“How much space do you need for a ground source heat pump with loops?”
This is a question that comes up a lot when speaking with my clients in Hampshire, Berkshire, Surrey and beyond. It’s critically important that you have sufficient space in which to install the pipework for a ground source heat pump. Before we talk about land, here’s a brief summary of how a ground source heat pump works:
How do ground source heat pumps work?
Ground source heat pumps use loops of pipe beneath the ground, these are either laid in trenches or placed in boreholes. Around 1 metre below the ground there are stable temperatures of around 8-10°C all year round. The pipes below the ground contain a brine mixture of water and antifreeze. As this mixture moves around the loop, it extracts heat from the surrounding ground.
This low temperature heat is transported to the heat pump unit. Here in the heat exchanger, also known as an evaporator, the brine meets the ice-cold refrigerant which is then heated by a few degrees and evaporates.
This is transferred to a compressor which raises the pressure of the refrigerant, which in turn further raises its temperature. This heat is transferred by the heat exchanger (condenser) to the heating system where it is used to heat radiators or underfloor heating and domestic hot water.
Meanwhile, in the heat pump, the refrigerant reverts from a gas to a liquid and passes through an expansion valve to lower the pressure and reduce the temperature. This is then cycled back through the system.
So, how much land do you need?
While there are of course other factors to consider when sizing a system, it’s fair to suggest that as a guide, an 8kW Thermia ground source system would require around three ground loops, each at 200 metres in length. A minimum land area of 700 square metres would be necessary for loops of this size to be laid.
In order to visualise how the ground loops are laid within this space, imagine that each loop is laid as a rectangle with 1 metre of separation – the rectangle formed by the loops would be 7 metres in width by 100 metres in length.
The image below demonstrates how three 250 metre ground loops have been laid.
How does geology affect installation cost?
Different soil and rock types provide variable energy volumes. For example, if the soil is wetter, the requirement might be for only two 200 metre ground loops; one less than if the soil is of a drier consistency. This would then reduce the ground work trenching costs. This is because energy transfers better though water.
What about the trenches?
There are two methods for digging trenches for ground loops; both have pros and cons but ultimately it will be down to you or your ground workers to decide which option is best for you.
Narrow trenches require less digging and can be achieved with a small digger bucket, but it can be harder to lay the pipe with less space.
Wide trenches require a lot more digging and can be more costly, but laying the pipe should be an easier process with more space to work with.
What if there isn’t enough space?
If there is insufficient land for horizontal ground loops, you can consider “slinkies”. Whilst they can be less efficient than ground loops they require less space. Alternatively, you can consider vertical boreholes. However, this can add significant cost to your project depending on local geology. We find that many of our customers will at this point consider an air source heat pump; a viable and efficient solution with lower capital investment.
Call 0800 865 4328 today and ask one of our experts about the best heat pump solution for you.