If you are considering a heat pump as an alternative source of heating for your home then you will likely be aware that ground source heat pumps are one of the main options for property owners. However, ground source heat pumps are not suitable for all properties as factors, such as the space available in your garden or outdoor area, can have a major bearing on whether you will be able to have a ground source heat pump.
Many properties do not have the available space for a ground source heat pump and this is why air source heat pumps are the most common popular heat pump option in the UK. So, how do ground source heat pumps work, what are options, and what are the space requirements for them?
How do ground source heat pumps work?
Simply put, ground source heat pumps extract heat from the ground through the use of a ground loop of water pipes underground. These are laid in trenches or boreholes and extract the heat from the surrounding rock or ground, usually placed at least 1 metre below the ground, where temperatures are a constant 8-10°C all year round.
The ground source heat pump, which runs using electricity, circulates a solution of water and antifreeze around the ground loops and this absorbs the naturally occurring heat.
The water mixture goes through a heat exchanger, or evaporator, where the liquid is heated and compressed and raised to a higher temperature which can then be used to heat radiators, underfloor heating and provide hot water.
Ground source heat pumps require electricity to run, but in general will use far less electrical energy than the heat they produce. The heat pump effectively performs the role that a domestic boiler does in the home.
So how much land or space do you need for a ground source heat pump system?
Ground source heat pumps require a decent amount of space, not only for the ground loop that needs to be installed, but also for the large digging equipment that will need access to the property.
The size of the ground loop depends on the size of your home and how much heat you need. Not all properties are able to accommodate ground source heat pumps because of limited outdoor space.
For some properties, the option of a vertical borehole system provides an alternative when space is limited or ground conditions are less than ideal.
A look at the two main types of ground source system – horizontal ground loop and vertical borehole systems will provide an indication of the space required to install them.
Horizontal ground loop heat pump systems
Horizontal loop systems are the more cost-effective system as they involve the excavation of shallow trenches in which pipes can be laid. However, they do require a larger amount of outdoor space than a vertical borehole system.
Typically, for horizontal ground loops trenches are 100 metres long and 1-2 metres deep. These will hold about 200 metres of pipe which run 100 metres away from the property and 100 metres back. Depending on the size of your home and the heat load it takes will affect how many trenches you need. On average the surface area of land required is roughly 2.5 times the square meterage of the property. Below is an example:
Detached new build property with four bedrooms
Home size = 1582.sq ft x 2.5 = 3,955 sq ft of land required
The trenches are dug with a small excavator, so there has to be enough room for this to enter the site. There are extra factors to think about when working out the amount of land needed, including the number of trees there are and the condition of the ground.
Vertical boreholes systems
Boreholes are normally drilled down to about 100 metres where the ground is a constant 10-12 degrees. This makes vertical systems often more efficient as they are not influenced by the changing seasons. Boreholes are usually chosen due to a lack of space or unsuitable ground conditions for horizontal trenches. A vertical system demands enough space for the drilling rig to enter the site which can be difficult in built up areas, but the boreholes are only 20cm wide.
If several boreholes are needed, these are positioned 5-6 metres apart from each other. The number of boreholes you will need depends on the required heat load for your property (usually the larger the home the more boreholes are needed) and also the type of ground your property is sitting on. Approximately 1 borehole is needed per 6kw, meaning 1 borehole for a small residential home is normally enough. It takes around two days to drill 1 borehole.
Like with the installation of horizontal ground loops, there are aspects which can impact whether boreholes can be drilled close to your home. This is mainly the type of ground that you have, for example green sand and clay are not ideal, whereas rock and wet ground are better conditions. Boreholes are a more expensive method of installation; this is because of the cost of transporting the drilling rig and the specialist team that are needed to operate it.
What is a typical ground source heat pump pipe length?
Ground loops can vary in size but are normally going to be around 200 metres long. As a lot of homes will likely need two or three, with separation between each of them, it is advised that you have around 700-800 square metres to work with.
This can be a considerable amount of space for a homeowner to find, but there are some alternative options. A slinky style setup requires less space because it allows for installation of a length of a pipe in a smaller area but can be less effective because of the loops transmitting heat between each other underground.
Vertical boreholes are another option, but as previously mentioned they can be expensive because of the time intensive drilling process and specialist equipment required.
How deep is a ground source heat pump?
For horizontal loops, the ground will only need to be dug to a depth of 1-2 metres. A vertical loop on the other hand, usually needs to be dug to a minimum of 60 metres but will often be up to 100 metres or more.
Plant rooms required for heat pump systems
If you are planning to get a heat pump installed, you will need to consider where the unit will go. Ground source heat pumps come in a range of different sizes, from those that are small enough to fit inside an airing cupboard or a cupboard underneath the stairs to larger models which could be the size of a washing machine or fridge freezer. The most suitable model of heat pump available to you will depend on the heat output your home requires.
For industrial heat pump systems, it is not uncommon to have two or more heat pumps working together in a cascade style system to provide the heat output that is needed, which would typically involve having a dedicated plant room. In the majority of cases, residential heat pumps are installed in a utility room, garage, or outbuilding. As a recommended space for your heat pump, it would be advisable to have an area that is around 1×3 metres in size.
After installation
Even though the installation process can seem complicated, the result is a highly efficient, easy-to-use system for controlling the temperature of your property. When the system is up and running after professional installation and you have been shown how to use it, there should not be much to do after it has been fitted. There are some simple maintenance checks that should be completed from time to time, and routine services are always a good idea, but for the most part installations work as they should for years.
How can you benefit from a ground source heat pump?
Running costs for a ground source heat pump will be fairly low, which is a big benefit for homeowners once things are set up and used consistently. The cost stays low due to only the compressor needing electric energy. The heat pump is much more efficient than a purely electrical heater would be, which is one of its strongest benefits.
As well as low running costs, you can get a heat pump grant to reduce the upfront cost of the unit.
Another benefit is that a ground source heat pump can work for cooling and heating needs. With other types of systems, a separate air conditioner and boiler would be needed. For a heat pump to work for both, the valve simply needs to be reversed to change the direction of the circulating fluid.
Lastly, the value of a home can increase with a properly installed GSHP. Since the installation is the main cost, having one already fitted and running will be an advantage if and when it comes to selling your property.
