Ground source heat pumps (GSHP) is a renewable energy source with heat is extracted from the ground for homes and or commercial buildings.
This natural heat source can reduce energy bills by up to 50% compared to a conventional heating system. But how do they work? And why should you consider ground source heat pumps?
In this article, we take a deep dive into the technology, the costs, the advantages and disadvantages to help you make an informed decision about buying or designing a GSHP.
What is a Ground Source Heat Pump (GSHP)?
A ground source heat pump extracts heat energy from below the surface of the Earth. By circulating a fluid (usually water and antifreeze) through underground pipes, high ground temperatures heat the fluid within the pipe, which is pumped back up to be used for heating or cooling in a building.
See here for more details:
A geothermal heat pump should not be confused with geothermal energy, which uses a high-temperature underground heat source to generate electricity.
Compared to conventional heating systems, ground source heat pumps can save you up to 50% on heating bills, but require an upfront investment for installation. We will discuss the cost implications of a GSHP installation later in this article.
Across the United States, heat pumps are widely used but less so in the United Kingdom, but this is changing with several incentive schemes being rolled out to increase intake.
Powering your building heating system with a ground source heat pump
A ground source heat pump is a ground-based heating and cooling system which uses the Earth as a heat source in the winter and a heat sink in the summer (in the United States, usage in other geographies will vary).
It works by extracting heat from the ground, which is much more stable than the air temperature above. In fact, the ground is the largest solar collector on the Earth, naturally absorbing the Sun's heat during the day and releasing it at night - think of the difference between sitting on a hot pavement and a grassy field.
The heat pump then transfers this warmth into the air inside your home via underfloor heating or conventional radiators (see section below on Space Heating).
How much does a Ground Source Heat Pump cost?
The average cost of a ground source heat pump depends on several factors, including the size of the house and whether it is a new or an existing home, and ease of installation (more on the installation process below).
Typically, you'll be likely spend between the range of $8,000 and $20,000, on average, in the United States, and between £10,000 to £18,000. This depends on the size of the system and does not include the cost of fitting underfloor heating if required). This figure is from the Energy Saving Trust.
Increasingly, in many countries, grants are available for the installation of Ground Source Heat Pumps.
What grants are available for Ground Source Heat Pumps installation?
In the UK, you can apply for a Domestic Renewable Heat Incentive (RHI) grant to cover some of the costs - visit the UK Government's advice page for more details. The amount you may claim depends on a variety of factors (for example, your income), but it's best to check the latest update of the scheme for full details.
Is my house or building suitable for a Ground Source Heat Pump?
GSHPs are the most energy-efficient way to heat your home, and the UK Government is currently offering grants for installing them. But, not all houses make for suitable candidates for a GSHP installation (most, but not all).
The primary requirement is that you have access to some outdoor space near your home for the heat pump installation. This can be a field, a piece of ground behind your house, or a driveway. It doesn't have to be that big, but it does have to be open, flat, and outside.
We must emphasize you don't need a large space; a good contractor will tailor the design of your system to the space you have available.
Ground Loop Installation
As you can probably guess, the ground loop is the long pipe through which your mixture of water and antifreeze is pumped. The layout can depend on your garden size and shape. The contractor will make the correct assessment and choice between horizontal collectors, compact horizontal or vertical collectors, o r vertical borehole collectors. Each of these methods of installation is explained in more detail in this (slightly dated) video.
Your local heat pump installer (contractor) will be able to provide advice about whether you need a Closed Loop or a Horizontal Loop system.
Space heating via underfloor heating or radiators
Another important factor to consider is the method of heating your house currently uses inside your home.
The heat output of the water from a typical GSHPs system is within the range of 35 - 45 degrees Celsius. This is ideal for an underfloor heating system, which have a lower heat requirement, but if your house has conventional radiators, you will have to:
use more energy to heat the water up to around 65 deg. C. which is required for radiators,
or be happy with cooler than normal radiators. One option is to trade your traditional radiators for larger surface area radiators that operate at a lower temperature.
These temperatures quoted can vary. A heat pump's maximum output temperature depends on several factors, including how fast the water flows through the residential hot water cylinder and the temperature of the ground.
Savings on your carbon footprint with ground source heat pump vs. non-renewable fuels (gas heating)
A typical Ground Source Heat Pump uses a mere 31-42% (depending on the efficiency of your GSHP system) of the carbon emissions you could expect from an 85% efficient gas boiler.
GSHPs also produce a much lower carbon footprint when compared to Coal Heating, an Oil Boiler, and Direct Electric Heating.
The energy requirement for GSHP comes from the electricity required to pump the energy through the system. However, the carbon content of this electricity will continue to decrease over time as grid electricity as more of the electricity grid is powered from renewable sources. Furthermore, heat pump efficiency is also expected to improve in the coming years.
Difference between a ground source and air source heat pump
Both ground source and air source heat pumps come from the same family of energy efficiency measures. In both methods, a heat pump exchanges thermal energy from a heat source (e.g., the ground, the air, or even water) to a building. One advantage of the ground source heat pump is that the ground temperature is often higher than the external air temperature (and more stable). This temperature difference (between the ground and the temperature of the body of water being pumped through the system),
Five advantages of a Ground Source Heat Pump System
- Ground source heat pumps offer an extremely efficient energy source for space heating or cooling in your home. The relatively constant temperature of the ground means heating in winter can consistently be provided by your GSHP. This is an advantage over other sustainable energy sources such as solar energy.
- Although the heat pump installation process can be difficult and costly, you benefit from a very low emission and low maintenance source of energy once installed.
- In time, the installation cost will only go down across the world, with governments beginning to incentivize their installation
- Unlike gas boilers, ground source heat pumps do not emit any particulates - especially Nitrogen Oxide and Sulphur Oxide.
- GSHPs are often called invisible heating systems, as they are silent, low maintenance, and generally out of sight. Apparently, planning authorities look favorably upon them too, in the UK at least!
Advice and next steps
If you are looking to find out more information about ground source heat pumps, we recommend as a next step to talk to a local contractor in your area. If you are in the UK, the GSHP Association website is a great place to start as it provides a full list of accredited companies and a wealth of further information about GSHP.
Shifting away from fossil fuels must be a priority for us all over the coming months and years. Installing renewable technologies such as the ground heat exchanger is just one step to reducing the amount of energy your house uses for space heating or cooling.
It should be used in combination with an insulation strategy to minimize heat loss. In doing so, you will see drastic cuts to your fuel bills as well as your carbon dioxide emissions.