Guidance on installing ground arrays.

Full details are available in the Installation Manuals supplied with the product. It is important that the manual is read before any installation begins.

Ground arrays are a critical part of any heat pump system and it is vitally important that these are sized and installed correctly. Incorrectly sized or installed ground arrays can result in higher heating bills and ultimately the ground can run out of energy during the heating season, leaving the building and occupants cold.

There are a number of ways of installing ground arrays and Kensa would generally recommend installing ground arrays using the slinky method. The invention of the slinky in 1985 is credited to Oklahoma University in the USA, which could be considered the heart of ground source heat pump technology.

Slinkies are considered by many ground array design experts to be the best method of “horizontal ground coupling” for heat pumps. Every one meter of slinky is roughly equivalent to 5m of slinky pipe.

They are particularly well suited to the UK, and require less digging per kW of heat delivered than any other method and therefore offer the most economic installation costs.

If installed and sized correctly they offer the same performance as straight pipe and will not overcool the ground any more than straight pipe.

The amount of ground required for the ground arrays depends on the heat demand for the house, which in turn depends on the insulation levels, size of the building and temperatures required. The lower the heat demand the less ground required. As a rough rule of thumb, every 10m of slinky will provide 1kW of heat. Kensa slinkies are available for 30m, 40m or 50m trenches, the 30m uses 200m of MDPE pipe (32mm OD), the 40m uses 250m of pipe and the 50m uses 300m of pipe.

Each slinky has a 20m header to enable the flow and return to be connected to the slinky manifold at the building. It is important to keep all slinkies to the same length, this equalises the pressure drops within each slinky and means equal flow around each slinky.

Slinkies can be installed in two ways and the easiest way will depend on the site. To reduce the amount of digging, placing the slinkies on their edge within a 2m deep trench is generally preferred. The trenches need to be 2m deep (so the top of the slinky is 1m below the surface of the ground) but only 300-400mm wide, i.e. the narrowest digger bucket. If more than one slinky trench is required then each trench needs to be separated by 5m between centres. (This is for the coiled section of the slinky only).

The bottom of the trench should be covered with a layer of sand and if the ground is heavy clay or contains sharp stones, we would recommend that the slinky is completely covered in sand before the excavated ground is placed on top.

If ground conditions mean that a trench 2m deep cannot be dug, then it is possible to place the slinkies flat within a trench that is 1.2m deep by 1.2m wide. This would also reduce the amount of sand required to cover the slinky if ground conditions require this. Trenches would still need to be separated by 5m between centres and so there is no overall increase or decrease in required area.

It is possible to change between a narrow or wide trench at anytime.

Straight pipe ground arrays are also possible and Kensa can supply these if required. Please contact Kensa for further information.

For further information on installing Slinky ground arrays please click here.

Kensa can also fully advise on using other heat sources such as lakes, boreholes or rivers. Please contact Kensa for further information and guidance.

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