Book - School of Science and Technology

556 Refrigeration: water chillers and heat pumpsFor the type of commercial building to which central heat recovery systems are applied,there is commonly a heat surplus over the 24 hours of operation and some means ofstoring the excess, when available, for those hours when a deficit occurs is thus needed.Heavily insulated water vessels may meet this need and could, in turn, be `topped up' byimmersion heaters or pipe coils from a boiler plant if necessary. Figure 19.20(e) shows oneform of the finally developed system, including automatic control valves, circulatingpumps, etc.Use of multiple machinesIn the case of larger scale projects, not all of the refrigeration plant provided for waterchilling purposes would necessarily be equipped with double bundle condensers and usedfor energy recovery purposes; selection would depend upon circumstances. Taking, forexample, a building with which the authors were concerned, the total capacity of thecooling plant was 11.4 MW but only one of the three centrigual machines was used forheat recovery purposes. The equipment chosen produced chilled water at 5.6 C fromreturn at 12.8 C and condenser water was made available at 41.5 C from return at32.2 C. The power input was approximately 850 kW.Figure 19.21 shows a typical arrangement of plant that may be developed for a largescale installation.Cooling towersStandardcondenserPumpsPumpsPumpsDouble bundlecondenserWater chillingmachinesPumpsPumpsPumpsHeat storeOuter zonesPumpsPumpsCore zonesHeat exchangersPumpsTo HWS plantPumpsPumpsTo radiatorsBoilersFigure 19.21 Arrangement of central plant heat recovery