Hydrocarbon chillers on the roof

Chiller
As an approach to conforming with Government policy for equipment using refrigerants, three Earthcare chillers using hydrocarbon refrigerant are craned into position on the roof of Great Minster House in Westminster.
Hydrocarbon refrigerants are used in three rooftop chillers installed at the Department for Transport Great Minster House building in Westminster. Each has a cooling duty of 127 kW. The three Earthcare EHS chillers were specified by consulting engineer Operon and installed by P&R Morson. Tony Marshall of Operon explains that they were selected for their suitability for the application and because they conformed to Government purchasing policy on equipment using refrigerants. Current policy for the Government estate is that HFCs as refrigerants ‘should be avoided wherever practicable’ and that no equipment using ozone-depleting HCFCs should be purchased. Other advantages of these chillers include the use of conventional mineral oils, eliminating the higher risk of leakage from gaskets and shaft seals when using synthetic ester oils. Four key steps have been taken to maximise energy efficiency. Their combined effect is to more than halve energy consumption for chillers that operate all year, compared with chillers without these features. First, hydrocarbon refrigerants reduce energy consumption compared with other alternatives because of their more favourable thermodynamic characteristics. Secondly, the use of a fully flooded evaporator achieves zero superheat by the application of a plate suction liquid heat exchanger with the phial of the expansion valve located downstream of the heat exchanger. The lower condensing temperature compared with R22 improves the efficiency of the internal heat exchanger. Heat is transferred between the liquid upstream of the expansion valve and the vapour upstream of the compressor, improving the COP even more Floating head pressure control allows the condensing temperature to fall as low as 20°C if ambient conditions allow, instead of the normal 40°C. Finally, at part-load, the voltage and current to the compressor motor are modulated to reduce losses in the motor core and windings. The payback on such control is typically less than 18 months.
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