Geothermal heat pumps: The ultimate guide to ground-source heat pumps
This guide offers a detailed overview of ground-source heat pumps. We have also put together a separate guide for water-source heat pumps and an overview of the two geothermal heat pump types.
What is a ground-source heat pump?
Ground-source heat pumps are a type of geothermal heat pump that use the ground as a heat source and heat sink. The soil beneath the ground surface is always warmer than the air above it in the winter and always cooler than the air during the summer.
Ground-source heat pumps can be more complicated to install than other heat pump types, as they require groundwork to install the collector. However, ground-source heat pumps offer unique and significant advantages to owners. Let’s take a closer look at this geothermal heating and cooling heat pump technology.
How does a ground source heat pump work?
Ground-source heat pumps work using the same principles of the refrigeration cycle that apply to all heat pumps. Instead of using air as a heat source, though, they extract heat from the ground.
Essentially, the ground-source heat pump uses an underground pipe to capture heat energy stored in the ground. This pipe can either be placed horizontally in a series of loops or as a straight vertical line going deep beneath the surface of the ground. We’ll take a more detailed look at these options further down.
A detailed explanation on the refrigeration cycle is available in our article on how heat pumps work.
What are the different types of Ground-Source Heat Pumps (GSHPs)?
Ground source heat pumps typically fit into one of two broad categories: residential GSHPs and commercial GSHPs.
The distinction is mostly based on heating capacity and feature sets rather than any major technological difference.
Residential GSHPs are mostly designed for residential use or small commercial applications. Commercial GSHPs on the other hand, offer larger heating capacities and advanced features for industrial or commercial use such as waste heat capture and recycling, modular scalability and so on.
The TermoPlus TerraPump range is mostly suited to residential and small commercial use whereas the TermoPlus TerraPump Pro is our industrial / commercial heat pump range.
What can a ground-source heat pump do?
Residential ground-source heat pumps can provide heating during the winter and cooling during the summer if they are reversible. Many models can also provide sanitary hot water heating (domestic hot water / DHW) too, while others may allow for heating swimming pools. They can also be fully powered by solar panels and battery storage (or solar PV net metering), which could make them a true net-zero heating and cooling solution.
Commercial ground-source heat pumps can typically do everything a residential GSHP can do with additional benefits. Industrial / commercial GSHPs can capture waste heat from industrial processes (increasing efficiency even further), they can often provide ventilation and humidity control as part of a larger HVAC solution and they may also be able to provide space cooling for applications such as cool storage or small server rooms at no additional energy cost when heating other spaces. Check out our detailed article on industrial / commercial heat pumps to find out more about the benefits and applications of a commercial ground-source heat pump.
What are the benefits of ground source heat pumps?
What benefits does a ground-source heat pump offer? Why should you choose a ground-source heat pump instead of an air-source or water-source heat pump? Let’s take a quick look at the benefits of geothermal heat pump systems, GSHPs in specific, to see why they are considered the top tier choice for heat pumps.
Energy-Efficiency, Thermal Performance and Long-term returns
The potential for energy savings is massive for GSHPs.
Our GSHP units can typically reach a COP of 6.0 and some even a COP of 10.0 when heating and cooling are simultaneously used. Ground-source heat pumps rank at the very top for energy efficiency for all heating and cooling systems and other heat pump types. Their consistent access to a steady heat source not only offers extremely high energy efficiency, but also a certain level of stability not typical for air or water-source heat pumps.
Although GSHPs may cost more and are more complex to install, their higher savings compound over their very long lifespan and provide an exceptional financial return.
Comfort levels
Air-to-air heat pumps, air conditioning units and ventilation-based heating systems (ducted heating) push warm air into spaces to heat them. This does not typically provide the same level of comfort as radiators or underfloor heating. When ground-source heat pumps use radiators of underfloor heating they can provide a better heating experience for the inhabitants while also remaining exceptionally energy-efficient. With high capacities and their lower cost of operation they can provide abundant warmth and unparalleled comfort without the stress of expensive heating bills.
Cooling in the summer
Depending on the installation design, reversible ground-source heat pumps can also provide cooling during the summer, negating the need for additional air conditioner units. Some systems can produce cooling and sanitary hot water at the same time with the same amount of energy.
Low Noise Levels
Air-source heat pumps in particular have in the past caused concerns in the past as their external units could be quite noisy in some cases, causing distress to homeowners and their neighbors.
All heat pumps have had significant advances in noise reduction over the last decade or so. All geothermal units are exceptionally quiet and don’t require an external unit, so there is absolutely no concern for meeting local guidelines regarding noise levels at all.
Resilience in Extremely Cold Weather
Although great strides have been made in air-source heat pump technology to allow for heat pumps to operate in extreme temperatures as low as -25°C, no other heat pump can offer the dependability in harsh conditions that a ground-source heat pump can offer.
With very stable ground temperatures, especially in the case of vertical ground collectors, ground-source heat pumps can offer a reliable source of clean and highly efficient heating during harsh winters.
Stability
The advantage of using the ground as a heat source is that it is much more stable compared to sources such as the air or water sources. There is no volatility and the almost constant ground temperature provides a steady, dependable source of heat in the winter and cold in the summer. This is particularly the case with vertical collector GSHP installations.
Increased property value
Having installed a ground-source heat pump in your property will likely increase its value as new owners will have the benefit of a highly efficient heating system infrastructure without having to endure the inconvenience and cost of having it installed. Both horizontal and vertical ground collectors can last up to 50 years (or more with newer products) which may allow them to serve a replacement heat pump in the future.
Typical Ground-source Heat Pump applications
GSHPs are not as widespread as air-source heat pumps, mostly because not all sites are suitable for the installation of GSHP collectors. Retrofits are not often practical and sometimes even new builds can be challenging. Communal buildings such as multi-storey flats, highly urbanized locations and unsuitable soil conditions, are not ideal sites for ground-source heat pumps. The higher initial cost of GSHPs is another factor to consider.
However, GSHPs are ideal when the site allows for them and the goal of the system is to maximise energy efficiency over the long-run. They are especially suited to situations where greater heating capacities are needed, or when there is an abundant source of heat to tap into, such as industrial heat-generating applications.
Sometimes GSHPs are the only realistic heat pump alternative if the site is located in an extremely cold climate and dependability is crucial.
GSHPs are the top-tier option for high energy-efficient heating in residential applications. They are also frequently used in commercial settings, including community and district heating. Hospitality is another sector that often uses GSHPs for central heating or even for multiple buildings such as multiple individual rentals closely situated. Industrial and commercial heating and cooling applications are plentiful for GSHPs which can offer unique advantages such as heat capture and recycling.
How are ground-source heat pumps installed?
Ground-source heat pumps are always closed loop systems. That means, the refrigerant or water mix is sealed in the ground collector and recycled through the system without getting in contact with the ground or any water bodies.
Ground heat exchangers can typically use either horizontal ground collectors or vertical collectors (through borehole drilling). We’ll get back to this but let’s take a look at some important site factors first.
Important site factors for ground-source heat pump installations
Installing a geothermal heat pump, whether ground-source or water-source always requires thorough site analysis and planning.
The geological characteristics and thermal properties of the ground can play a significant role in the feasibility and performance of a ground-source heat pump, especially for horizontal installations.
The higher the thermal conductivity of the soil, the easier heat transfer will occur. Loose, sandy, rocky or loamy soil can allow for better heat exchange compared to clay, compacted or silt soil. Groundwater saturation can also improve the thermal transfer properties of the soil. Permafrost in extremely cold climates can pose problems.
Sites with slopes may allow for the collectors to be installed at a greater depth, taking advantage of more stable temperatures. Let’s now take a look at the ground loop or vertical heat exchanger options for ground-source geothermal systems.
Horizontal installations
The ground collector can be buried in the ground below a garden or space that won’t have a structure above it.
A horizontal installation involves the excavation of the ground to a depth typically between 1.1-1.3m. At this depth it is expected that there will be more seasonal variation of the soil temperatures (7°-15°).
The ground collector, which is typically made of high-density polyethylene (HDPE), is buried in the ground forming a series of horizontal loops through which typically a water-based mix (usually a propylene-glycol (PG) water mix) will circulate. The mixture is non-toxic so there is no risk of contaminating the ground with toxins, while at the same time it has antifreeze properties so that the fluid never freezes up.
In the past some systems used to use refrigerant in the ground collectors but that is less common nowadays due to environmental concerns. There are also other less common alternatives to PG-water mix such as salt-based brines, ethylene glycol or Thermox DTX which have different advantages and disadvantages and can be specified by your installer if the situation requires it due to specific site factors.
This type of installation requires more available space than a vertical installation but is also likely to require fewer permits from local or national authorities, depending on your location. A practical disadvantage of the horizontal installation is that the land above the installation cannot be used for construction, but only for landscaping.
Vertical installations
A vertical installation involves drilling boreholes vertically into the ground at depths typically between 60-140m. At this depth the temperature is stable all-year round (~12°), reducing seasonal variation.
This type of installation requires less space compared to a horizontal installation but may more regulated in terms of permitting by local or national authorities, depending on your location.
One of the major advantages of a vertical installation is that once completed, paving or buildings can be placed above the collector.
Just as with horizontal GSHP systems, they also typically use HDPE pipes with a PG-water mix to transfer heat to the heat pump.
How to choose the right Ground-Source Heat Pump System for your needs
The choice of a GSHP is usually due to an emphasis on high long-term energy-efficiency and high comfort standards. This means you will need to compare the coefficient of performance (COP) or Energy star ratings of the units you are considering.
Matching your requirements to the system’s capacity is crucial to achieve a high energy efficiency. Correct system sizing and heating system capacity selection will play an important role in reaching a high COP in practical terms.
Since GSHPs carry a higher initial cost, it is recommended that you choose a brand that has a long history producing high quality, dependable ground-source heat pumps. That is because you want to prolong the financial savings offered by the system over as many years as possible.
Correct heat pump sizing has a major impact on energy efficiency. Since your needs may change over time, it is useful to have a heat pump that can increase or decrease heating capacity without sacrificing energy efficiency. Options such as cascading and multi-stage operation mean heat pumps can be scaled upwards in this way.
The most flexible solution with the highest efficiency gains that can optimize efficiency on a daily basis is the inverter-driven ground-source heat pump. We are currently developing the TermoPlus GeoPump inverter-driven GSHP series which offers unparalleled energy efficiency through the use of inverter technology.
If you live in a climate were cooling is necessary during the summer, it is probably a good idea to pick a reversible GSHP that can offer you cooling as well as heating.
Finally, making a choice on such a technical decision is a bit easier if you get input from heat pump installers that visit your site and give you the facts you need to take into consideration.
Frequently asked questions about Ground Source Heat Pumps:
What are the downsides of a ground source heat pump?
There are certain cons that may make a ground-source heat pump a poor choice in some situations. Typically this occurs when it is cheaper to install an air-source heat pump that will provide 95% of the efficiency gains while costing less to install in an easier manner.
Ground-source heat pumps are expensive to install. These costs can be offset by higher energy efficiency and long-term energy bill savings but this is something you need to consider against alternatives such as air-source heat pumps.
Ground-source heat pumps are hard to install and can cause disruption. The permitting process can be complicated and the groundwork or borehole drilling are more labor intensive compared to an air-source heat pump. However, these are all temporary hurdles that, once overcome, can result in higher long-term gains.
Horizontal loop collectors take up valuable space. You can place parking spaces on top of them but you can’t build above them. If you plan on using a horizontal loop installation then you will not be able to build on top of the collector until it is not used any more. With a typical lifespan of ~50 years that can be a very long commitment!
How much do ground source heat pumps cost?
GSHP systems are more expensive than air-source heat pump systems as they require a more expensive and labour-intensive installation. It is very hard to provide a general estimate as to the cost of a system as the site and system sizing will play a significant role in system design and hardware selection. To get a rough estimate of such a cost please use our get a quote tool to get an idea of the costs involved, or speak to your local heat pump installer of choice.
Are ground source heat pumps worth the additional cost?
Ground source heat pumps carry a higher installation cost than air source units and this cost can vary significantly. For this reason it is hard to provide an answer to this question without knowing what the installation cost is for a specific project.
It is best to evaluate both options separately. Ask your heat pump installer to provide separate quotes for each solution for you to consider. The ground-source system will certainly cost more than the air-source system but the savings and system lifespan are also likely to be greater.
It is possible that other factors determine which solution is the best option for you, such as any subsidies for a particular installation, or site considerations and constraints. Whether you are considering a geothermal heat pump or an air-source heat pump, either option is typically a higher-performing investment than any other type of heating system.
How easy is it to install a ground source heat pump?
Ground-source heat pumps are not the easiest heat pump system to install. That is because the ground collector requires extensive ground work to install (in the case of horizontal collectors) or, a borehole needs to be drilled (in the case of vertical collectors). There may also be planning permission requirements that may take up time.
Despite this, the installation process itself can take as few as two or three days when there are no special site requirements. For a clearer picture as to how long an installation can take in your situation, you should consult a qualified HVAC or heat pump installer who has performed a site analysis and is aware of the local planning requirements.
What maintenance do ground source heat pumps need?
Ground source heat pumps don’t require complex, expensive or extensive maintenance, but it does need to be regular. In addition to the standard maintenance procedures typically followed for air-source units, the ground-loop may periodically need to be inspected for damage and flushing of the loop to remove air or debris from the system.
What is the life expectancy of a ground source heat pump?
The life expectancy of ground-source heat pumps is typically higher than any other heat pump type. That is partially because none of the heat pump components are exposed to the elements (such as external units for air-source heat pumps).
We generally anticipate a productive lifecycle of above 25 years for well-made ground-source heat pumps that use Copeland scroll compressors. You can find out more in our article on the life expectancy of heat pumps.
Can ground source heat pumps work with radiators?
Yes, most of them can! You can find out more about this by checking out our article on whether heat pumps work with radiators.
Why choose a TermoPlus ground source heat pump?
The TermoPlus TerraPump range is mostly suited to residential and small commercial use whereas the TermoPlus TerraPump Pro is our industrial / commercial heat pump range. We are also developing the TermoPlus GeoPump, our inverter-driven geothermal heat pump. The TermoPlus GeoPump can be used as either a ground or water-source heat pump and brings additional efficiency gains to an already robust and highly efficient platform.
Dependability: Our heat pumps are exceptionally reliable and have an above-average lifespan. We have been producing our heat pumps in Europe for more than 30 years and many of our first generation GSHPs are still in operation. We also use only the most reliable components such as Copeland scroll inverters to ensure dependable performance and a very long lifespan. Our typical GSHP product lifespan on average exceeds 25 years of use.
Efficiency: Our ground-source heat pumps offer an exceptionally high COP of 6.0 which can even reach 10.0 when combining the heating and cooling effects of the heat pump simultaneously. Multi-stage operation, custom system design and cascading allow for precise system sizing which enables the system to balance performance and efficiency perfectly. The inverter-driven GeoPump system can offer unparalleled precision and energy efficiency.
Support: We offer remote support to installers as well as system sizing and customization to ensure excellent product performance and maintenance directly from the engineering team that designs our products.
Flexibility: Our GSHP range is exceptionally flexible and modular to suit most needs and can be tailored further to match your system requirements and sizing specifications.
To find our more about what system would suit your needs best you can reach out to us for a quote and consultation.
Do ground-source heat pumps need planning permission?
It depends on the site, your local building regulations and the type of installation. Your zoning, the extent of ground works required and whether it will be a horizontal or vertical installation are likely to be play a role in planning permission. Small residential installations are often treated differently than larger commercial ones. Also, it your building is listed or if it is situated in a planned or gated community, in a conservation area or near archaeological sites, you are likely to face additional planning requirements and homeowner association (HOA) guidelines. Regional and local laws vary considerably so it’s advised that you check with your local heat pump installer and planning office.
Doesn’t heat transfer better in water-source heat pumps than in ground-source heat pumps?
While water-sources can generally facilitate faster heat transfer due to the higher heat transfer coefficient of water, there is no difference between ground-source and water-source heat transfer performance. That is because a ground-source heat pump’s collector length is designed to provide sufficient heat transfer surface to the ground, allowing for comparable overall heat transfer performance.
Disambiguation: There are several geothermal heating types. The International Ground Source Heat Pump Association makes a distinction between geothermal heat pump technology, which is what this article refers to, and other geothermal type solutions (which may be used by HVAC systems) such as Geothermal Direct Use and Geothermal Power.
Geothermal Heat Pumps (typical ground temperatures): ~4°C to ~21°C
Geothermal Direct (Hot Spring / Aquifer Temperatures): ~32°C to ~93°C.
Geothermal Power (Volcanic temperatures): ~93°C to ~371°C.
Source: https://igshpa.org/the-geothermal-spectrum/
