South West

UK’s first zero carbon school is an architectural exemplar

The new £9 million Montgomery Primary School has been designed as the UK’s first zero carbon school. Constructed by main contractors BAM and designed by NPS Exter, the school has been designed to meet PassivHaus standards.

The scheme, carried out for Devon County Council, is a demonstration project through the Zero Carbon Task Force.

The school is located in Redvers Road, Exeter and caters for 420 pupils plus a day nursery. It has been built adjacent to the original school, which was demolished once the new school was completed. The school and nursery facilities are integrated within one building, whilst further facilities include a large hall and a smaller studio that provides facilities for sport, performances and community activities. In addition, there is a catering area and classrooms that link to the associated external teaching spaces.

The external elevations of the building comprise a highly insulated concrete sandwich construction and a monopitch single ply membrane roof.

External works have included the creation of a multi use games area, external play areas, external teaching spaces and a car park. In addition, there has been extensive landscaping.

A number of challenges were presented during the project, including an extremely restrictive site and one of the worst winters on record. However, all challenges were successfully overcome and the school was completed on schedule in time for half term. This allowed the teachers to move from the old school and set up in the new building in time for the returning pupils.

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 the first PassivHaus school in the UK.

Taking the requirements of zero carbon and PassivHaus on board demanded that the a number of criteria be met including the fact that 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.

The school also had to be super insulated with all components of the building envelope insulated to a U-value below 0.15 W/m2/K. In addition the building had to be air tight with a minimal air leakage, <0.6 air changes/hour which equals an air permeability value of less than 1m3/hr/m2 @ 50 Pa.

Controlled ventilation had to be comfortable, healthy and sustainable. In terms of 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 per cent.

The zero carbon element required that all electricity is provided on-site via photovoltaics. As a result, over 1,200 sq m of PV panels have been mounted on the roof of the building. In summer, the electricity generated from the panels will be sold to the National Grid, which will in turn generate an income for the school. The robust design of the building 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 air-tightness 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 in which all the classrooms were designed as identical units that incorporate toilets, cloakrooms and stores.

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 air-tightness of the precast concrete panels means that a traditional boiler is not required; rather, the ‘body’ of the heat source is the pupils and teaching staff. The variable air volume mechanical ventilation system will also be provided with electric heater batteries in individual classrooms for extreme weather circumstances.

Arthur Tatchell, Director of Architecture at NPS, said: “We used the PassivHaus principles to design the building because this is a well known, well respected, measurable method. We are now in the process of having the building accredited and expect to receive our certification in December 2011. The PassivHaus system was also a significant step in achieving a zero carbon rating.”

“The insulation in the building is massive and the standard of air-tightness around windows and doors is so high that the company who came in to test it had to run the test twice as they did not believe the result. They said that it is the most airtight building they have ever measured.”

Solar Sense

A 167.79 kWp solar PV array was installed at the new Montgomery Primary School by Solarsense UK Ltd, the South West’s leading solar company.

 Comprising 714 Sanyo 235Wp solar modules and nine SMA Sunny Tripower 17000TL inverters, the array is split over the purpose-built South-facing roof and a second flat roof, using an A-frame mounting system.

It was specified to meet the school’s entire annual electricity requirements, and is a major contributing factor to the carbon neutrality of the building. With a predicted annual energy yield of 167,873 kWh, the solar alone will save approximately 148,708 kg of CO2 every year.

 

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