Book - School of Science and Technology

400 Air-conditioningfan-coil systems, heat pumps may be arranged in a modular configuration around thebuilding. Units that operate both as heaters and as coolers are normally installed andthese are termed reverse cycle heat pumps. Floor, ceiling and under-window types areavailable; a typical under-window unit is illustrated in Figure 14.26.Each unit incorporates a reversible refrigeration machine comprising an hermeticrefrigeration compressor, a refrigerant/room air coil, a refrigerant/water heat exchanger,a cycle reversing valve and a refrigerant expansion device. When the space requiresheating, the air coil acts as a condenser, drawing heat from a water circuit through theheat exchanger acting as an evaporator, upgraded by the compressor. When the spacedemands cooling the air coil becomes the evaporator, the heat being rejected to the watercircuit via the water-side heat exchanger acting as a condenser. Figure 14.27 illustrates thecomponents and operating cycles of such a system.Discharge grilleControlsHeating/coolingcoilsCondensate trayFansFilterReturn grillePower,condensateand waterconnectionsCompressor sectionFigure 14.26 Under-window reverse cycle heat pump unitReversingvalveReversingvalveCompressorCompressorRoomcoil(heating)Roomcoil(cooling)Refrig/waterheat exchangerExpansiondevice19ºC 27ºC 38ºC 27ºCWaterWaterFigure 14.27 Operating cycles for a reverse cycle heat pump system