15 April 2026
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Aermec’s, Regional Sales Engineer, Barry Whyler, looks at how heat pumps are becoming the corner stone of the prison service’s decarbonisation strategy.
Prisons are resource-intensive but in common with other public institutions, the prison service is assessing the way its facilities operate. Naturally security orientated, their size and operation present several and unique challenges with many reliant on outdated systems that can contribute to increasing operational costs as well as environmental degradation. Nevertheless, a common denominator in prison services around the world is to improve their energy efficiencies. Great strides are being made to address infrastructure and architecture in the context of environmental responsibility and sustainability.
Estimates cite over 11.05 million people incarcerated across the world with the Unites States holding the most at 2.2 million. This results in significant environmental footprints using vast amounts of energy and resources. Last year’s Green Prison published by the United Nations (UN) asserts that all stakeholders including those detained can become agents for change and encourages greater sustainability to reduce prisons’ impact which can also improve working and living environments.
Worldwide efforts
A snapshot highlights what other countries are achieving: Finland considers carbon neutrality at the planning stage for all new prison infrastructure projects which includes thick insulation to mitigate temperature variations and advocates the installation of heat pumps. In Northern Ireland, the prison service uses a monitoring and targeting system so that energy usage in real time 24/7 can be measured. Netherlands is removing reliance on gas and fossil fuels. Canada has committed to phase out heating oil by 2028 and increase installation of heat pumps in all buildings including prisons. In New Zealand, the prison service’s sustainability approaches also include the use of heat pumps. While in Australia steps are being taken to ensure that new builds use heat pumps with further efficiency measures derived once the national grid decarbonises.
Here in the UK, the prison estate managed by the Ministry of Justice (MOJ), is undergoing a significant transformation to cut CO2 emissions and improve the efficiency and sustainability of facilities. The latest prison to implement targeted measures in support of the government’s net zero goals is Gloucestershire’s HMP Eastwood Park.
The challenge with aging buildings
Prisons are resource-intensive but in common with other public institutions, the prison service is assessing the way its facilities operate. Naturally security orientated, their size and operation present several and unique challenges with many reliant on outdated systems that can contribute to increasing operational costs as well as environmental degradation. Nevertheless, a common denominator in prison services around the world is to improve their energy efficiencies. Great strides are being made to address infrastructure and architecture in the context of environmental responsibility and sustainability. Estimates cite over 11.05 million people incarcerated across the world with the Unites States holding the most at 2.2 million. This results in significant environmental footprints using vast amounts of energy and resources. Last year’s Green Prison published by the United Nations (UN) asserts that all stakeholders including those detained can become agents for change and encourages greater sustainability to reduce prisons’ impact which can also improve working and living environments. Worldwide efforts A snapshot highlights what other countries are achieving: Finland considers carbon neutrality at the planning stage for all new prison infrastructure projects which includes thick insulation to mitigate temperature variations and advocates the installation of HMP Eastwood Park Falfield Gloucestershire April/May 2026 ASHP Aermec.indd 8 Not dissimilar to small towns, prisons operate 24/7, are densely occupied and consume significant amounts of energy. A key challenge is the ageing condition of much of the prison estate which can make retrofitting challenging and costly.
But HMP Eastwood Park in Gloucestershire has already started decarbonising its estate. Two prison blocks, originally constructed in the 1960s, are undergoing upgrades to reduce energy costs and carbon emissions. This initiative focuses on installing Aermec heat pumps and improving insulation at the closed category prison in South Gloucestershire for up to four hundred women aged eighteen and over.
The decarbonisation programme
Outdated gas boilers are being replaced with Aermec heat pumps thanks to £3 million secured in funding from the Ministry of Justice (MOJ). Prisons are complex public sector sites and carbon intensive. In addition to installing air source heat pumps, additional measures will also be implemented as part of the decarbonisation programme. These include improved roof and cavity wall insulation, an upgraded pumping system, building management system (BMS) upgrade, and the installation of new double-glazed windows.
Delivery of these practical steps are designed to reduce energy consumption, lower operational costs, and diminish the prison’s carbon footprint. Despite operational, technological, and financial challenges posed by aged buildings combined with the historical significance of many buildings, prisons like HMP Eastwood Park are undergoing energy efficient upgrades. HMP Eastwood Park’s efforts form part of a nationwide initiative that aims to reduce the carbon footprint of public sector buildings which sets and example and reflects the MOJ’s commitment to environmental responsibility.
Improved energy use
It is anticipated that the prison will benefit from lower carbon emissions due to improved energy use. By installing air source heat pumps, the prison will also reduce overall energy costs. These changes contribute to meeting the government’s goal of net-zero emissions by 2050 and support long-term sustainability within prison estates.
Four reversible air source heat pumps (ASHPs) are being installed using R32 refrigerant, a low GWP (GWP of 675) which reduces the environmental impact of HVAC systems, with extensive attenuation packages to reduce the operational noise levels and provide acoustic comfort in the complex. Although designed for dual functionality, to provide chilled water for cooling and high temperature hot water, the units will be providing heating only. There is a cascade arrangement with the NRG ASHPs producing a water outlet at no more than 450C. This source water feeds Aermec’s WWB units where heat is extracted from the source water. The source water then returns to the ASHPs at 400C and the ASHPs continue to raise the water temperature back up to 450C.
The WWB water-to-water units will concurrently output higher temperature water (the maximum is 800C) that provides the heating. The output temperature was designed to provide heating at 780C/800C. Four water-to-water heat pump units are in one prison block due to a larger size and heating demand whereas three further units are in a smaller building where three WWB 900 units are sufficient. The main use of the hot water generated is for central heating but also domestic hot water (DHW) for showers, cleaning, and other ancillary functions. Aermec developed the irreversible (heating only) WWB 900 water-water heat pump units for this project with the aim of guaranteeing high efficiency at full and partial load. Designed for indoor installation where the application requires hot water at high or extremely high temperatures from a low or medium temperature source, features include highly efficient compressors, plate heat exchangers with reduced pressure drop and two independent cooling circuits.
Irreversible units are designed for dedicated heating or cooling operations. The plate heat exchangers efficiently transfer heat between fluids with minimal energy loss. The two independent cooling circuits enhance reliability and operational flexibility by ensuring that even if one circuit requires maintenance, the system continues operating without interruption.
These features ensure consistent performance, lower energy consumption, and greater reliability, making the water-to-water units ideal for demanding industrial or commercial heating needs.
MOJ’s net zero goals
The MOJ is implementing similar upgrades across its entire estate with the construction of new build greener prisons whilst upgrading legacy facilities using the latest technologies and recycled material as part of its on-going strategy to meet net zero goals. Beyond direct carbon reduction initiatives, programmes are being implemented to align prisons with the green economy and to help offenders acquire and develop skills and training that can equip them for jobs in sustainability upon their release. These include improving biodiversity. Eastwood Park was the first prison to be awarded National Plant Collection status by the conservation charity Plant Heritage. The prison’s collection focuses on eleven species of wild garlic known as Tulbaghia, which is known for its resilience and medicinal uses. This recognition underscores the prison’s dedication to plant conservation and provides educational opportunities for staff and inmates.
These initiatives help to foster a sense of community environmental stewardship and improve wellbeing within the prison.
Prisoners also participated in an exhibition held by the Royal College of Nursing Library and Museum and Koestler Arts, where their artwork focused on the history of prison nursing and featured themes exploring resilience and care.
The prison’s education department has previously been nominated and won a Governor’s ‘Value Champion Award for teamwork. The team helped deliver and support education for women from entry level qualifications through to full degrees.
The MOJ which conducts extensive analysis encompassing greenhouse gas emissions to waste management and recycling as well as employment and training. The re-introduction of gardens supplies prison kitchens with produce, but also improves the health of those incarcerated, equipping them with new skills that aid reintegration and reduces emissions. The legally binding Paris Agreement of 2015 requires signatory states to establish a climate action plan that is updated every f ive years and translated into action. The MOJ is in alignment with those aims. Work started at HMP Eastwood Park in January last year and will be completed by October 2026. The heat pumps will generate significant costs savings, demonstrate operational efficiencies, environmental stewardship as well improving the wellbeing for imprisoned people, staff, and support services.
