In England, when the north-east winds blow across the Fens to Cambridge, ageing gas boilers within the medieval buildings of the university struggle to keep students warm. To compensate for raw conditions brought by the ‘Beast from the East’ and other cold snaps, radiators run at 80°C, churning out heat that leaks through rattling windows.
But nearby there is a source of free heat – from the ground, from the River Cam, even from the air – and if advocates of heat pumps have their way, university buildings hundreds of years old will eventually be warmed by lower-carbon energy. If thermal energy could be stored and recycled here and across the UK, hefty emissions caused by heating could fall dramatically.
When Professor Andy Woods oversaw a small experiment at St John’s College, Cambridge, to turn the temperature in the central heating pipes down to 60°C to mimic heat pump temperatures, no one complained – even when it dropped to zero outside. Radiators stayed on for longer and temperatures inside only dropped by a degree or so. “So we know we could keep people comfortable for most of the year with a heat pump,” he says.
This is just a tiny trial, says Woods, who is head of the university’s Institute for Energy and Environmental Flows, but the potential of imaginative ways to harvest, store and use thermal energy is huge. “We should be trying out things and, as we do more, we will get better and better solutions,” he adds.
Keeping buildings warm accounts for 17% of carbon emissions in the UK. Heat pumps and heat networks, powered by renewables, are seen as the most efficient method to decarbonise, and a crucial part of the UK’s path to net zero. They are enthusiastically championed by policymakers – the less dependent the country is on imported gas, the less vulnerable it is to rising prices.
Woods is investigating how seasonal temperature fluctuations allow thermal energy to be used, stored and recycled efficiently. As proof of concept, this might be via an array of bore holes – possibly drilled in a corner of the picturesque college grounds – to harvest underground warmth in winter to supply heat pumps that can raise temperatures further.
In summer, heat could be recycled by copying southern Europe’s use of dark-clad pipes and water tanks on roofs to absorb summer sunshine. Warmed liquid could be piped directly back into the ground to reheat the rock around the bore holes above ambient temperatures, ready to dispense heat the next winter. Even heat from river water, which can reach up to 20°C in summer, could be extracted and stored underground.
On a larger scale, he says, aquifers – permeable rock that holds water – could be warmed by summer thermal energy. Heat could be exchanged between a hot and cold well, giving cooling water in summer and warm water for heat recovery in winter. “After a couple of years, you get about 95% of that thermal energy back,” says Woods. “It’s very efficient. You minimise demand on the grid.”