All-electric heating and cooling solution is heat-pump based
Underfloor heating and cooling for the three floors of this new office building in Aylesbury is served by a Calorex heat pump with an electrical input of 7 kW.
Underfloor heating and cooling served by a Calorex heat pump is providing an energy-efficient solution for a suite of offices in Aylesbury. Self-built by McBrien’s Group, which is a civil-engineering, services and development contractor, the building comprises a 97 m2 basement, 111 m2 ground floor and 66 m2 first floor. The client did not want windows or walls cluttered with split-system components, Gas was not brought onto the site, and oil and propane were ruled out due to lack of space for bulk storage. This all-electric solution is based on an air-to-water heat pump with an electrical input of 7 kW giving an average winter COP of 3.5 with an outside air temperature of 5°C. Geoff Greening of underfloor heating specialist Hypocaust of Gloucester, explains, ‘The concept was to move away from conventional split air conditioning and adopt passive design techniques with simplified controls. The structure was virtually airtight, with high thermal inertia and controlled ventilation rates to minimise energy consumption. A bespoke Hypocaust underfloor heating and passive cooling system was installed. The Calorex heat pump is sited outdoors and delivers 18 kW of heating and 16 kW of cooling. A primary pump is used between the heat pump and 250 litre thermal store, with a secondary pump to circulate water from the store and around all circuits. The thermal store prevents the heat pump from cycling and holds sufficient energy to meet periods of high demand. The 18 mm polybutylene barrier pipe is clipped to 50 mm-thick polystyrene board with high compressive strength (350 kPa). There is one manifold per floor, and each floor is sub-zoned using wireless programmable room thermostats. The pipes are encapsulated in a 50 mm calcium-sulphate screed to give high thermal conductivity.