Book - School of Science and Technology

Air-to-air heat exchangers 513Water spraysHeatexchangerHumid exhaust airExhaust fanCooled airto roomReturn airPumpSupply fanMotorFiltersHot dryoutside airFigure 17.36 Indirect evaporative coolerincrease in humidity associated with the adiabatic cooling process; some early developmentworkwas undertaken at the Department of Engineering Science, Oxford University.In the indirect system the exhaust air is cooled adiabatically using a water wash and isused in an air-to-air heat exchanger to cool the incoming air in summer.An example of the heat exchanger configuration is shown in Figure 17.36, from which itwill be apparent that the unit may also be used in winter as a `dry' heat exchanger to heatthe incoming air. The application of this type of unit is likely to be limited to overseasclimates. The riskof Legionnaires' disease must also be considered.