Heat Sources & Collectors

Kensa ground source heat pumps are designed to extract renewable heat energy from a number of heat sources providing greater flexibility, affordability and compatibility with a range of applications.

Source types

Heat energy (typically from the sun) is stored in the ground and water all around us, at a constant temperature all year round. Ground source heat pumps are designed to extract this heat energy via an array of collectors (sometimes referred to as ground collectors or ground arrays).

Ground collectors can take many forms including a borehole in rock, slinky pipe in soil, or pond mat in a lake – Kensa has even designed systems to extract heat from sea water to provide heating to boats!


  • Water – If you are within reasonable reach (100m) of a water source (lake, stream, sea etc.) this should be your first option for a heat source due to water’s exceptional thermal conductivity and lower installation costs.
  • Cost – Borehole drilling is the most expensive of the ground array options, but is the quickest and less invasive option.
  • Geology – The ground conditions and therefore conductivity of the underlying geology will influence the cost of the ground array.
  • Area – As a general rule, a garden area of at least 40m x 12m is required. Smaller gardens can benefit from borehole collectors.

Key things to remember about ground source heat pump collectors:

  • Collector arrays are sized to meet the heat needs of the building, not the heat pump.
  • All collectors have broadly the same performance.
  • A buildings thermal efficiency affects heat pump performance more than the type of collector.

Surface Soil

1m below the surface the ground temperature remains a fairly constant 8-10°C all year round. This makes it an excellent renewable heat source for ground source heat pumps; indeed, surface soil was the first heat source used to work with ground source heat pumps, hence their name.

To extract the heat from surface soil, a network of ground collectors (or ground arrays), consisting of a series of pipes, is buried in the ground in trenches to a depth of 1 – 2m. Typically consisting of coiled pipe, collectors of this nature are referred to as ‘slinkies’.

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Solar energy stored in surface soil dissipates through the many rock layers beneath our feet to form a very stable heat source. Depending on the make-up of the geology, this can provide an excellent heat source for ground source heat pumps

Boreholes are the collectors used to extract heat energy from rock for ground source heat pumps. To extract the heat from the rock, straight pipes are installed down 60-100m deep by 150mm wide drilled holes, making them a very discreet and compact solution when space saving and minimal ground disruption is a priority.

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Water is an excellent conductor, and this is especially useful when it comes to extracting heat energy from it. Water source heat pumps typically see 5ºC – 6ºC higher return temperatures to the heat pump than other heat sources, further enhancing the efficiency of the heat pump.

Water sources include lakes, ponds, rivers, the sea, and even aquifers, all of which are used very successfully by Kensa to provide heating and hot water to residents on the shoreline (or boat!).

Pond mats are typically utilised to extract the heat from water sources, however methods using boreholes and submerged open loop pipework are also used to great success.

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Heat Networks

Heat networks (also known as district heating) are particularly useful in commercial scale applications, for example in housing developments or business parks.

Kensa has pioneered the development of a system architecture for ground source heat pumps known as ‘micro heat networks’, which attracts an income through the Non-Domestic Renewable Heat Incentive (RHI) for both new build and retrofit applications.

Traditionally rock is utilised as the heat source via borehole collectors for use in heat networks,  however water sources could provide significant groundwork savings and deliver even more efficient results.

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I knew that ground source was a great technology for extracting the natural heat that’s available from the environment to provide a completely green heating system. The good thing about the pipes being in the lake is that water has great conductivity meaning we are able to extract heat sustainably throughout the winter to keep the house perfectly warm.

Mr Clarke, homeowner

Related Content

Blog: The Unbendable Rules of Ground Arrays

Our Technical Director Guy Cashmore has put together some helpful hints about ensuring you get the design and installation of the ground array right.