NPS, Devon County Council and Exeter University worked in partnership to deliver Montgomery Primary School - the UK’s first Passivhaus cerrtified and zero carbon in use primary school.
The 420 place primary (plus nursery) school was built and accredited to PassivHaus standards,therefore the following requirements had to be met:
Resource Lean – adoption of the Passivhaus standard set a limit of 15 kWh/m2/yr for heating (compared to the current demand of between 113 – 164 kWh/m2/yr for a school built to current building regulations)
Super insulated – all components of the building envelope insulated to a U-value below 0.15 W/m2/K
Air tight – minimal air leakage (<0.6 air changes/house/volume/hour which equals an air permeability value of less than 1m3/hr/m2 @ 50 Pa)
Controlled ventilation – comfortable, healthy and sustainable
Heat recovery – the major part of the warmth from exhaust air is fed again to the fresh air supply with a heat recovery rate above 80 per cent with air being moved from high occupancy spaces to low occupancy ones
Zero carbon – all electricity provided on-site via photovoltaics
Robust – the design not only passes current requirements but also meets the demands of future climate to 2080.
These tough demands called for a construction approach which offered future-proofed long-term performance.
NPS was determined that the high thermal mass of air tightness provided by precast concrete panels offered the solution. In order to increase the cost-effectiveness and buildability of precast prefabrication, a modular approach was developed where all the classrooms were designed as identical units incorporating toilets, cloakrooms and stores between. This also allowed the provision of a draught lobby to maintain air temperature and control air leakage whilst providing direct access to outside.
Given the level of airtightness, no traditional boiler was required, with the ‘body’ of the ‘heat source’ being the occupants. A mechanical ventilation system with trace heaters is provided to individual classrooms for extreme weather circumstances.
Among the challenges and constraints the design team overcame was the location, being on a flood plain and the very tight site is surrounded by high density housing and narrow roads. The existing school remained occupied during construction.