Wolfson College, University of Oxford

To keep disruption, cost and embodied carbon to a minimum, we devised a strategy to keep the existing radiators and pipework and worked with the college to ensure it could be occupied throughout the programme of upgrades. We opted for an air-source heat pump system, using an innovative low environmental impact CO₂ refrigerant (rather than a more damaging refrigerant). The project is one of the largest CO₂ heat pump programmes undertaken in the UK and one of the first to use CO₂ refrigeration for space heating at this scale. We have also made many rationalisations to the mechanical systems to reduce energy consumption more generally – radically reducing pump sizes and the extent of distribution pipes.

Our calculations established that replacing windows, roofs and insulation alone has reduced the buildings’ annual heat losses by 80%. Energy consumption data over the first year showed that gas consumption reduced by more than 60%, while electricity consumption barely increased. The losses in the hot water distribution system have reduced 40%. In the first year, the reduction in pumping energy largely offset the additional electricity consumption of the heat pumps, 

The total reduction in carbon emissions is calculated to be more than 80% over the next 20 years, however the College now procures 100% renewable electricity and so the reduction in operational carbon emissions is 100%.

High planning and heritage standards for the Grade II-listed building meant that choosing the correct glazing was crucial. Following extensive research by the architect Original Field of Architecture, the team opted for Cuin glass, a material that has the performance of triple glazing with the thickness of double. This allowed the heritage sightlines to be preserved without compromising the aesthetic of the building while achieving excellent thermal performance.

We led the college’s successful application to secure £6M of SALIX Grant funding, which covered 65% of the first phase works and some proportion of the second phase. We are working with the college to help them promote and explain the project to their residents and alumni, to help them secure support for the later phases of the work.