Montgomery Primary School, Exeter, has been designed by Devon County Council and NPS Exeter to be the UK’s first zero carbon school built to the PassivHaus standard. The £9 million school will cater for 420 pupils plus a nursery.
NPS Exeter started from the premise that the simplest way to deliver a zero carbon design would be to build a typical school, replace the gas boiler with biomass and buy electricity via a green tariff. However, they soon determined that such an approach is unsustainable and without value. In addition, NPS Exeter wanted to produce a scheme that had a modular design approach.
The school is designed to meet the stringent PassivHaus standards, which require buildings to have extremely low energy usage whilst providing excellent comfort conditions in both winter and summer. The PassivHaus design approach has a successful track record in mainland Europe, and has been used for the construction of 25 schools in Germany and Austria. The Flemish region of Belgium has recently implemented a school building programme in which every school is to be PassivHaus certified. Montgomery Primary School is one of the first three PassivHaus-certified schools in the UK.
Taking the requirements of zero carbon and PassivHaus on board demanded that
the following be met:
- Resource lean: adoption of the PassivHaus standard set a limit of 15kWh/m2/yr for heating, compared to the current demand of between 113 and 164kWh/m2/yr for a school built to current Building Regulations.
- Super insulated: all components of the building envelope insulated to a U-value below 0.15W/m2/K.
- Airtight: minimal air leakage, <0.6 air changes/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 in again to the fresh air supply with a heat recovery rate above 80%, with air being moved from high occupancy to low occupancy spaces.
- Zero carbon: all electricity provided on-site via photovoltaics.
- Robust: the design is expected to not only pass current requirements but to meet the demands of predicted future climate to 2080.
These are tough demands that called for a construction approach that offered future-proofed long-term performance. NPS determined that the high thermal mass and airtightness of precast concrete panels formed an important part of 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.
The high thermal mass and airtightness of the precast concrete panels means that no traditional boiler is required. Rather, the ‘body’ of the ‘heat source’ are the pupils and teaching staff. The variable air volume mechanical ventilation system will also be provided with electric heater batteries to individual classrooms for extreme weather circumstances.
The new Montgomery Primary School is built alongside the existing 1920s school, which will then be demolished. Montgomery Primary School is a building that combines 21st century design and construction to provide an enhanced teaching and learning environment.