As detail designer for building services, we had to reconcile the fiercely competing demands of environmental performance and player and spectator comfort. This challenge was completed within an incredibly tight schedule. The stadium had to be ready for an exhibition match only six months after we were appointed to work with the design and build contractor.
High performance shading
Pitch and stands are shaded from the sun by a domed roof canopy. Its steel frame is clad with hundreds of triangular panels. The concept designer intended these should be fabricated from aluminium with foam insulation on the underside to minimise radiation of heat into the stadium. We re-engineered the cladding to improve environmental performance while reducing construction time and cost.
We made the case for using a sophisticated PVC fabric instead of aluminium. It could be manufactured faster, which suited the very demanding construction programme, and it performed better. The fabric is engineered to reflect solar energy back into space and limit reradiation of heat. Because it weighs less than aluminium, using the fabric enabled savings on the steel supporting structure. In addition, it is durable and easy to maintain, and can be recycled economically at the end of its working life.
200% efficiency improvement
The stadium’s cooling requirements are met by harnessing the power of the sun. Adjacent to the stadium, mirrors focus solar heat on four water-filled tubes. The tubes are pressurised to 16 bar which means that the water can be heated to 200°C without turning to steam. This super-heated water is the driving force in the stadium’s absorption cooling system.
Absorption cooling works like this: Cold water is put into a vacuum chamber. The very low pressure causes the water to evaporate, creating a cooling effect. Cooling is transferred to a circuit of water-fi lled pipes coiled around the vacuum chamber, chilling it to 7°C. This water is circulated to provide cooling for the stadium. Meanwhile, vapour from the vacuum chamber is absorbed into a lithium bromide salt solution. The lithium bromide has to be regenerated to remain effective. This is achieved by heating it to boil off absorbed water. It is the solar-heated water that provides the energy for this crucial final phase.
Detailed design of the solar heating and absorption cooling arrangement provided outstanding efficiency. Absorption cooling systems typically deliver 0.7kW-1kW of cooling per 1kW of thermal energy. The showcase stadium delivers an impressive 1.4kW of cooling per 1kW of heat from the sun.
Recovering 76% of thermal energy
Chilled water is fed to two bespoke air handling units (AHUs) that control the stadium’s internal temperature. One supplies conditioned air to ‘back of house’ offices and hospitality facilities. The other serves the pitch and grandstand. To achieve the required cooling with minimum energy loss, there are two thermal wheels in each AHU. The wheels link the exhaust air and supply air streams, transferring thermal energy between the two as they rotate.
On the hottest days, fresh air enters the stadium’s AHUs at 50°C. It is cooled to 30°C by the first thermal wheel, which recovers 76% of the cool from the outgoing air stream. Supply air has to be dehumidified and this is where the chilled water plays its part. Coming into contact with pipework carrying the 7°C water supply, water vapour condenses out of the air stream. After dehumidification the air stream is 15.5°C – too cold for spectator comfort. So the second thermal wheel extracts heat from the exhaust air stream to raise the temperature of incoming air to 18°C.