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.

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 ground array 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. Only MDPE or HDPE (Medium or High Density Polyethylene) pipe should be used, with at least the PE80 pressure rating. Blue pipe denotes that the pipe contains only fresh water under Water Resources Council guidelines and hence should not be used, as ground arrays contain antifreeze.

Each slinky has a 20m header to enable the flow and return to be connected to the slinky manifold at the building. This allows the 2 m deep slinky trench to be terminated a little way from the building and for the header pipes from all the slinkies to join together into a single header trench, which is often only 1.2 m deep. This allows the header pipes to exit the soil vertically, directly under the Slinky Manifold, which is always fixed to the outside of the building.

For distances were the header pipe is too short, it is possible to uncoil a loop from the coiled section and use this for the extra distance. However if one loop is uncoiled at the front of the slinky a second loop must be uncoiled from the end of the slinky to provide enough pipe for the added distance for the return. These uncoiled sections must also be a minimum distance of 1 metre apart from other slinkies,

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).

Click here to watch a movie of a slinky trench being dug.

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.

Placing the slinkies in the trench.

The ideal method is to turn the packed slinky coil on it's edge and carefully unroll the slinky next to the trench, allowing each individual loop to drop onto the ground next to the trench. At the end of the trench (after all the loops have been unrolled, unroll the remaining pipe (return pipe) back along the trench to the start.

Cable tie the return pipe to the final loop where the pipe turns back on itself and to the bottom of all the loops to provide the slinky with more rigidity.

Carefully place the slinky in the trench.

The Return

The return pipe should be in the same trench as the slinky, and run up the side of the building and into the slinky manifold.

Unused or excess pipe

Allow enough pipe above ground (usually 1.5 metres) to cut down and connect into the slinky manifold, any excess header pipe can be coiled back into the header trench.

Alternatively, it can be cut off, as long as the same amount is cut off all the slinkies

For further information on installing Slinky ground arrays please download the Kensa Slinky Guide.

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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