In the third of the series of blog posts regarding technologies for retrofitting homes to be more sustainable, PJH are looking at ground source heat pumps. Beginning with an introduction and facts regarding GSHP’s, pros and cons, costs for an average home, potential payback timeframes and the required space for a ground source heat pump retrofit.
Ground Source Heat Pump Retrofit Introduction
According to the Department for Business, Energy & Industrial Strategy (2021) during 2020, the UK residential sector accounted for 20.8% of all carbon dioxide emissions.
The UK Government has set out the goal to become net zero by 2050. Part of this involves a gas boiler ban as early as 2025 for new build properties. Existing gas supplied heating systems will be unaffected, but as fossil fuel prices become increasingly higher it’s ever more pertinent to explore alternatives, with assistance through the boiler upgrade scheme available.
It’s not always achievable to address all the sustainability issues of a dwelling in one go. Creating a retrofit plan for renovations and upgrades towards an end goal will help reach the desired level of integrating ‘green’ energy saving technologies into your home.
Ground source heat pumps (GSHP), like air source heat pump (ASHP) utilise the heat from outside your home in order to heat radiators, underfloor heating and hot water tanks. However, GSHP utilise either trenches or boreholes in order to heat the system. This method of heat recovery is highly consistent and energy efficient due to the reliability offered by ground temperatures. When utilised with the lower running temperatures of an underfloor heating system, the ground source heat pump retrofit is able to provide consistent heating. They work by having a liquid circulate through the loop of pipes underground and into a heat exchanger in the dwelling which compresses the liquid to raise its temperature to heat radiators/hot water systems. GSHP’s also have a great lifespan with most of the infrastructure able to last 70 years or more and typically only requiring annual checks for maintaining warranties. Like with an ASHP, for a GSHP system to be effective it is best to ensure the property is as well insulated as possible, at least to current building regulations, in order to heat effectively and maintain comfort levels within a dwelling.
Ground loop (trenches) system
In order to be able to utilise a ground loop system, the property must have adequate space, access for excavating equipment and have suitable ground conditions (soil type, vegetation etc). The length of the ground loop depends on the size of the house and system required.
Borehole system
The borehole system is able to provide dwellings with limited space, access to the benefits of GSHP’s (for an added premium of excavating the boreholes). These vertical borehole systems require thermogeological ground surveys to provide thermal characteristics of the site and accurate depths in order to achieve the best heat recovery per metre of a borehole. Larger dwellings may require more than one borehole depending on the heating demand and the underlying geology. They are around 180mm in diameter and vary in depths of between 75-200m.
Pros and Cons of Ground Source Heat Pump Retrofit
Costs – For an Average 3 Bed Semi-Detached House
Different factors can affect the cost of a ground source heat pump retrofit system, the main factor would be the amount of space available as this would determine whether a property can benefit from a ground loop system or would require a borehole system. The size of the dwelling and requirements for the system will also have a determining factor on the cost, as larger dwellings require larger systems and more powerful pumps. Ground loop systems require larger physical space requirements but offer lower construction costs. Borehole systems can vary in cost depending on the depth of the borehole, design and construction, location, and geology/hydrology of the site.
For a 3-bedroom semi-detached property, according to the Energy Saving Trust (2023), it costs on average £24,000 for a ground loop system and up to around £49,000 for a borehole system. With government subsidies available to aid in the upfront costs, you could benefit from a £6,000 grant as part of the ‘Boiler Upgrade Scheme’ and also 0% VAT on purchases.
Running costs and potential savings depend upon the system the ground source heat pump retrofit is replacing. The graph shows the different types of systems and their associated annual savings (based on October 2022 fuel prices). In order to maximise the slow release and lower running temperatures within existing homes, additional measures and systems are required. Underfloor heating for example is a perfect candidate for GSHP systems as the large surface areas produce evenly distributed heat within a room.
Further costs can be saved dependent on the temperature the end-user has the system set at, the fabric of the building and how well the envelope of the house can retain heat.
Payback Timeframe for an Ground Source Heat Pump Retrofit System
The payback timeframe of a GSHP depends upon the system that it is replacing. According to the annual savings graph, when replacing an old oil powered boiler, there are savings of around £375 annually, whereas if it is replacing an old LPG powered boiler then savings can be as high as £860 annually. If we were to assume that the property has an old mains gas powered boiler, with savings as much as £670 and a government subsidy of around £6,000 then the payback timeframe for a ground loop system would be around 26 years. However according to the Eco Experts (2023) GSHP’s can last as long as 70 years compared to the 10-year life span of gas boilers leading to further savings of around £4,000 every 10 years by not having to replace a gas mains powered boiler to be considered. When considered this further reduces the payback time.
Required Space for a Ground Source Heat Pump Retrofit System
The size of the system required for the dwelling will vary dependant on how much space will be needed for the internal unit that needs to be installed. It is something that needs to be considered early on in the decision-making process as it would take up more room than a typical airing cupboard that houses a boiler. To be able to house the heat pump, hot water cylinder and buffer vessel (if required) it can require around 2.1m x 1m. These can be situated in a variety of locations but it is best to consider ahead of time and determine whether you want it installed within utility/garage/dedicated plant room.
Conclusion
In conclusion, there are two ground source heat pump retrofit systems available to benefit a dwelling, ground loop and borehole. Requiring different amounts of space, they can benefit even homes with limited amount of land. Providing consistent heating year-round due to reliable ground temperatures. They have a long lifespan with estimates of equipment lasting up to 70 years with minimal maintenance. However the large upfront costs and space requirements can deter people from seeing this as a true contender in sustainable/‘eco’ retrofitting measures. You can also claim up to £6,000 as part of the government’s ‘Boiler Upgrade Scheme’. Additionally, they are highly efficient and safer than combustion boilers with a low carbon footprint and low maintenance requirements.
Ask us for advice
If you have a project in its infancy and want to have an informal chat regarding your options, feel free to contact us, we are always happy to provide friendly and knowledgeable advice. Get in touch on 0161 460 0382 or email the team at enquiry@pjhas.co.uk
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