Revision Exercises 5. An R 22 refrigerating plant with back pressure control has a capacity of 30,000 kJ/h at -30°C and 45,000 kJ/h at -25°C. The refrigerant flow is con- trolled by thermostatic expansion valves with 8°C superheat. The condensing temperature is 35°C. There is no heat exchanger. The vapours are superheated by 15°C in the suction line. The compressor is single-acting and has four cylinders. It runs at 930 rpm and its bore/stroke ratio is 1.25. Volumetric efficiency may be assumed as 70 per cent. Calculate the dimensions of the cylinders. Also calculate the power consumption and COP.