CHILLERS REFRIGERANTS
A 450KW hydrocarbon chiller undergoes pre-commissioning checks
CASE STUDY CHURCH HOUSE
Church House in London was built to commemorate Queen Victoria’s golden jubilee and hosted the fi rst meeting of the fl edgling United Nations in 1945. In 2007, a 625 kW air-cooled water chiller using the HC refrigerant R290 was installed. The long-term payback, both fi nancially and in reduced environmental impact, more than offset all the capital, installation and disruption costs. The project lifecycle cost analysis is summarized in the table on page 46.
The technical development of the system was straightforward; the most time-consuming element was optimising the selection of compressors, heat exchangers and valves for non- standard conditions. The main barriers faced in developing the technology were getting selection data for components using hydrocarbon refrigerants, and getting components CE marked.
Preferably this should be split between two sides to encourage displacement of the leaked refrigerant. The fl oor should form a basin to hold twice the volume of the refrigerant liquid; a typical depth is 100 mm. The fl oor should slope towards an extraction point. Doors should open outwards with catches designed for overpressure above 2 kPa. They should be self-closing, well fi tting, and with an appropriate fi re rating. The louvres will ensure that natural ventilation is available, even if a refrigerant release coincides with an electric power failure. In the event of a major refrigerant release, the plume from the bottom of the louvres may be fl ammable. Mixing of the plume with air outside the plant room should not be obstructed. Outside traffi c and ignition sources should not approach the louvres closer than the plant-room fl oor-to-ceiling height. Refrigerant pressure relief valves on the
chiller should connect to steel pipes, which discharge outside the building upwards and 3m clear of ignition sources, persons or property. Extraction ventilation suitable for Zone 2 applications should also be
44 CIBSE Journal June 2012
installed. Discharge to the outside of the building must be free from obstruction, suitably guarded, and located so as not to cause danger. The purpose of the ventilation is to simply expedite dispersal. However, there is no need for the 158 air changes per hour required for exemption from EU rules known as ‘ATEX’ (Appareils destinés à être utilisés en atmosphères explosives). But to be effective, at least 16 air changes per hour are needed. At least two fl ammable gas detectors
should be used per plant room, and should be far from air inlets and each other. They should be fi xed to a wall more than 300 mm above the fl oor to protect from accidental damage, and less than 600 mm to ensure detection of refrigerant vapour. Either of the fl ammable gas detectors should shut down the chiller, electrically isolate all electrical equipment except emergency lighting and extraction, activate alarms, and automatically switch on ventilation fans. The alarms should include an audible
signal and a fl ashing light, both in the machinery room and externally, so that emergency action may be initiated;
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Nicholas Cox
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