The brief for architects Feilden Clegg of Bath called for the use of natural ventilation, maximum use of daylighting, maximum use of the building's mass to moderate temperature, and controls that would let the building meet its environmental targets but keep its occupants happy. 

In addition, maximum use was to be made of recycled and waste materials and the building was to score the highest possible BREEAM rating of 'Excellent'. And it had to look good! 

The new Environmental Building at Garston has been built as a demonstration building for the Energy Efficient Office of the Future (EoF) performance specifications, drawn up by a number of companies representing the manufacturers, designers and installers of building components and the fuel utilities, as part of the EoF project run by BRECSU. 

A key part of this specification is the need to reduce energy consumption and CO₂ emissions by 30% from current best practice. Air conditioning is not used in the new building - the major energy consumer in many existing office buildings. Other savings will be made by making better use of daylighting and by using the building's 'thermal mass' to moderate temperatures. 

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The most striking feature of the building when seen from the south side is the five distinctive ventilation shafts running up the façade. These form a key part of the energy-saving natural ventilation and cooling system. 

Working rather like a greenhouse, the summer sun shines into the glass-fronted shafts, warming the air inside. This warmed air naturally rises out of the stainless steel 'chimneys' and causes air from inside the building to be drawn through to replace it. On a breezy day the movement of air across the tops of these chimneys increases this 'stack' effect. On very warm, still days low-energy fans in the tops of the stacks can be turned on to give greater airflow. 

This air moving out from the building draws cooler, fresh air in from outside through ventilation openings. On still, windless days the air is taken from the shady north side of the building, coming in through high-level windows. On warmer or windy days (when its windy the air on the north side is not as cool), air is drawn in through passages in the curved hollow concrete floor slabs. Because of its bulk - or thermal mass - the concrete cools the incoming air by absorbing heat from it. Additional cooling can be achieved by circulating cold water through the slab. Cold water is drawn from a 70 metre deep bore hole where the temperature is constantly around 10 Celsius. This is passed through heat exchangers to chill water that is circulated through underfloor pipework. The borehole water is returned to the ground via a second, shallower borehole, so no water is 'wasted'. 

Overnight, the control systems can open ventilation paths right through the concrete slab to cool it further, storing this 'coolness' for the following day. The exposed curved ceiling gives more surface area than a flat ceiling would, acting as a cool 'radiator', again providing summer cooling without energy-consuming air conditioning. 

During the winter months the water circulating through the concrete slab is heated to give gentle underfloor heating. This is supplemented when necessary by conventional radiators around the perimeter of the office area. The water is heated by condensing gas boilers which are 30% more efficient than ordinary boilers, mainly by recovering much of the heat that is usually wasted in the flue gases . 

The ventilation and heating systems are controlled by the Trend building management system (BMS), but, as with most other systems in the building, a degree of user override is provided to suit individual needs. 

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To make maximum use of available daylight the building has a large glass area, carefully optimised to provide high light levels but low heat losses and solar gain. To prevent excessive heating and glare from the sun shining in - the 'blinds down, lights on' situation common in many offices on sunny winter days - the building has a system of Colt motorised glass louvres on the south façade to control the daylighting levels. 

Each louvre has a translucent ceramic coating on the underside which obscures the direct sunshine whilst still letting diffuse light through. During the day the angle of the louvres changes according to the position of the sun. At times when direct sunshine is not a problem the louvres are angled to act as 'light shelves' - reflecting light off their smooth upper surface onto the ceilings of the offices. This reduces the amount of artificial lighting needed in the parts of the offices furthest from the windows. 

Like the other control systems in the building, the automatic control can be overridden by the occupants. By using a TV-style remote control unit, users send a signal which is picked up by a sensor in the office lighting units. This is passed through the LonWorks network to the Trend management system which operates motors on the individual louvre units. 

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The main office areas are lit using the latest generation fluorescent lights from Philips. Their new TL5 lamps use less power than previous tubes, are much slimmer allowing for new sleeker light fittings, and contain much less mercury (just 3mg per tube compared to 15mg in the previous best case). 

The light fittings themselves use advanced reflector technology to let 40% of the light shine upwards as diffuse uplighting and reflect the rest downwards to provide a good working brightness (300 lux) at the desktop level. This combination of advanced tubes and advanced optics makes the light units extremely efficient, giving an output of 104 lumens per Watt. 

This is the first installation of this new lighting type to use dimming technology. Philips 3-way 'Helio' sensors fitted into the lighting runs measure the ambient daylight levels and adjust the lamp brightness to suit. Movement detectors in the sensors turn the lights off if the local office area is not occupied. And infra-red sensors pick up signals from the hand-held remote control units used to manually adjust the lighting brightness. The same IR sensor is used to carry the instructions to override the ventilation and solar shading systems. 

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The architects' original design included a large area of cedar cladding on the south facade to the left of the main doors as an architectural feature, visually linking with the cedar-clad seminar suite at the back of the building. When funding from the Department of the Environment, Transport and the Regions was made available to part-fund a demonstration building-integrated photovoltaic array (BIPV), this was installed as a one-for-one swap. 

The array, from Intersolar Systems, uses thin film amorphous silicon cells incorporated into a glazed cladding. There is little experience of this arrangement in the UK, so this demonstration aims to find out more and report the findings back to industry. Is is hoped that in time there will be sufficient interest in BIPV arrays to allow the costs to drop to more economically competitive levels. 

The output from the cells (as direct current) is fed into the building's main supply panel via an inverter, providing additional power to the building from a non-polluting source. Inside the building a status panel shows the amount of electricity being generated, the percentage contribution to the building's lighting load, and the cumulative total since May 97 - the date of first occupation. 

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For further information about the Environmental Building please contact:
James Fisher   (01923) 664722   email fisherj@bre.co.uk
Matt Grace   (01923) 664740   email gracem@bre.co.uk