Research and analysis

Environmental impacts of temperature changes from ground source heating and cooling systems: summary

Published 6 September 2024

Applies to England

1. Chief Scientist’s Group report summary

This project examined the potential for ground source heating and cooling (GSHC) systems to change the temperature in the ground around them and identified receptors that could be impacted by these changes. The project also assessed possible growth of the industry in the next 5 to 10 years. These findings will help the Environment Agency and others understand where the environment is at greater or less risk of temperature changes in the ground around GSHC systems.

1.1 Background

Heat pumps use the temperature from their surroundings to heat or cool a space such as a building. As part of the government’s 2020 net zero ambitions, the number of domestic heat pump installations could increase to 600,000 a year by 2028. GSHC systems are a type of heat pump that use the relatively constant temperature of the ground as either a source of heat or cooling. Broadly, they follow two designs: some use fluid circulated within a borehole to exchange heat (closed-loop) whereas others abstract and reinject groundwater from an aquifer (open-loop). Taking heat from the ground causes it to cool, and injecting heat warms the surrounding ground.

The project assessed the potential for temperature changes in the ground around GSHC systems of different sizes and in different geological settings, identified changes within the environment that could occur due to these temperature changes, and considered the receptors that could be sensitive to these changes. Finally, it reviewed how widespread these impacts might be due to development of the industry.

1.2 Approach and findings

Temperature changes in the environment around GSHC systems: thermal plume modelling and literature review

This report examines the temperature changes (thermal plumes) in the ground around closed-loop GSHC systems through a literature review and numerical modelling. The development of thermal plumes was simulated using flow, mass and heat transport modelling software. The impact of different GSHC system characteristics and geological settings were investigated by varying individual parameters and through 7 scenarios.

Thermal plumes were defined as the region around a GSHC system that experiences a 1oC temperature change or more, since groundwater temperature is in general quite stable. The factors that have the greatest influence on thermal plume development are groundwater flow, bulk thermal conductivity and GSHC capacity (kW). Groundwater flowing past the GSHC system disperses the heat put into the ground; more groundwater flow results in a cooler but longer plume. Relatively high temperatures can build around GSHC where ground thermal conductivity is low. In our models, thermal plumes around household-sized closed-loop GSHC systems (<45 kW capacity) only travel about 10 m. However, thermal plumes for GSHC system that could supply a network, large building or campus (up to 200 kW capacity) could travel up to 300 m.

Identifying potential receptors to GSHC systems

This part of the project created an interactive systems map of processes and receptors (e.g. people, animals, property) that could be impacted by temperature changes in the ground around GSHC systems. Information for the systems map was gathered through a literature review, workshops, and surveys with 32 subject matter experts.

The systems map shows realistic pathways through which receptors could be impacted by temperature changes in the ground around GSHC systems. These include direct (temperature changes) and indirect (for example, changes in water chemistry) impacts. The map is divided into connected sub-systems areas including: aquifers; groundwater dependent ecosystems, wetlands and springs; surface waters; water quality and resources; buildings and infrastructure; soils and geomorphology, and other GSHC infrastructure. Further information on the processes can be viewed by clicking their nodes in the map. The main environmental impacts from temperature changes around GSHC systems include geochemical reactions and contaminant mobilisation, and changes in microbiological, plant and animal communities. In general, receptors appear more sensitive to increased, rather than decreased, temperatures.

GSHC: status, policy and market review

In this part of the project various sources of data, including published literature, reports and interviews with members of the industry, were used to assess the likely number of existing GSHC systems in England over time. The report reviews trends across England and discusses barriers and drivers to industry growth. The findings were used to estimate market growth for GSHC systems over the next 5 to 10 years.

Despite challenges in estimating the numbers due to a lack of complete records, it is thought that there are between 30,000 to 38,000 GSHC systems currently installed in the UK. Over the last decade, the average number of new installations a year is 3,200 (increasing to 5,584 in 2022). Historical trends and industry views indicated that the number of installations in the next 5 to 10 years is highly uncertain. Most installations are closed-loop, but there could be a small increase from 16 to 30 open-loop installations per year. Based on current and planned policy and trends, future household-sized closed-loop installations (less than 45 kW) could be between 5,000 to 20,000 a year (currently about 2,000) and there could be more than 150 larger non-domestic installations (more than 100 kW) per year (currently about 60 to 80).

1.3 Conclusions

This project has shown that in many cases temperature changes in the ground around GSHC installations are likely to be limited. However, impacts could be greater in particular geological settings and for larger GSHC systems. A range of receptors in groundwater and connected environments could be impacted directly and indirectly by temperature changes. With a possible growth of the GSHC industry over the next 5 to 10 years, this information can be used by the Environment Agency and practitioners to identify settings where the effects of temperature changes would be higher or lower. It should also be noted that there are other factors that can contribute to changing temperatures in the environment.

1.4 Publication details

This summary relates to information from project SC220017, reported in detail in the following outputs:

*Temperature changes in the environment around ground source heating and cooling systems: thermal plume modelling and literature review (SC220017/R1) * Identifying potential receptors to ground source heating and cooling (SC220017/R2) * Ground source heating and cooling: status, policy and market review (SC220017/R3) * Systems map

Project manager: Sian Loveless, Chief Scientist’s Group

Research contractor: Mott MacDonald

This project was commissioned by the Environment Agency’s Chief Scientist’s Group, which provides scientific knowledge, tools and techniques to enable us to protect and manage the environment

Enquiries: research@environment-agency.gov.uk.

© Environment Agency