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as-seen-from-space 331A critical element of a successful ground source heat pump installation is the ground loop design and construction.

Where enough land is available the most cost-effective and economical way to extract heat from the ground is from a number of horizontal loops of plastic pipe buried in the ground. The array is made up of a series of trenches normally 1 meter deep, around 4 meters apart and about 100-150 meters long. We install geothermal plastic collector pipe running along one side of the trench and back along the other to form a loop. Each loop is then connected to a manifold consolidating all the loops into just two pipes – one for the flow and other for the return. The flow and return pipes are then taken back through another trench to the house or plant room and connected to the heat pump. Once complete the system is flushed with clean water, flow-tested to make sure that all loops flow freely, pressure-tested, treated with a biocide to reduce the potential of microbial degradation, and finally filled with a mixture of glycol and water and purged of air. The glycol-water mixture is the antifreeze liquid that is the heat transfer fluid for the system which carries thermal energy from the ground to the heat pump.

We use a number of tools to help us design the system. The length of pipe that should be installed depends on a number of factors: the soil type and conditions, the capacity of the heat pump and the thermal load of the building. For example it is often possible to use a heat pump to heat the house in winter and an outdoor swimming pool in summer. However this puts an additional load on the ground array that must be compensated for by using more pipe and a larger area.

Often deficiencies, short cuts or unwise cost-savings in the design of the ground array manifest themselves only after three or four years of use. Too small or too compact a ground array and the ground will cool and eventually freeze due to over extraction. Any reduction in average ground temperature will reduce the efficiency of the heat pump system.

Almost equally important to the sizing of the array is the flow through the pipes. Design criteria need to include pressure losses and the turbulence in the pipes and manifolds which effects collector performance and the size of the required circulation pump.

Our ground array designs include the highest quality manifolds which allow for individual loop isolation and provide individual flow meters and individual balancing valves. These ensure optimal efficiency from the collector array by maximising performance of the ground loops and minimising circulation pumping capacity and operational cost.

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