The Wolfson College Decarbonisation Process

Wolfson College was founded in 1966 to combine modern values with academic excellence, providing graduate students and Fellows with an egalitarian home by the Cherwell River. Its cherished Brutalist buildings by Powell and Moya were completed in 1974 and are now Grade II listed. However, its design, before the 1970s oil price shocks, does not reflect the College’s commitment to a minimum impact on the environment. Wolfson College currently has a twenty-year carbon footprint of an estimated 24,000 tonnes of CO₂, much of which relates to heating.

Decarbonisation of heating is difficult, as the economic argument for investment is simply not there, which precludes much of the progress. The Department for Business, Energy and Industrial Strategy (BEIS) is very aware of this and looking for creative solutions that will meet politicians’ approval. Ironically, the pandemic provided such an opportunity and the government made £1bn available to fully fund decarbonisation projects in the public sector: part stimulus package, part decarbonisation.

Salix Finance organised the grants in September 2020. My colleague, Ali Shaw, made our Practice aware of the opportunity and we went about broadcasting it to many of our public sector clients. Reaching out to schools and colleges in Oxford didn’t initially generate much response, as these institutions had much more pressing concerns, such as staying open, solvent and safe during the pandemic.

However, Wolfson College, Oxford had recently established decarbonisation as its number one priority in its new Estate Strategy and was already investigating funding opportunities. There was, therefore, an immediate meeting of minds between Richard Morin, the Bursar of Wolfson College, and myself: the College faced an uphill struggle given the cost of replacing the windows on their 20th century listed building and the other measures needed, and Max Fordham were keen to show what could be done to decarbonise a large, complex estate.

To secure part of the £1bn Salix grant, we needed to move fast. There was no cap, the grants were issued on a first come first served basis, and the money needed to be spent by March 2021 or at a stretch September 2021. We applied based on a proposal to replace the windows, insulate the fabric and replace the gas heating with a CO₂ heat pump. Although Salix were very sympathetic to our initial bid, we missed out on the first round of funding as our project simply wasn’t advanced enough to be completed within their tight timeframes. However, the successful uptake of the grants resulted in the announcement of another grant round - Phase 2 - in April 2021, and this time we were ready, with the project quite well developed. This fund was much smaller at £75m, more proscribed in what it would pay for, and it had a bid limit of £5m, so required the College Governing Body to agree to make a £3M contribution (which it did by taking some risks and reorganising its finances). This time our application was successful! The result of the combined funding was a well-considered and novel retrofit decarbonisation project that could be completed in just under a year.

The generous funding via Salix has allowed the College to pursue the plans set out in its 2020 Estate Strategy: making decarbonisation its top priority and commissioning us (Max Fordham) to complete an energy audit and decarbonisation plan, and to oversee the project. Through this audit I established that replacing the windows (of which there are over 1,000!) and doing all the combined insulation methods would lead to an 80% reduction in the buildings’ annual space heating requirement. In addition to this, replacing the original 50-year-old gas boilers (that currently provide the heating and hot water) with modern heat pumps running on clean electricity would reduce the main estate’s carbon footprint by at least 75%. The College is now on a program to replace its extensive elevations of single glazing with new, thermally-broken, aluminium frames with CUin glass, which claim to have an extraordinarily low mid-pane U-value of 0.4 W/m²K.

Bringing the heat loss down will make it is easier to provide the heating with a heat pump. Having a river nearby and land for a ground array, the College was spoilt for choice for a source of heat. We decided on air as the simplest and cheapest-to-install reliable heat source, although the noise and cold airflow had to be carefully considered. We wanted to avoid an environmentally damaging refrigerant and (ironically) chose a CO₂ sealed system (the greenest of refrigerants) that is now common in supermarkets, but not in other buildings. The trans critical cycle can produce high temperatures of 75°C, but the efficiency of the system relies on getting water back at a low (less than 34°C) temperature.

While heat pump technology has been around for a few years, this will be one of the largest heat pump programmes ever undertaken in the UK and one of the largest to be retrofitted to an estate of this complexity.

The existing pipework is being retained and reused (otherwise the project would be completely unviable in terms of both cost and disruption) and we are re-using the existing radiators that will become oversized when the new windows are fitted. Using the features of the trans critical system, we will be sending out heating water at 75°C at peak heating times but restricting the flow through the radiators such that the return is cool. The average radiator temperature will be reduced to match the reduced heat loss and the radiator valves will be replaced with return temperature limiters to ensure that the water coming off the radiator is cool.

The peak heating load at an external air temperature of -4 °C is expected to be 900 kW. This will be met with two 350 kW heat pumps and a 300 kW back up direct electric heater. The peak heat requirement for domestic hot water is not as great as the winter heating, but it is required all year, so it makes up a large part of the annual energy consumption. Half the energy is needed to meet the domestic hot water load, while the other half is needed to keep the circulating hot water hot. At times in the summer, the circulating hot water will be the only load in the building. The CO₂ heat pump isn’t suitable for this, as there isn’t a big temperature gradient, so we are installing a group of domestic heat pumps that will run continuously. At these times the heat from the CO₂ heat pump will still be used to heat the water up from cold.

One big challenge of moving from gas-fired heating to electric is that it does require much more power to the site. A key aspect to the project was the upgrade of the transformer from 400 kVA to 1200 kVA and the routing of big cables from the transformer to the heat pumps.

The College has received their first tranche of money and the initial project, which includes the change to electric heat pumps and the replacement of around 70% of the windows, is programmed to be complete by the end of February 2022.

To get to net zero across the whole of its estate of over 15,000m² of gross internal floor area of work and living space, more work will need to be done, but the current project will certainly break the back of carbon emissions at the College.