Book - School of Science and Technology

Other systems 399Fan SectionFiltered returnair intakeCoolingcoilsElectricalheaterControlpanelHumidifierCompressorsFigure 14.25 Typical down-flow type room air-conditioning unitRoom coolersThis heading covers a separate field in that such units are commonly complete in themselves,containing compressor, air filter, fan and cooling coil. Electric resistance heatersmay be incorporated for winter use and, rarely, means for humidification. Fresh air may beintroduced if required. Being of unit construction, alternatively described as packaged,they are not purpose-made to suit any single application and thus may well be economicalin first cost. In some cases, a so-called `split type' of unit may be found where the condenserand compressor are mounted remotely from that part of the equipment which serves theroom concerned. Bulk and noise at the point of use are thus much reduced.Units of small size generally have the condenser of the refrigerator air cooled, but inlarger sizes the condenser may be water cooled in which case water piping connections arerequired. Apart from this, the only services needed are an electric supply and a connectionto drain to conduct away any moisture condensed out of the atmosphere during dehumidification.Compressors in most units are nowhermetic and are therefore relativelyquiet in running.Sizes vary from small units suitable for a single room, sometimes mounted under awindow or in a cabinet, similar to that shown in Figure 14.25 and the range goes up tounits of considerable size suitable for industrial application, in which case ducting may beconnected for distribution.Reverse cycle heat pumpsThe heat pump principle described in Chapter 19 has been applied to general airconditioningapplications. In a similar fashion to the application of induction units and