loop systems involve pumping water from wells, boreholes, ponds, rivers or even the ocean. The water is passed through pipe work to the heat pumps directly or more commonly via a plate heat exchanger and then into the heat pump / chiller where heat is extracted or rejected. Where large commercial developments opt to exploit an underground aquifer, the Environment Agency will probably enforce an aquifer recharge scheme meaning they will direct that the spent water is returned to the same ground aquifer from which it came usually via an identical recharge borehole. The EA will need to see Tier 1,2 & possibly Tier 3 risk assessments involving thermal and hydrogeological modelling.

Commercial geothermal open loop system

Closed Loop Installations

A closed loop system is a continuous loop of buried pipe, which typically contains an environmentally friendly solution of water and anti-freeze. As the water is pumped through the pipe, the thermal energy from the earth transfers to the fluid in the pipe, changing the temperature by a few degrees. This temperature is then increased / decreased by passing it through a heat pump.
The loops can be laid vertically, horizontally or in ponds and lakes, although vertical is often the only realistic option on commercial installations or when there is limited space.

Commercial geothermal closed loop system

The pipes, if made of high-density polyethylene (PE100), will last for many many decades. Connections are usually made using electro-fusion couplers which protects against any leakage or contamination ( as with gas / water industry ).

With the loop pipes installed into the boreholes, it is of paramount importance to seal the borehole preventing cross-contamination of an aquifer ( remember the polluter pays ! ). This seal is usually achieved with a bentonite material. However, bentonite has very low heat transfer properties ( 0.73w/mK ) and when placing a loop in a moderate to high thermal conductivity (TC) strata, it is counter-productive to use just bentonite. By using thermally enhanced grouts ( high silica sand and bentonite mix ), higher TC values in excess of 2.2w/m/K can be achieved and more effective heat transfer can take place. A correctly designed grout can significantly increase the efficiency and therefore reduce the number or depth of boreholes required to service the load.