HAYBRIDGE HIGH SCHOOL - CASE STUDY
Increases in education funding from central government have started to translate into work on site for school extension, refurbishment and new-build projects. Designers are having to react to a new set of drivers - the increased use of Information and Communications Technology (ICT), the onerous acoustic demands of Building Bulletin 93, and the increasing desire for sustainable and environmentally responsible designs.
Typical of many school refurbishment and extension projects is the Haybridge High School enlargement project in Hagley, for Worcestershire County Council. The project comprises a new central administration building and additional teaching accommodation to house two extra year groups.
All 18 classrooms in the new three-storey teaching block are naturally ventilated by a passive stack system. Vertical shafts have been integrated into the building design, capped with proprietary louvred terminals. A motorized damper at the base of each shaft and electric actuators on the perimeter windows enable the system to be operated automatically by the building-management system, although a manual override facility is provided in each room. This is an unusually quiet site and so the natural ventilation system does not require any acoustic attenuation to comply with the requirements of BB93. However, many school sites would have required the opening windows to be attenuated, which might have reduced the cost effectiveness of natural ventilation to below that of a well-designed mechanical ventilation system.
The ICT suite in the new central administration building accommodates 120 students and as many PCs. This density of heat gains means a natural ventilation system would have been unable to control the temperature. Mechanical cooling is required, and this will be provided by a groundcoupled heat-pump system, avoiding the need for a noisy, unsightly external heat-rejection plant, and generating cooling very efficiently. Ten 75m-deep boreholes will be sunk beneath the new hard-play area and water circulated down them in plastic pipework. Four reversible heat pumps in the plant room will produce chilled water and use the ground loops to reject heat. When cooling loads are lower, some of these pumps can be used as a heat source.
Heat to the majority of the new buildings is provided by underfloor heating. The relatively low water temperatures (40-50ºC) required by such a system make it the ideal companion for ground-coupled heat pumps, which are much more efficient when their is a small difference between ground temperature and heating flow temperature.
The low temperatures also allow the condensing boiler, which is provided as a supplementary heat source, to operate at its optimum efficiency.
Underfloor heating requires careful consideration of the build-up of the floor construction to accommodate the network of plastic pipework and insulation, and of the coordination of the pipework with any other services recessed into the floor screed (such as electrical floor boxes) and any points of high structural load. The system avoids the need for visible heat emitters such as radiators or convectors within the space - which demand maintenance and are susceptible to vandalism - but it does require some space to be made available to accommodate the pipework manifolds which typically serve a group of four classrooms.
As ICT use in schools increases further, perhaps even to the point of a PC on every desk in every classroom, architects and services engineers will have to give ever closer attention to the design of school buildings to ensure cooling loads are minimised and the design of cooling systems minimises energy use.