Portfolio - Pontprennau Primary School
To design a low energy standard school capable of being constructed within the confines of a conventional building budget required an extremely efficient and cost-effective design solution. The low energy strategy informed and influenced many of Howard Doolan Associates decisions about the building's servicing strategies.
A low energy solution was developed using IES dynamic thermal simulation analysis software. Knowing that we had an airtight, energy efficient building envelope enabled us to develop an elegant, simple ventilation strategy. Natural ventilation alone can keep the building comfortable. Within the building high level windows open to allow warmed air to escape to outside. The escaping air pulls in fresh air from the classrooms. Manually openable windows in the classrooms ensure sufficient ventilation to maintain comfortable conditions.
The windows can be opened or closed by the teacher using an electronic actuator to control ventilation. This interconnected system of high level openings allows secure ventilation and enables the system to be used at night to pre-cool the building in hot weather. This solution eliminates the need for mechanical cooling, while providing high levels of fresh air.
Because the building's main assembly hall is occupied intermittently and the occupancy can vary from one class of 30 to all 420 pupils for school assembly, this room is fitted with a CO2 sensor and roof mounted natural ventilation units. When the CO2 sensor calls for fresh air, the units draw air into the room from outside. When the sensor detects the hall is empty, the unit closes to stop the system supplying fresh air to an empty room.
Modelling and analysis of the occupied spaces demonstrated that the scheme complied with the ventilation and overheating recommendation of Building Bulletin 101: Ventilation of School Buildings which states that the air temperature in occupied spaces should not exceed 28°C for more than 120 occupied hours a year. In fact, modelling predicted that the maximum time any space would exceed 28°C was 35 hours a year, well within target.
To meet the heat demand the school is fitted with an underfloor heating system run at low temperature, system fed from a pair of condensing boilers. This warms the classrooms while enabling the boilers to run in full condensing mode. The heating circuit has a high temperature differential, typically 50°C flow 30°C return, to keep flow rates to a minimum. All heating pipework is highly insulated to prevent uncontrolled heat loss.
In addition to reducing energy consumption in the designed Mechanical Services Howard Doolan Associates also set about minimising lighting and ICT loads. The form of the building ensured that most spaces have high residual light levels to minimise the need for artificial lighting. When light is needed it is supplied from low energy LED lamps and fittings. These are controlled automatically to suit the required lighting levels in terms of available natural daylight and occupancy. Presence detection ensures lights will turn off when rooms are empty.
In addition 55 m2 of PV array supplements the electrical usage of the building further reducing the already excellent carbon footprint of the proposed building