Vapour quality determination for heat pumps using two-phase suction

Abstract

For residential heat pumps, R32 becomes one of the most widely used refrigerant, thanks to an environmental impact much lower than R410A. However, with a classic suction superheat control, R32 induces higher discharge temperatures. Two-phase suction is thus generally allowed in rotary compressors to lower the discharge temperature. In theory, this process can also improve the heat pump performances. However, using two-phase suction for real-time performance optimization implies to identify and control the suction vapour quality. In this study, an iterative method using the compressor energy balance and the compressor efficiencies is presented to determine the suction vapour quality and refrigerant mass flow rate without using a flowmeter. An R32 air-to-air heat pump is then experimentally tested. The reference values are indirectly measured through the mass flow rate measurement and the compressor energy balance. A correlation is thus presented, giving the vapour quality from the operating parameters. If the volumetric or global compressor efficiencies are known, the proposed iterative method allows to calculate the vapour quality with a 0.4 % accuracy. Moreover, this method gives the refrigerant mass flow rate and heating capacity with a 1 % accuracy. The sensitivity of the method is evaluated considering a 10 % error on the volumetric or global efficiency values. In this case, the suction vapour quality values are kept within 2.5 % of the reference measurement. In addition of allowing a precise control of two-phase suction, this method can also make the in-situ performance measurement of these heat pumps possible.