Refrigeration plant - has pressure sensor for evaporation pressure and control circuitry for induction motor-driven compressor to keep this pressure constant

摘要

A refrigeration plant has an evaporator followed by a compressor and then a condenser whose outlet feeds the evaporator. A pressure sensor (16) establishes the actual evaporation pressure and is linked through control circuitry to the compressor (14) to keep the evaporation pressure constant. If the setpoint for evaporation pressure is exceeded, the speed of the compressor is reduced, and the speed is increased if the evaporation pressure falls below the setpoint. The compressor is induction motor-driven and the speed control is done by frequency changing, ie, frequency reduction for speed reduction. The control circuitry incorporates a comparator for the actual and setpoint pressure values.