Innovation: Energy saving office has air of a cathedral: Window opens on controlled environment

AN OFFICE block that will use 45 per cent less energy and produce 23 per cent less carbon dioxide than comparable buildings is nearing completion in Cambridge.

The headquarters of the recently established telecoms company Ionica represents a new approach to heating and air-conditioning in multistorey buildings.

Breaking with the current tradition of sealing buildings as the easiest way of controlling the internal environment, staff will be able to open the windows, and natural air movement will be harnessed in the heating/cooling system.

Sealing buildings uses a lot of energy, and buildings account for approximately 50 per cent of energy use in Europe.

The consulting engineers on the project also claim the design could mark the end of 'sick-building syndrome'.

The key to the heating and cooling of the building is in the use of standard hollow flooring slabs, which act as channels for air and create a thermal mass that can retain either heat or cold depending on the season. Air is drawn down from the roof and introduced at each level through vents in the floor. When the building needs to be cooled in summer, air is taken in at night, and circulated through the channels in the hollow slabs.

The slabs themselves are also cooled by the air, and retain their cooling influence during the day, imitating a cave or a cathedral, which stay cool even on the hottest summer days because the stone acts as a heat sink, drawing in heat and keeping the air cool.

During the day, windows can be opened for ventilation, and air circulation is encouraged by an atrium in the centre of the building with wind towers at the top - through which the warm air inside the building can rise and be expelled. The system creates cross-currents in the same way as opening two windows at home causes a through draught.

For most of the year, there will be no need for mechanical cooling or heating of the building, but on very hot days incoming air is mechanically cooled and window blinds and canopies also protect the interior from the sun.

In winter, a combination of solar power and mechanical heating warms the incoming air. This passes through the hollow slabs, creating warmth in the slab mass, and is circulated through the floor vents. Separate heaters in the offices supplement this if necessary, but the need for extra heating is minimised by highly insulated walls and by special glazing.

A computer-controlled weather station on the roof reacts to internal and external temperatures to control the internal environment.

'If people know they can open the windows, they will tolerate a greater range of temperatures,' says Guy Battle, a partner at environmental consultants Battle McCarthy who worked in partnership with the building services engineers, Rybka Smith Ginsler & Battle, on the building's design.

'In a sealed box with tinted windows, people expect the temperature to be 22C, plus or minus one degree. But bodies actually adapt to the seasons and - given the right cues - people's perception of hot and cold changes, especially if they are able to control their environment.' The temperature in the Ionica building will be allowed to rise to 25C.

Although the evidence seems to indicate there is no such thing as a 'sick building', Mr Battle says the Ionica design does away with factors that have been implicated in sick-building syndrome, including sealed buildings, tinted glazing and heating and cooling systems that cannot be controlled by staff.

In traditional artificially lit buildings, lighting accounts for about 30 per cent of energy consumption. The glazed central atrium means that much of the Ionica building can be illuminated by daylight, bringing a 50 per cent saving in the use of electricity for lighting.

Opening the windows could cause a noise problem. A survey by Cambridge Architectural Research showed the noise levels on the northern facade to be on the limit with windows open.

However, psychology will play its part again. Trees will obscure the view of the traffic and so reduce 'perceived' noise.

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