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Many of us are working towards reducing our energy consumption, for a variety of reasons, and heating our homes and our water accounts for 78.4% of our energy use. So focusing on ways to make your heating system more energy efficient is one of the most powerful ways for you to reduce your energy bills and your carbon emissions. A ground source heat pump is a popular and effective method of reducing energy consumption, but how does it work? Let’s take a look.
A ground source heat pump uses a method of extracting heat from the external ground and transferring that heat into a property’s heating and hot water system. It works the same way as a fridge but in reverse. A fridge transfers heat from the inside to the outside, whereas a ground source heat pump transfers heat from the outside to the inside.
The mechanics can be reversed to work identically to a fridge, and this allows for the use of a ground source heat pump for cooling a building as well as heating it.
Take a look: How Much Does It Cost To Install Ground Source Heat Pump
A ground source heat pump absorbs heat from the ground. Even in cold weather, the outside ground keeps a relatively stable temperature. In the UK, this is usually between 7 and 13 degrees Celsius. Ground source heat pumps extract this heat and use it to heat a building and its hot water system.
To absorb heat from the ground, a network of pipes is needed. These are placed underground and are known as a ground loop circuit or a ground array.
A liquid mix of water and antifreeze (thermal transfer fluid) constantly circulates through these pipes. Using the theory that heat moves from warmer to cooler spaces, this constant circulation of cold liquid attracts heat from the surrounding ground.
There is a heat pump located inside the building. Within the heat pump is a refrigerant liquid, similar to what you would find in your fridge. The heated fluid from the underground pipework enters the heat pump, where a heat exchanger transfers the heat to the liquid refrigerant.
The refrigerant liquid is now carrying the heat from the ground outside, and here the temperature is raised even further. This is achieved through the use of a compressor, which compresses the liquid and raises the temperature significantly.
The refrigerant liquid is now hot enough to boil and turn into a gas.
The refrigerant gases are passed through another heat exchanger, which transfers the heat into the building’s hot water and heating system.
In many cases, the ground source heat pump system can be incorporated into the existing heating system, hot water system, or underfloor heating system. Some systems, especially older ones, may need some modifications to incorporate the ground source heat pump.
The thermal transfer fluid now returns to the ground loop circuit to pick up more ground heat and begin the cycle again.
There are a variety of ground source heat pump types available, some of which address potential issues with space.
This type works on the same principle as ground source heat pumps. They transfer outside heat to indoor heat using a refrigeration heat pump system. Instead of taking that heat from the ground, however, they take it from the outside air.
Air-source heat pumps save space compared to ground-source heat pumps and they are less expensive to install. This is because they only require the installation of the heat pump unit, rather than underground pipework.
They are less efficient than ground source heat pumps, however. This is partially because outside air temperature is much less stable than ground temperature. So only colder days and at night, the heat pump will need to use more energy to extract heat from the air.
An air source heat pump can be more effective at cooling a building because they are air conditioners, although ground source heat pumps can also perform this function.
Explore further: How Does An Air Source Heat Pump Work
Closed loop systems are the most common type of ground source heat pump, but they can come in a variety of forms. They are so named because the pipe circuit is closed, meaning that the thermal transfer fluid keeps circulating through the same system.
A horizontal closed loop ground source heat pump system involves laying the ground loop in horizontal trenches. These are usually placed 4-6 feet underground but will need a relatively large amount of land to be able to lay enough pipework.
For a standard residential three-tonne system, you would need around 1,200 to 1,800 feet of trenches in total. To fit all of this in, there will need to be between 1/4 and 1/2 acres of available land.
Horizontal closed loop systems are cheaper to install than other options because they don’t require any drilling, but they do require a large amount of land, which isn’t always an option.
A vertical closed loop system is the solution to not having enough available land space for a horizontal system. Instead of digging a network of narrow trenches, you would drill vertical boreholes into the ground between 100 and 400 feet deep.
Compared to a horizontal system, a vertical one requires much less land. For a standard three-tonne residential system, you would need a total of 450 to 900 feet of borehole length, and this would take up a fraction of an acre.
Vertical closed-loop systems are more expensive to install because of the extensive drilling required, but they are more versatile and can be installed in properties with much less available land.
A water-source system extracts heat energy from a nearby water source, rather than the ground itself. The pipes are submerged in a pond, lake, or other body of water.
Otherwise, the system works the same way. The water in the pipes is heated by the heat present in the external water, and then taken to the heat pump to be transferred into the property’s heating and hot water system.
This system is cheaper to install than other options, but it can be used in limited situations. There has to be a close enough body of water, and the water needs to meet certain criteria for it to be usable.
An open-loop system is less commonly used than a closed-loop system. The underlying mechanism is the same as a closed-loop ground source heat pump, with the main difference being the water used to take heat to the heat pump.
Rather than inserting a water/antifreeze mix into the underground pipes, an open-loop system draws the water from groundwater, wells, lakes, rivers, or other surface water sources.
Water is drawn from this surface water into pipes and is taken directly to the heat exchanger. Here, it is used to heat the liquid refrigerant, which is then compressed, and the heat energy is used to heat the building.
Once the surface water has been passed through the heat exchanger, it is taken back outside and discharged. More water is then taken in from the water source, and the cycle starts again.
This is an open loop system because the same water isn’t cycled through each time. The water from one cycle is discharged while new water is taken in.
An open-loop system can be cheaper to install and is typically more efficient than a closed-loop system. Groundwater tends to keep a stable temperature so it requires less energy to heat the refrigerant.
There are tight regulations, however, around how the water is discharged, and the system will need a fair amount of maintenance. Because it is an open system that uses natural water, there is a chance of contamination and blockages.
A hybrid ground source heat pump system combines different types of heating methods to create the most efficient system.
There are a variety of hybrid systems available, including:
These types of systems are often used in buildings that require a large amount of energy because they maximise the available heat energy. The method used can be altered in real time to ensure a constant supply of heat at the best efficiency possible.
They can also be useful in areas where there is a large amount of variability in the outside temperature.
If you are thinking of installing a ground source heat pump, we can help. At Heat Pump Heroes, we have the training, knowledge, and experience to install effective and long-lasting heat pump systems that work for all property types.
When you book a consultation with us, our team will conduct an on-site consultation to assess your existing heating system, the available outdoor space, and the potential for water sources.
We will then discuss with you the best options for you, and develop a convenient installation plan. Our ongoing support will ensure that you are kept up to date with the project’s progress every step of the way.
Contact us today to start your ground source heat pump journey.
Ground source heat pumps utilise naturally occurring heat stored in the ground to heat both a central heating system and a hot water system. Heat pumps are incredibly efficient, and will use far less energy than gas boilers and direct electric heating systems. There are versatile options available that take into account space and environmental constraints. Heat pump installation falls within the budget of most residential projects, especially with available government grants, and will save money on energy bills long-term.
