Carrier has supplied three high performance screw chillers for the pioneering refurbishment project at PwC’s headquarters at 1 Embankment Place, London.
The Carrier AquaEdge™ 23XRV chillers have helped the building achieve what is believed to be the highest-ever Building Research Establishment Environmental Assessment Method (BREEAM) rating for both new-build and existing buildings.
PwC selected Carrier chillers to achieve optimal energy-efficiency and achieve a high BREEAM rating to comply with its corporate environmental policy. Following the project, the nine-storey, 42,000sq m commercial office building scored a 96 out of a maximum of 100, giving it an equivalent BREEAM rating of Outstanding.
The building services solution, designed by consultant ChapmanBDSP Limited, is based on a biofuel-powered combined cooling, heating and power (CCHP) plant.
Cooling is supplied by three Carrier AquaEdge™ 23XRV 1.4MW water-cooled inverter screw chillers and adsorption units by another manufacturer.
The Carrier chillers, equipped with Greenspeed® Intelligence, were selected for their high cooling capacity, compact footprint and exceptional energy-efficiency. With a SEER rating in excess of 10.0, they are among the most efficient chillers in the world.
To provide resilience, the chillers are sized to allow two machines to meet the anticipated total load for the building, enabling one machine to remain on standby. They also provide full back-up in case the CCHP plant has to be taken offline for maintenance.
Chilled water is used to cool the building via chilled beams, with boilers providing heating to augment the low grade hot water circuit from the CCHP system. In addition, high quality comfort conditions are supported throughout the building with a combination of air handing units and fan coil units.
Carrier’s AquaEdge™ 23XRV chiller was the world’s first integrated variable speed, water-cooled screw chiller. Andrew Keogh, Carrier’s UK Technical Director, says: “The compressors are based on a tri-rotor screw design, rather than the conventional twin-rotor. This is important as a tri-rotor delivers a much more balanced compression process, enabling tighter tolerances to be maintained. The result is lower parasitic losses and better overall efficiency.”
He added: “The chillers are also water-cooled, somewhat unusual for the UK as most installations opt for air-cooled systems. The benefit of water-cooled designs is that a much higher capacity can be achieved for a given external plant footprint; plus, being based on an evaporative process, they are inherently more efficient. This, together with use of variable speed tri-rotor screw compressors, results in the system’s exceptional efficiency and performance.”
Other features of the chillers include use of an integrated hermetic compressor motor, coupled with a refrigerant-cooled variable frequency drive. The start-up current is therefore very low, protecting the building from power supply fluctuations.
The AquaEdge™ 23XRV chiller is designed to be easy to maintain and service, with built-in diagnostic capabilities for quick troubleshooting. There is also a password-protected service menu, giving access to historical alarm and alert files, enabling detailed analysis of performance over time.