CHILLER FIVE PANCRAS SQUARE


The pump selection and staging has also been addressed to provide effective operation to reduce energy consumption and reduce the end-user’s running costs


than the 2010 Building Regulation target. High effi ciency targets were set by the


design team, and to achieve them, the focus was put on innovation. The main items identifi ed were: chillers and chilled water auxiliary equipment; air-handling units and exhaust fans; lighting control and luminaire selection; and power distribution, including metering and sub-section pre-wired and pre-tested off-site. The CIBSE Journal will publish a full case


study on Five Pancras Square on completion, but this article focuses on the chiller, which M&E contractor Kier IME says is key to the building achieving – and exceeding – design performance targets. The Part-L compliance dynamic thermal model set a seasonal energy effi ciency ratio (SEER) target of 4.9 on a total building cooling load of 2.2MW, divided over two air-cooled chiller units. All the central plant was targeted for improvement against the energy model, with consideration given to the spatial constraints and co-ordination of a city-centre building. A chiller system from Hitachi features in the scheme. The 14 RCME modules selected each have a maximum cooling capacity of 165kW and the high-effi ciency screw chiller was shown to achieve a SEER of 5.31. The screw compressor operates on refrigerant R134A, which is associated with high part load effi ciency and reliability, and offers a three-year warranty. The RCME range achieves compressor effi ciencies similar to more expensive and complex units. Twin plate heat exchangers on each module


are designed in series for greater effi ciency, which in turn ensures the refrigerant velocity increases, plus constant distribution of the refrigerant fl ow across the exchange surface. The chillers are built from three basic


modules with ratings of 40HP, 50HP and 60HP. By combining them, higher capacity units can be achieved up to 1,280kW, with one


module set as master and the rest as slaves. All operate together as a single system. The project team looked at mixing the chiller modules and variability of the capacities to suit the minimum/nominal/maximum load, and fi nally settled on 14 x 60HP, which delivered the optimum effi ciency against the spatial constraints. If space was not a factor, then a greater number of units with a smaller output would deliver higher effi ciencies, as they could be more closely controlled to match the load. Each chiller for the King’s Cross Kier project


will be supplied with a power meter assembled at the factory. This will display total power and power per phase, frequency, power factor total, voltage both phase-to-phase and phase-to- neutral, three phases and neutral current, with an hourly counter and time-integrated outputs. Efforts have been made to stage the chiller


units down to minimal load as low as 32kW. Pump selection and staging has also been addressed to reduce energy consumption and cut the end-user’s running costs. The main pump sets run from 100% (2.2 MW) to a minimum (220kW) and the secondary pump covers the range from 15% (330kW) to 1.5% (33kW). Kier says its specifi cation of innovative systems, including the chiller, means the envisaged post-construction BREEAM score is actually expected to be higher than the design- stage score of 93.05%. The team is working towards a revised target of 96%, which would make it the most sustainable building in the UK, as assessesed by the BREEAM rating process. The building is expected to open for business in 2014, and will be closely monitored in terms of energy and water use. The effective operation of the chiller will be key to Camden achieving its expected energy savings, and crucial in ensuring taxpayers don’t contribute towards the project’s costs. CJ


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