How Ground Source Heat Pump Systems Work
Are you new to Ground Source Heating and Cooling?
You’ve come to the right place!
How a heat pump works
Let us introduce you to one of our favourite customers: Kensa Heat Pumps. Kensa are UK manufacturers of ground source heat pumps with their factory in Truro, Cornwall. They have three aspects to their company, Kensa Heat Pumps (Manufacturing), Kensa Contracting (Heat Pump Installations) and Kensa Utilities (Infrastructure.) They created the video below which perfectly describes how a heat pump works. We are a design partner for Kensa and are responsible for the majority of the designs for their installed systems.
Types of Ground Source System
A well designed Ground Source Heat Pump System always starts with the building.
What type of building is it? What are the peak heating and / or cooling loads? What are the annual loads (hourly loads are best)? What is it’s location and full post code?
The next stage is to look for available energy sources. Ground Source Heat Pumps harvest energy (mainly from solar gains in the UK) from the ground in heating mode and transfer heat back to the ground in cooling mode. When we investigate below approximately 3m depth we measure something called the undisturbed ground temperature which ranges from between 8 and 12 degrees Celsius in the UK.
At Genius Energy Lab we use our 20 years experience and specialist in-house and prioriatery software to model the ground based on the requirements of the building which results in the design and specification of an energy collector. Each type is explained below.
Ground Source Heat Pump systems can broadly be categorised into three types of system before further breaking down the technology dependant on the available resources at the site. These three types are called Closed Loop, Open Loop and Hybrid systems and are further explained below.
Closed Loop Systems
Closed loop systems can be vertical, horizontal or involve heat exchangers submerged in bodies of water. The key thing is that all the fluids run in a closed system of pipework.
The illustration here shows a high rise building connected to a ground array consisting of 12 boreholes which typically range from between 80 to 300m deep.
Each hole is 150mm in diameter and contains a loop of Polyethylene pipe and once installed the holes are backfilled with a cementitious thermally conductive grout.
The pipes contain an antifreeze liquid which enters the ground at a temperature of 0-5 degrees. None of this liquid ever comes into contact with the ground as the system is closed loop.
Because the ground temperature is typically between 8 and 12 degrees Celsius year round, heat moves from the ground into the liquid in the pipes. The heat picked up from the ground enters the heat pump and via a compression cycle is converted into more useable heat at a higher temperature. This can then be used for heating and hot water.
Heat pumps can also work in reverse whereby heat is collected from a space in the building and returned to the ground in cooling mode.
The heat pump runs on electricity and for each unit of energy used to run the heat pump, 3 to 6 units of heat are delivered to the building meaning that they are 300% to 600% efficient, compared to a traditional gas boiler which is approximately 80% efficient.
Another way you may hear the efficiencies of heat pumps outlined is via a term called Coefficient of Performance or COP. For the above example the COP would be 3 to 6 and it represents the energy output divided by the energy input. It is very important when considering COP to look at the seasonal COP (the average over the year) and Genius Energy Lab can assist in heat pump selection and sizing to achieve the best COP’s for your system. The COP in cooling mode can be up to 7 or 8.
Open Loop Systems
Following an analysis of the geology at a site it may be that we identify the presence (or potential presence) of an aquifer (underground water).
Open loop systems typically consist of a pair of water wells connected back to the building via pipework.
Water is abstracted from well 1 (the extraction well) at the temperature of the ground. Heat is harvested from this water at the heat pump, before the water is then returned to the aquifer in well 2 (the injection well). As described above the heat pump uses a compression cycle to move this heat from a cold place to a hotter place and used for heating and / or hot water.
The systems are termed Non-consumptive, because the net effect is that no water is removed from the aquifer. Work is required with the Environment Agency (EA) to license a system such as this and the process can take up to a year.
These systems are extremely efficient and can be used for heating and cooling.
Hybrid Systems
Hybrid systems can consist of a combination of closed loop and open loop systems as well as combining ground source heating and cooling systems with several other technologies such as solar thermal, combined heat and power (CHP) and photovoltaic thermal (PVT) panels.
The diagram here depicts combining a closed loop borehole with solar thermal.
Hybrid systems are an interesting area of ground source heat pump system design and Genius Energy Lab have vast experience in this area.
Each project is different and we will ensure that you get the best and most up to date advice to ensure the success and cost effectiveness of your project.