A two classroom extension with associated toilets and cloaks area for Reception and Year One children is the basis if this project and is the first of three phases of development proposed for the site. The school governors placed a very strong emphasis on low carbon design solutions.
Engaged to perform a full design and site visiting role Worldwise Limited initially considered the available capacity of existing site utilities and boiler plant and produced a report on ways of meeting or exceeding Building Regulations Part L requirements. This initially favoured the provision of a dedicated gas-fired condensing boiler coupled to an underfloor heating system as the most economic way of satisfying regulations and the need to have low surface temperatures in all areas of the primary school. It offered the lowest capital cost solution. The second option was the use of closed loop ground source heat pumps using “slinkies” in trenches, again coupled to the underfloor heating system. However; the availability of sufficient land to run the “slinkies” was questionable and the cost of using the alternative borehole arrangement was considered excessive.
The school was not considered an appropriate site for a micro-CHP system because of the lack of continuous demand and low base electrical load relative to peak heating demand.
Wood fuelled boilers were discounted because of the lack of space for fuel storage. Active solar thermal was given consideration but ruled out because it would not meet the winter heating and hot water demands. Wind turbines were discounted because of likely problems with Planning.
Given that Planning Permission had been granted for a structure that included extensive south-facing roof areas and holding onto the optimum choice of heat producing plant and distribution system; the adoption of a photovoltaic array to provide the power to run an air-to-water heat pump was considered next. Numerous options were discussed with the architect and specialist suppliers including thin-film polymorphous cells for integration into the roof fabric but the monocrystalline “retro-fit” system won out, offering the most buildable and cost-effective solution. The 60% grant availability (50% from the Low Carbon Building Programme Phase 2 scheme and a further 10% from Dorset County Council) and some tough client decisions to trade-off architectural “niceties” in the overall building design made this a viable solution.
The system will comprise 74m2 area of PV cells producing 9.72kWp with predicted output of 7776kWh/year. Appropriate inverters, import/export metering and a large public display provided as part of the scheme. This greatly exceeds the input necessary for Part L compliance and it has been agreed with Building Regulations Inspectors that the surplus can be utilised on future development phases.
In addition to the above low carbon solutions the classrooms will be naturally cross-ventilated meeting the requirements of BB101, T5 linear and low energy fluorescent lighting is automatically controlled using photo cells and PIR movement detectors with rooflights providing good daylighting in WC and cloaks areas. Classrooms have good daylighting through a high level northlight and glazed south-facing walls. Water flow to wash basins is controlled by proximity sensors.
