Ground source heat pumps can extract energy from the ground or water using a closed loop or open loop collector. The size of the array is dependent on a number of factors including but not limited to the peak heating and cooling loads and usage of the building.
The most common design is to use a horizontal collector buried in a trench 1.2m deep x 1m wide. This method does require a large amount of ground and can not be used to build on. A typical 3 bedroom house would require 300-400m of pipe.
If space is an issue then a vertical borehole can be drilled. The bore hole is drilled to depths of up to 150m for residential properties. One of the most important factors with drilling is to ensure a thermal grout is pumped in to remove air from around the bore hole pipe. A lot of companies do not do grout and rely on the water table which will vary throughout the year. This will cause inefficiencies in the heat pump and potential system failure.
The slip trench design uses a 200mm wide bucket to install a single collector pipe. Trenches must be a minimum of 1m apart.
The open trench design uses a 1m wide bucket to install the collector pipe either side of the trench. Trenches must be a minimum of 1m apart.