Book - School of Science and Technology

Refrigeration plant components 553Drift eliminatorsSpray nozzlescoil connectionsHeat exchangercoilAccessTowerrecirculationWater make-upOverflowFanDrainImmersion heaterbleed valveMotorWaterrecirculationpumpFigure 19.19 Closed circuit water coolerwhere the cooler is below the level of the refrigerating apparatus; or where the cooler isused to provide `free cooling'. Due to the additional heat exchange inherent in thecircuit and consequent loss of efficiency, this type of tower tends to be relatively large insize.Regardless of the type of evaporative cooler, its location must be carefully selected suchthat the air discharge, which could be contaminated, is not carried into air intakes, or intoopenable windows, or across public access routes. A high quality of maintenance isessential with such cooling devices and provision must be incorporated for inspection,maintenance, cleaning, water treatment and taking water samples, registration with localauthorities may also be required. To reduce the quantity of water droplets carried fromevaporative coolers, eliminator plates should be fitted at the air discharge position.Rating of cooling towersThe heat to be removed from the condenser cooling water by the cooling tower is equal tothe sum of the cooling load plus the heat equivalent of power absorbed by the compressor.An approximate figure of 1.2 kW per kW of refrigeration may be used.The quantity of water to be passed through the tower is dependent on the temperaturedrop allowable between inlet and outlet. A usual figure is 5 K and the inlet water flow willthen be 1:2/(5 4:2) ˆ 0:057 litre/s per kW of refrigeration.The temperature to which the cooling tower may be expected to reduce the condenserwater depends on the maximum wet bulb of the atmosphere and the design of the tower: