Book - School of Science and Technology

546 Refrigeration: water chillers and heat pumpsAir cooledcondenserDry air coolerWater / glycolcooling coilRefrigerantD.X. coilExpansion deviceCompressorWater / glycol pipeworkRefrigerant pipework(a) Separate circuitsFigure 19.13 Free cooling using a dry coilCondenser(b) Combined circuitWhen outside ambient conditions are suitable, the compressor may be switched offand the by-pass put into use, allowing refrigerant to flow between the evaporator andcondenser. In this mode, the evaporated refrigerant from the chilled water heat exchangeris drawn up to the condenser, by pressure difference, where is condenses and returns bygravity to the evaporator. In a multi-chiller installation, using this method of operationwhen outside ambient conditions permit and with a constant cooling demand throughoutthe year, energy savings of about 50% may be achieved. The additional capital cost of theinstallation would be of the order of 20%.Refrigeration plant componentsRefrigerant pipeworkSome plant configurations will involve the design of pipeworkcarrying the refrigerantbetween components in the cycle. Special attention must be given to this important aspectof the installation because the fluid in circulation, being volatile, may be in gas or liquid formor a mixture of the two. When dealing with such design, reference should be made tospecialist works on the subject, to ensure that the essential basic criteria are met in order to:. minimise oil loss from the compressor. ensure satisfactory refrigerant flow to the evaporator. prevent liquid refrigerant or oil in slugs from entering the compressor (during operationor when inoperative). prevent oil from collecting in any part of the system. avoid excessive pressure loss. maintain the system clean and free from water