UK schools rethink green heating – are ASHPs failing on old infrastructure?
The push for greener heating solutions in UK schools saw a surge in the adoption of Air Source Heat Pumps (ASHPs) in recent years, driven by government incentives and a commitment to reducing carbon emissions. However, a growing chorus of concern is emerging, suggesting that these systems, while theoretically efficient, are proving problematic and potentially wasteful when installed in older school buildings.
The question now being asked is: are schools considering a return to, or an adaptation of, existing heating systems, or perhaps a complete shift to air-to-air heat exchange systems, to address the shortcomings of ASHPs in unsuitable environments?
The promise and the problem of ASHPs
ASHPs work by extracting heat from the outside air, even at low temperatures, and transferring it indoors. They are significantly more energy-efficient than traditional gas boilers, leading to lower carbon footprints and, in theory, reduced running costs. The government's Public Sector Decarbonisation Scheme (PSDS) heavily incentivised their adoption in schools.
However, the reality on the ground is proving more complex. Many UK schools are housed in older buildings, often poorly insulated and with outdated radiator systems designed for the high-temperature output of gas boilers. ASHPs, in contrast, operate at lower temperatures, requiring larger radiators or underfloor heating to distribute heat effectively.
The infrastructure bottleneck
The core issue is the mismatch between the technology and the existing infrastructure. Schools are facing a range of problems:
- Inadequate Insulation
Older buildings leak heat rapidly, meaning ASHPs have to work much harder, negating their efficiency gains and leading to higher energy bills. A report by the National Audit Office (NAO) highlighted concerns about the performance of energy efficiency measures in buildings, including the impact of poor insulation. (National Audit Office - Achieving Net Zero - See section on "Decarbonising the existing building stock"). - Undersized Radiators
Existing radiators, designed for high-temperature systems, are often too small to distribute the lower-temperature heat produced by ASHPs effectively. This results in cold classrooms and inconsistent heating. - Costly Retrofits
To make ASHPs work effectively, schools often need to undertake extensive and expensive retrofitting, including replacing radiators, improving insulation, and potentially installing underfloor heating. These costs can quickly outweigh any potential savings from lower energy bills. - Complex Installation and Maintenance
ASHPs are more complex systems than traditional boilers, requiring specialised installation and maintenance, which can be difficult and expensive to source.
Insufficient Hot Water: Some schools that rely solely on the ASHP are finding that they are struggling to provide sufficient hot water at peak times.
The Financial Strain
The initial investment in an ASHP is substantial, and the added costs of retrofitting are pushing many schools' budgets to breaking point. Reports are emerging of schools that have spent significant sums on ASHP installations only to find that their energy bills have increased, and their classrooms are colder. This is a far cry from the promised cost savings and environmental benefits.
Is air-to-air a potential solution?
One alternative that might be considered is the Air to Air heat exchange system. These systems directly transfer heat from one airstream to another. They can be installed in a modular fashion, targeting specific areas or rooms, and often require less extensive infrastructural changes than ASHPs.
SCOP advantage – air-to-air vs ASHP (wet system)
A key advantage of air-to-air systems in this context is their potentially higher Seasonal Coefficient of Performance (SCOP). SCOP measures the efficiency of a heat pump over an entire heating season. While a well-installed ASHP in a well-insulated building with underfloor heating can achieve a high SCOP (perhaps 3-4), an ASHP connected to an existing, undersized radiator system in a poorly insulated building will likely see a significantly lower SCOP, potentially dropping below 2.5 or even 2. A report by BESA found that, when combined with mechanical ventilation, "air to air systems have demonstrated up to 71% lower energy usage compared to an equivalent baseline system". (BESA - Indoor Air Quality and Ventilation)
Air-to-air systems, because they deliver heat directly into the air and are less reliant on the existing water-based infrastructure, can often achieve a higher SCOP in these retrofit scenarios. SCOPs of 4 or even higher are achievable with modern air-to-air heat pumps. Whilst we couldn't find a single perfect source comparing specifically school-based ASHP vs Air-to-Air SCOPs, combining the BESA report on air-to-air efficiency with general information on ASHP SCOP degradation in poor conditions (like those described in the NAO report) strongly supports the argument. Many manufacturers, such as Daikin, provide product information highlighting high SCOP values for their air-to-air systems.
Another option is to have traditional gas or oil boilers as backup, however, this is not deemed very environmentally friendly.
A call for re-evaluation
The situation highlights the need for a more nuanced approach to decarbonising school heating. A "one-size-fits-all" solution is clearly not working.
Key recommendations include:
- Thorough Building Assessments
Before any heating system is installed, a comprehensive assessment of the building's fabric, insulation, and existing heating infrastructure is crucial. - Targeted Funding
Government funding should be more flexible, allowing schools to choose the most appropriate heating solution for their specific circumstances, rather than being tied solely to ASHPs. - Phased Implementation
A phased approach, starting with improvements to insulation and radiator upgrades, may be more financially viable and less disruptive than a complete system overhaul. - Consideration of Alternatives
Schools, along with their advisors, should carefully explore alternatives to ASHPs, such as air-to-air systems or even improved, highly-efficient gas boilers in the short term, alongside a long-term plan for deeper decarbonization. The Department for Education itself acknowledges the need to consider a range of heating solutions. Department for Education - Good estate management for schools (See section on "heating systems").
The drive to reduce carbon emissions in schools is essential, but it must be done in a way that is both effective and financially sustainable. The current challenges with ASHPs in older buildings highlight the need for a more pragmatic and tailored approach, ensuring that schools can provide warm, comfortable learning environments without breaking the bank. A rushed, poorly-planned approach risks wasting public money and ultimately undermining the broader goals of decarbonisation.