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A single screw compressor is widely studied as a promising compressor technology applied in heat pumps. The capacity control mechanism is required for the compressor to satisfy the actual heating capacity under different working conditions. In this paper, the frequency conversion regulating mechanism by changing the motor rotating speed is employed to control the capacity of the single screw compressor. Experimental investigations on a single screw compressor with variable speed for heat pump are carried out under different working conditions to research its performance. The tests have been performed using R22 at evaporating temperatures between -9 °C and 3 °C, and motor rotating speed between 1710 rpm and 2850 rpm. The heating capacity and coefficient of performance(COPh) changed between 47.19 kW and 165.63 kW, and between 1.87 and 3.68, respectively. The volumetric efficiency of the compressor presents a linear decrease by 28.66%–36.04% for different evaporation temperatures when the motor rotating speed decreases from 50 Hz to 30 Hz. Results show that high motor rotating speed has a positive effect on the volumetric efficiency, power consumption, heating capacity, and COPh.
Wen et al. (Tue,) studied this question.