CASE STUDY | BURRELL COLLECTION The flat roof was the other major fabric element targeted for improvement. Resistance tests showed its average U-value to be around 2.2-2.3W.m-2.K-1. The old roof was removed, and replaced with a new, highly insulated construction, originally specified with PIR insulation, which gave a U-value of 0.18W.m-2.K-1. After the fire at Grenfell Tower, however, the PIR was ditched in favour of noncombustible mineral wool at the clients request. This increased the roofs U-value slightly, to 0.25W.m-2.K-1, which, Cameron points out, still delivers an 80-odd per cent improvement. The new roof also supports 384 photovoltaic (PV) panels generating up to 140kW electricity. To make the most of these panels, a 250kWh battery is being installed so that electricity generated by the PVs can be stored when the building doesnt need the energy. Electricity can also be taken from the Grid when tariffs are low and stored for use in charging the parks electric buses. Improvements have reduced the building s peak heat load by about 50% and its cooling demand by at least 20% The services solution An all-air system, based on eight main air handling units (AHUs), is housed in a sub-basement in the middle of the building. This provides the bulk of the heating and cooling to the galleries and other spaces. Internal conditions in the galleries must be maintained between 20C and 23C and 40-60% RH to comply with the insurance requirements for the exhibits. In total, the AHUs move between 60,000 and 80,000 litres of air a second. While they provide fresh air for the occupants, about 90% of the air is recirculated via an integral mixing box. At night, when the museum is unoccupied, the system is designed to operate on full recirculation. Covid hit just when we had started to design the air handling system, which Gallery temperatures are being kept at a constant 21C initially ARUP IMPLEMENTING CIRCULAR PRINCIPLES WITH GLASS RECYCLING Arup, the projects faade consultant, found that elements of the original glazing due to be replaced could be reused for architectural glass production. As a result, more than 16 tonnes of glass was recovered for processing into new architectural glass, saving CO2 by eliminating the need to extract new material. Body-tinted, laminated and large-scale glass units that could not be recycled were processed into other building products under a new glass industry network of manufacturers, research institutions and end-of-life/recycling facilities. Arup claims that no glass material removed from the building was sent to landfill. More than 4.5km of glazing frames were also reused through what Arup describes as a painstaking process of detailed inspection, structural calculation, cleaning, repair and strengthening of fixings to support the new high-performance glazing units. The frames refurbishment involved the addition of new thermal breaks and the use of a bespoke gasket system. The frames re-use reportedly saved 8.5 tonnes of aluminium. called into question the fact that we are recirculating air, says Cameron. But if you dont recirculate air, you might as well shut down the museum because its energy bills will be through the roof. Fresh air quantities are controlled by CO2 sensors. Because the building is relatively open plan, the AHUs mix fresh air into the recirculated air supply to all zones served by the unit. A thermal wheel transfers heat and coolth from the exhaust air stream to temper the incoming fresh air. When cooling is required this is then cooled and dehumidified using chilled water supplied by two 300kW high-performance heat pump chillers, which recover heat from the cooling cycle. The outdoor air is then mixed with the recirculated air in the AHU and reheated as necessary by the primary heating coil. Primary coils run at a temperature of 4060C using the chiller-recovered heat. If we need to boost the temperature further, the boilers can kick in; they can also boost to 80C-60C but, so far, that high temperature demand has never materialised, says Cameron. With all coils and heat emitters sized for 40-60C, the infrastructure has been developed to allow for full heat pump changeover in the future. Unusually for a museum, the Burrell has a significant amount of south- and eastfacing glass, plus an equally significant area of north-facing glazing. I know this is in 32 October 2022 www.cibsejournal.com CIBSE Oct 22 pp30-33 Burrell Collection.indd 32 26/09/2022 17:50