Cold gas returning from the evaporator to the compressor can be used to pre­cool the warm liquid passing from the condenser to the expansion valve, using a suction-to-liquid heat exchanger (Figure 9.13). In cooling the liquid and reducing its enthalpy, a greater refrigerating effect will be obtained. This gain is offset by the superheating of the suction gas and the resultant reduction of mass flow into the compressor. The overall effect of fitting a suction-to-liquid heat exchanger in terms of thermodynamic efficiency will vary with the refriger­ant and the operating conditions.

The suction-to-liquid heat exchanger will supply the suction superheat nec­essary for safe operation of a direct expansion evaporator, and the coil super­heat may be less, giving more efficient use of the evaporator surface. The phial


Figure 9.13 Suction-to-liquid heat exchanger circuit

Should be located before the heat exchanger, in which case the superheat setting is reduced. It can be located after the heat exchanger, but an external equalizer is then necessary to allow for the gas pressure drop through the exchanger.

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