PASSIVHAUS | MAX FORDHAM HOUSE Max Fordham House 1 Rainwater absorbed into porous material on blue roof, and drained to lower roof and patio 2Rainwater absorbed into porous attenuation volume beneath patio 3 First-stage air source heat pump on south-facing terrace 4 Hot refrigerant gas is pumped to second-stage heat pump 5 Second-stage heat pump in house heats one days supply of DHW 6 DHW distributed radially to showers 7 Cold, fresh air brought into building from beneath undercroft 8 Heat is recovered from stale, moist exhaust air at MVHR unit 9 Fresh, tempered air supplied to inhabited rooms at high speed 10 Warm, moist air extracted from kitchens and bathrooms 11 Cold, moist, stale air is exhausted at high speed 12Recirculating cooker hood extracts smells, not heat 13 Well-insulated envelope, with airtightness moisture-tightness layers 14 Insulated, actuated window shutters close at night, reducing heat loss 15 Windows open fully to purge ventilate 16 Thermally massive structure allows better use of incidental heat gain in winter, and absorbs daytime heat in warm weather 17 Upper roof is used for PV electricity generation summer months. The windows can also be slightly open with the glossy and reflective shutters closed. Water supply Domestic hot water (DHW) is the largest energy demand in the house. Although solar thermal technology was considered, heat pump technology aligns well with the continuing decarbonisation of the national electricity Grid. A two-stage air source heat pump with an integrated DHW tank supplies the high-grade heat needed, and uses naturally renewed air as its heat source. While some summertime efficiency may be sacrificed in the second compressor, this is compensated by the high wintertime efficiency, and the lack of immersion heating needed. The heat pump works in tandem with the MVHR system that is fitted throughout. The heat pumps air-side heat exchanger is located within a suntrap on a south-facing terrace, and operates for an hour each afternoon, when air temperature is warmest and the heat pump is most efficient. This is also when the roof PV array is likely to be at its most productive. Hot refrigerant gas is pumped indoors to the second-stage heat pump, which heats one days supply of domestic hot water, distributed radially to showers. The second circuit takes heat at about 45oC and boosts it to 65oC. Shaw says radial DHW distribution is used to avoid recirculating domestic hot water. The cylinder is located very close to the showers and the kitchen sink, and the pipe sizes are kept small, so draw-off times are quick. The nature of the house means wed expect high turnover through all the branches. Meanwhile, DHW is generally stored at 60oC rather than 50oC with weekly pasteurisation which drove the selection of a two-stage heat pump that produces 65oC DHW fairly efficiently, says Shaw. HVAC Cold fresh air is brought into the building from beneath the car undercroft. Heat is recovered from stale, moist exhaust air at the MVHR unit, and fresh, tempered air is supplied silently to inhabited rooms at high speed through 3D-printed jet nozzles. Warm, moist air is extracted from kitchens and bathrooms, and cold stale air is exhausted at high speed. Roof engineering Planning was awarded for the home to be slightly higher than its neighbours, which maximises the effectiveness of the 5kW roofmounted solar panel array, generating around 4,000kWh annually, almost all the energy needed for the house. Rainwater is attenuated in the green roof and planters, absorbed into porous material, and drained to the lower roof and patio at a controlled rate. It is then absorbed into an attenuation volume below the patio, before being slowly drained away. A rooftop copse of hazel plants on the first floor also contributes to the biodiversity. Max Fordham House won the RIBA London Sustainability Award 2019, a RIBA London Award and is shortlisted for the RIBA House of the Year 2019. And, this winter, it will undergo its biggest test keeping its occupants warm without heating. CJ 36 September 2019 www.cibsejournal.com CIBSE Sep19 pp34-36 Max Fordham House.indd 36 23/08/2019 16:31