Heat pumps alone are not a magic bullet for school net zero


03 January 2024

The race is on to decarbonise heating in schools across the country. Rob Smelt, of low carbon consultancy BREng, highlights the challenge and opportunities this presents, and the role heat pumps will play in combination with other renewable technologies.

There are 32,226 schools in the UK, including around 4,000 secondary schools. Add the UK's 142 universities – in themselves effectively small towns, and circa 400 Further Education colleges, and the national education estate amounts to a very substantial and diverse network of multi-use buildings, with complex HVAC requirements.

In terms of energy use, the scale of consumption across the education sector is very significant. Total annual energy consumption by education buildings is estimated to be a staggering 11,378 million kWh of energy, equivalent to 25% of total public sector energy use.

The requirement to decarbonise school buildings poses a major challenge for the sector. It will require every establishment to come up with a plan to achieve net zero carbon emissions within a defined timetable.

The national UK target of 2050 mandated in law is somewhat misleading, as some local authorities have adopted much faster net zero deadlines for public buildings in their areas.

For example; major cities such as London, Birmingham and Bristol have set a target to be net zero by 2030. Manchester has a target of 2038.


Plans need to be put in place now

In practice, therefore, education estate managers should be putting plans in place now to map out their route to net zero.

Unfortunately, due to the diversity of school building types, usage patterns and existing energy systems, it is not possible to apply a single template to deliver net zero. No one model could possibly cover the complex reality on the ground.

It requires a school-by-school approach. This starts with a detailed survey of existing HVAC infrastructure, taking into account the specifics of building fabric, insulation, glazing, orientation, design and lay-out – down to heating provision and occupancy levels of individual spaces at the classroom level.


Impossible to ignore

Heat pumps have been held up as a major technology solution in the effort to decarbonise heating, and rightly so. From a thermodynamic perspective, the fundamental efficiency of heat pumps is impossible to ignore.

Their ability to harvest low grade heat energy from the environment and upgrade it into a useful form to heat and cool buildings gives them a big advantage over alternatives.

While the most efficient forms of gas heating approach Coefficients of Performance (COPs) of less than one, modern heat pumps can achieve COPs many times this. As a result, heat pumps can generate several times more energy than they consume, far outstripping rival approaches.

This, coupled with the fact they are proven technology, sets heat pumps apart among competing low carbon solutions, and means they will have a huge role to play in helping schools on the journey to net zero.

As well as helping to reduce carbon emissions for individual buildings, heat pumps have an important part to play in reducing emissions through their use in distributed heat networks.

This is particularly relevant for larger education estates, such as universities and colleges, where the combined heating requirements are greater and economies of scale deliver the highest savings.


Challenges with occupation

In terms of public buildings, schools are unusual in being occupied for only part of the year. In term time, usage is very intense, with high occupancy density. During holidays, occupancy falls dramatically, in many cases to zero. This presents schools with both challenges and opportunities for achieving net zero carbon.

High occupancy and intense usage during term time requires suitably powered HVAC systems to cater for heating, cooling and ventilation requirements.

Adequate heating capacity is particularly important to ensure comfortable conditions at the start of the day. However, due to

the high-density occupancy, particularly in classrooms and high-use corridors, heating demand can fall rapidly due to the thermal contribution of pupils to the space.

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This requires careful control of individual rooms to ensure the natural heat gain that occurs throughout the day in classrooms

is taken account of, and heating inputs managed accordingly.


Combined with other technologies

As efficient as heat pumps are, the reality is that they are not sufficient on their own to deliver net zero for most schools. They must be used in combination with other technologies.

Having carried out detailed HVAC and energy surveys of scores of schools, for the reasons outlined above it is clear that the precise solution will be different in almost every case. It is likely to involve a mix of heat pumps, solar PV, LED lighting, upgraded heat emitters, insulation and high efficiency ventilation.

Use of photovoltaic panels is particularly attractive in combination with heat pumps. Firstly, they provide an additional source of renewable energy to supplement that generated by heat pumps, helping to further reduce use of primary high-carbon electricity.

Secondly, as schools are not occupied for significant periods of time, particularly during the summer when solar energy is greatest, the surplus power produced can be returned to the grid to offset primary electricity used when the school is occupied.


Additional power

Thirdly, PV systems contribute helpful additional electrical power, which can be valuable for schools with limited power headroom, stretched by the higher power demand from installing heat pumps. This may help overcome the need to invest in upgrading power supplies, which can be a significant additional capital cost.

Lighting is another area where worthwhile gains can be made. Lighting represents around 8% of schools' energy use, and 20% of their energy costs.

Upgrading to modern LED lighting reduces electricity use by around 80%, compared with traditional technology, contributing a useful saving in the overall energy budget.

Heat pumps in combination with PV systems and LED lighting can deliver very significant reductions in school carbon

emissions. To fully optimise buildings, however, it often requires fine tuning HVAC systems with upgraded heat emitters, improved insulation and the use of modern monitoring and control systems.


No single magic bullets

While this is the main palette of technology options, it is important to stress that there isn't a single magic bullet to deliver net zero. Schools are complex estates, with diverse designs, legacy technologies and usage patterns.

This requires each site to be approached afresh, and the challenges and opportunities for achieving net zero assessed with an open mind in the light of the specifics, in each case.

Once a solution has been designed, installed and commissioned, the process doesn't stop there. In our experience, there are often significant additional gains that can be made by optimising the system in the light of how it operates in practice.

Following the completion of a number of school decarbonisation projects over the past couple of years, we are now working with schools on fine-tuning systems – to further reduce energy bills, cut carbon, and ensure pupils and staff benefit from the most comfortable and productive environment possible.

With 30,000 plus schools requiring decarbonisation, this is going to require a huge national effort. When considered alongside the wider challenge of decarbonising all public and private sector buildings, it is truly an epic undertaking.

The key is starting now, and making use of the valuable lessons learned by the early adopters pioneering on the net zero frontier.