Content supplied by Kensa Heat Pumps
Ground arrays for ground source heat pumps can take many different forms, but the two most commonly used in the UK are vertical drilled boreholes with a U tube of pipe in them and looped horizontal pipe, usually called slinkies.
Both have advantages and disadvantages, see table below:
|Smaller land areas can usually meet the heat load, as depth of the borehole can be varied.||Requires specialist drillers which usually works out expensive, especially on smaller jobs.|
|Can be installed in virtually anywhere and situated under car parks or buildings.||Getting physical access for a drill rig can sometimes be challenging.|
|Usually cheap and easy to install.||Sufficient land area is needed to collect and deliver enough energy.|
|Trenching work can easily be done by a digger that is already on site.||Need to go into topsoil and are affected by what’s on top of them.|
An accurate heat loss calculation for the building is absolutely essential when designing any ground array – get this part wrong and everything else about the system will likely be wrong, too!
It is also worth noting that the water temperature that the heating distribution system runs at changes the efficiency of the heat pump.
Heat pump efficiency also has an effect; one of the ironies of using an ultra-efficient heat pump like the new Kensa Evo is that the ground array size needs to increase slightly.
Here are some other top tips to consider:
Make the best of what you’ve got
In the case of the exposed land area not being large enough to meet the heat demand, investing in insulation and other measures can help reduce the load. This often means that the available land may well become viable as the heat source, allowing slinkies to be used thus avoiding the higher installation costs associated with boreholes.
Ground arrays don’t have to follow the usual ‘one heat pump one array’ route – they can be shared between multiple properties in a similar fashion to district heating. Each property has its own heat pump, so doesn’t require any metering or billing arrangements. The boreholes or slinkies can also be sited wherever practical, rather than individually in gardens. Unlike the ‘one heat pump one array’ route which qualifies for 7 years of payments through the ‘Domestic Renewable Heat Incentive (RHI)’, a district configuration qualifies for the ‘Non Domestic RHI’, which is payable over 20 years.
Other sources of free energy can sometimes be found, such as existing water wells, old mines, natural springs, river water and even sea water. Water is an excellent conductor and makes a highly efficient, low cost energy source for a ground source heat pump.
Case study: Wanstead, Eco House
This Kensa project proves that even in the city, with limited space, you can have your own green haven!
Architect Jason Harris was looking for a renewable heating system to complement an innovative eco home he was building in East London.
Land area was restricted due to the urban nature of the site, but thanks to a unique horizontal borehole drilling method, a Kensa 20kW twin compact ground source heat pump was successfully installed.
- 550m² new-build eco home;
- Kensa 20kW Twin Compact ground source heat pump;
- Underfloor heating and polished concrete floors;
- Solar thermal providing additional hot water;
- Heat recovery ventilation system;
- Low consumption LED lighting and appliances;
- Eligible for Domestic Renewable Heat Incentive RHI.
The heat pump has been running for over a year and the owners are very happy with how it is performing.
The case study and pictures can be viewed at https://www.kensaheatpumps.com/wanstead-east-london/