The heat to be removed in the condenser is shown in the p-h diagram (Figure 6.1) and, apart from comparatively small heat losses and gains through the cir­cuit, will be

Heat taken in by evaporator + heat of compression

This latter, again ignoring small heat gains and losses, will be the power input to the compressor, giving

Evaporator load + compressor input power = condenser load

Condenser load is stated as the rate of heat rejection. Some manufacturers give ratings in terms of the evaporator load, together with a ‘de-rating’ factor, which depends on the evaporating and condensing temperatures.

Evaporator load X factor = condenser load

The provision of a separate oil cooler will reduce condenser load by the amount of heat lost to the oil and removed in the oil cooler. This is of special note with oil-injected screw compressors, where a high proportion of the com — 74 pressor energy is taken away in the oil. This proportion varies with the exact


-40 -2D 0 20 40 60 BO 100 120

1UJ 130 atu 2iD JUJ 330 4UU 450 3UG

Enthalpy [kJ/kg]

Figure 6.1 Condenser load p-h diagram

Method of oil cooling, and figures should be obtained from the compressor manufacturer for a particular application.

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