Modified AHUs provide heat rejection for chillers
A novel approach to rejecting heat from three 1 MW chillers serving a prestigious apartment development in London is based on eight Flakt Wood air-handling units with adiabatic humidification.
The design team originally proposed dry coolers on the roof, but this was rejected as not complimenting the existing streetscape of Knightsbridge.
The design team at consulting engineers Cundall suggested the approach based on air-handling units.
The chillers and the air-handling units are in an internal plant room at low level, and the local authority imposed a maximum temperature on air leaving the plant room.
Air from the plant room is drawn through the air-handling units and cooled by adiabatic humidification. This cooled air then extracts heat from heat-rejection coils serving the chillers.
For much of the year, the extra cooling effect of adiabatic cooling will not be needed. When it is required, it can reduce the air-off temperature by 8 K.
The system can also reject 1.5 MW of heat to borehole water, but there is an annual limit on the heat rejected by this means, so it is used only at peak conditions.
These AHUs are based on the EU84 model and are 4 m wide and 7 m long with a special cross section to reduce their height to 2.3 m. Each of the eight units can reject 300 kW of heat. They are stacked on top of one another, with a clearance of just 100 mm at the top of the stack.
This development of 80 apartments was designed by Richard Rogers. Its 2500 m2 penthouse is expected to sell for £100 million on completion in 2010, making it the most expensive flat in the world.