Architect Percy Thomas Partnership (PTP) Engineer Hoare Lea
Client Ministry of Defence, Defence Procurement Agency
The Defence Procurement Agency is responsible for purchasing equipment for the armed services, and was originally housed in sites widely dispersed throughout the country. In 1992 the MOD took possession of a98-acre site near Bristol, with the aim of creating a totally self-sustaining office campus to house 5500 staff together with all the ancillary accommodation, to include car parking, technical library, storage, simultaneous interpretation, lecture and conference facilities, sports, training, catering and a 100 place crèche, resulting in a complex of 1.3 million sq.ft., one of the largest office developments in Europe.
The scheme design resulted from a cooperative effort between all the design disciplines, in which the following key elements were identified,
• Occupant performance
• VDT use throughout
• Energy consumption
• Life cycle costs
Although this list is not said to be in any order of priority, it is clear that the role to be played by daylighting, tied in as it is with energy, views, ventilation and occupant satisfaction was considered to be of first importance. With some 20,000 m2 of office glazing it was necessary to ensure that the elemental window design was both energy efficient and cost effective, whilst satisfying the needs of the occupants.
The type of glazing to be used was thoroughly investigated, with ten systems modelled in full annual weather conditions.
The final choice rested on a system of triple glazing, with opening lights for ventilation, providing an approximate percentage glazing of 40 per cent of the external wall area. Solar control is by internal blinds incorporated in the triple glazing. The use of external brise soleil was outweighed by their capital, maintenance and replacement costs. It was shown that 'interplane' blinds were more desirable in achieving enhanced performance and a reduction in cleaning.
The type of glass used was 'clear,' designed to enhance the importance of the view out; which also reduced the contrast between open and closed windows; and whilst some of the high tech glasses, such as specialist coated or tinted glass, were investigated, it was felt that their long term viability had not been sufficiently established.
The section through atypical four-storey office block with its central street shows that no-one is more than 6.5 m away from a
window, and the impression within the offices is one of natural light.
The quantity of daylight available is automatically linked to the level of artificial lighting by the use of'intelligent' light fittings, allowing considerable savings in electricity, and a consequent reduction in CO2 production. Using 350 lux as a standard, it has been established that on average only 36 per cent of the artificial lighting is required during the day. The installed load is I6watts/m2.
Plan of atypical neighbourhood
Interior of daylit cafe
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