The heat pump can also provide top-up for the hot water storage.The GSHP storage is sized at 200 litres to prevent the GSHP from modulating unduly.
Standard radiators, sized for a 45C flow, have been used for space heating. Decoupling space heating from air supply allows the mechanical ventilation to be turned off, reducing electricity consumption.
Islington provided 50 per cent funding for 116 m2 of grid-connected photovoltaics rated at 18 kWp. The building has limited need for hot water, so the solar thermal system is a modest single 3 kW panel connected to a 300 litre tank.
A rainwater harvesting tank will collect water from two small green roofs over the extension, and the roof of the main hall. The water will be used for garden irrigation and WC flushing respectively.
Electric lighting relies on a mixture of conventional T5 and compact low energy fluorescents. Daylight dimming controls and presence detection has been used where applicable. Large motorised south-facing roof-lights have been used to get daylight into the main hall and for summer night-purging.
The design team has paid specific attention to lighting controls, opting for a simple manual on, and auto and manual off approach. This is based on the principle of PIR-based absence detection rather than presence detection.
The existing building was consuming 581 kWh/m2 per annum. Using the Passivhaus Planning Package, it was calculated that fabric improvements will reduce the energy demand to 127 kWh/m2 per annum, of which the heating demand will be 11 kWh/m2 per annum. The energy costs are anticipated to fall from £10 710 per annum to around £600 per annum.
The building will be certified by the Passivhaus Institute, and exceeds all Part L requirements. Using SBEM, the target emissions rate was calculated at 18.8 kgCO2/m2 per annum, with the as-designed building emissions rate set at 13.7 kgCO2/m2 per annum, an 87.5 per cent improvement on the old building.
The building's main energy end-uses break down as 15 kWh/m2 per annum for the heat pump, 0000 kWh/m2 per annum for the MVHR, and 0000 kWh/m2 per annum for all lighting. The solar panel is estimated to deliver 1341 kWh per annum, and the photovoltaics 14 400 kWh per annum.
With an eye to monitoring the performance of the building under the Technology Strategy Board's Building Performance Evaluation programme (BPE), the designers have installed flow heaters onto pipework, and are considering installing a wireless datalogger so the building's energy performance can be monitored remotely.
Sub-metering is extensive but not over-complicated. There are submeters serving the ground floor and basement lighting, and the first floor lighting. The photovoltaics, air handling unit, heat pump compressor, top-up immersion heater for the heat pump, rainwater and sewage pumps also have sub-meters.
The design team is aware that the mechanical ventilation system might be slightly too complicated for a building with many different zones, such as the offices, meeting rooms, catering kitchen and basement music recording studios. They thought hard about different planned activities through the week in different rooms to get a feel for what airflow rates would be needed.
The operating set point was based on higher rates for offices occupied all day, but fairly low densities and fairly intermittent occupancy for the community spaces. Average occupancy may be between 15-25 people, but the building's refurbishment and increased usable space will inevitably see greater hours of use and more people using it.
For a building with no on-site premises management, the user controls will need to be intuitive to use and well labelled. Highly visible information panels will be provided to help educate the building's users. There will also be a familiarisation programme for all building users.
Funding from the Technology Strategy Board will be used to monitor and evaluate the certified Passivhaus refurbishment. The air tightness value of 0.43 is exemplary. It may lead to useful guidance on specialist contractor training, construction drawings, and the design and installation of thermally and air-tight junctions.
Independent comparison and analysis of forecasted energy use (broken down by end use) will be compared with actual and predicted hours of operation using the CIBSE TM22 energy assessment method. Analysis of the Soft Landings handover, with training and long-term support by the professional team, will also be assessed.
BSRIA is part of the Mayville BPE project research team and will be reporting periodically on the building's performance.
BSRIA provides independent building performance evaluations and Soft Landings consultancy. For more details email firstname.lastname@example.org or phone us on 01344 465600.
The Technology Strategy Board is a business-led executive non-departmental public body, established by the Government. Its role is to promote and support research into, and development and exploitation of, technology and innovation for the benefit of UK business, in order to increase economic growth and improve the quality of life. It is sponsored by the Department for Business, Innovation and Skills (BIS). T: 01793 442700 www.innovateuk.org.