CIBSE AWARD WINNER | INSTITUTE OF PHYSICS reducing the number of times the heat pump needs to cycle on and off, improving its performance and lifespan. The heat exchangers improved thermal performance enables the depth of borehole required for the IOPs new headquarters to be reduced from 200m (for a conventional thermal pile system) to just 75m, saving on drilling time and cost. This was an extremely constrained site in which to drill 10 boreholes, but the system meant the drilling for each borehole could be limited to one day, as opposed to up to the two days it would have taken for a conventional system, says Edmondson. The ground source heat pump (GSHP) supplies heating and cooling to the building via underoor air handling units (AHUs) and perimeter trench heaters. LIGHTING PHYSICS In addition to providing a ventilation path, the atrium allows daylight to ood the oor plates to help minimise the need for articial lighting. Its a huge north light that allows daylight to ood the building, says Edmondson. The lighting system includes addressable and dimmable controls, and the lighting was modelled using dynamic analysis to ensure optimum illumination with minimum luminaires. The controls ensure light levels are lowered when spaces are unoccupied, to help save energy. The atrium design minimises the need for articial lighting In spring and autumn, the building has been designed to maintain comfort conditions using fresh air alone when conditions allow, with what Edmondson describes as an oversized ventilation system to maximise free cooling during the shoulder seasons. Outside air is drawn into the building through rooftop intake chimneys, where it is less polluted. The chimneys catch the wind and use positive pressure to drive the air down large vertical ducts, which have been integrated into architect TateHindles design. The fresh air is distributed on each oor via an underoor plenum. This houses a mini AHU incorporating a fan and heating and cooling coils. The AHU is supplemented by a perimeter trench heating and cooling system, designed to deal with heat gains and losses at the faade. Air rises and exits the oors into a fullheight atrium, where buoyancy will cause it to rise. An AHU on the roof pulls the vitiated air from the building. A run-around coil removes useful heat and coolth, and uses it to temper the fresh air at the intakes. Cost prevented the plantroom from opening on to the lecture theatre 26 May 2020 www.cibsejournal.com CIBSE May20 pp24-26, 28 Supp Institute of Physics.indd 26 24/04/2020 15:54