HEAT PUMP | PEMBROKE COLLEGE that you want, explains Gustafsson. The lower-temperature heating mains make it more of a challenge to deliver heat to the sites refurbished buildings. These were originally heated using traditional gas boilers with heating circuits that operated at more conventional system temperatures the new, lower-temperature heating circuits If we take the church, for example. At the moment, there are slimline radiators behind panels; the panels are being retained, so were using highly engineered aluminium radiators, which incorporate a little fan to assist the heat transfer from them, says Gustafsson. Its the same technology, its just that the bit you dont see is better engineered. The three heat pumps are sized to meet the total load. There is no additional capacity because the system incorporates a level of resilience. In the event of a heatpump failure, a maximum of one-third of peak load will be lost. In the majority of situations, there will still be enough capacity to sustain a reasonable level of service for a period of time, while the main plant is repaired or replaced, says Gustafsson. In addition, each individual heat pump has inherent resilience because it has two compressors and four fans; if a fan or a compressor fails, the heat pump is still capable of providing up to half the load. The heat pumps have three modes of operation: Heating mode, where the units extract heat from ambient air Cooling mode, where heat is rejected to the ambient air Balanced mode, where the heat demand is equivalent to the heat removed by the cooling system. Heat removed by the cooling system is added to the heating and hot-water systems. Were using heat-recovery air source heat pumps so that we can take the heat from the places that have excess and put it into either space heating or domestic water which reduces the amount of electricity needed to keep the buildings comfortable, says Gustafsson. Were also incorporating buffer vessels to maximise the time the system will spend in balanced mode. A small additional heat pump will be installed to keep the cold-water system cold. According to Gustafsson, high temperatures are becoming an A HISTORY LESSON IN ENERGY SUPPLY In the 19th century, the Pembroke College site was the industrial heart of Cambridge when it housed a large water mill for milling grain from the surrounding farmland. Later, the site was home to the Bailey Grundy Barrett Building, headquarters of the Cambridge Electric Supply Company (now being demolished to make way for Dolby Court). Bailey Grundy The now demolished Kings Mill was powered by the river Cam power station in the city, using coal delivered by barge on the river Cam. The power station generated electricity from 1893 until nationalisation in 1947. In addition to burning coal to generate power, coal was burned to provide heat in many of the buildings, as their numerous chimneys testify. Now, will be gone, replaced by electric air source heat pumps. to house the substation will be built using bricks reclaimed from the demolition of the former increasing issue for cold-water supplies, particularly in college buildings. As water temperatures rise, the management of legionella risk becomes more onerous and the quality of service decreases. To overcome this, the scheme will include a heat pump to cool the water within Additionally, the temperature of the water throughout the system is monitored and low volumes are automatically discharged when the water in the pipework outlet, regardless of usage patterns or ambient temperature. It has the additional system to manage legionella risk. As well as designing for the present, the design team is designing for the future. Pembroke College has been in existence for hundreds of years (it was founded in to be in use for many, many years to come. To ensure Dolby Courts plantroom can accommodate the equipment it will need to meet the next energy transition whatever that will be the design team has provided it with additional space. He is already eyeing up the additional space to house a large storage battery, which will enable the college to buy grid electricity when it is cheap and store the energy generated by the sites PV installations. A battery will probably have an economic value, and will further reduce the environmental impact of the scheme, because electricity is cheap when its low carbon, Gustafsson says. Work on the scheme is set to start this month, with demolition of some of the unretained buildings. Construction is expected to start in 2022. When the heat pumps are installed, the sites next energy transition will be complete. CJ Footnote 1 Joel Gustafsson completed the design from concept to RIBA stage 3 as a partner at Max Fordham. Delivery of Dolby Court, including the technical design of the site-wide heat pumps, is being undertaken by Joel Gustafsson Consulting. Max Fordham is the services engineer on the delivery of Phase 1 buildings. 44 May 2021 www.cibsejournal.com CIBSE May 21 pp42-44 Pembroke College heat pump Supp.indd 44 23/04/2021 16:06