Variable speed hermetic reciprocating compressors for domestic refrigerators

This paper contains both a theoretical and experimental investigation of some of the fundamental characteristics of a small variable speed hermetic reciprocating compressor intended for application in domestic refrigeration. The results of a previously published simulation model for variable speed compressors are compared with experimental results obtained in a compressor test bench. The influence of speed on compressor performance is discussed with focus on valve modelling and internal thermal phenomena. Further plans for development and validation of the model as well as experimental investigations are discussed. NOMENCLATURE Cc Contraction coefficient [ -] ToAs,Avo Avg. temperature of gas in shell [OC] COP Coefficient Of Performance [ -] TMOTOR Motor temperature (stator) [OC] d Diameter of valve port [m] ToiL Temperature of oil in shell [oC] HRR Heat Rejection Ratio [-] Tsc Temperature of gas in suet. chamber [OC] N Compressor speed [rpm] TsHELL Avg. temperature of shell surface [OC) Nw.x Max compressor speed [rpm] Xw.x Max valve lift [m] rh Mass flow of refrigerant [kg/s] X MEAN Mean valve lift [m] MR Mixing ratio [-] dp Pressure difference [k.PaJ pl\IIOTOR Power consumption of motor [W] T(IS Isentropic efficiency [-) QCONV Heat rejected from shell by convection[W] TJM Motor efficiency [ -] QE Refrigeration capacity [W] TJVOL Volumetric efficiency [ -] QRA.D Heat rejected from shell by radiation [W] s Loss coefficient for valves [ -] Tc,INI.Er Temperature of gas in suction stub [OC] p Density of gas TosCH Discharge gas temperature [OC] [kg/m 3 ] INTRODUCTION Theoretical and practical investigations [1], [2] have shown that continuously controlled domestic refrigerators using variable speed compressors have a significantly lower energy consumption compared to the conventional refrigerators operating in on/off-mode. The major reason for the reduction in energy consumption is the significant improvement in the operating conditions of the refrigeration system (higher evaporation temperature and lower condensing temperature). In connection with the investigations mentioned other theoretical investigations [3] have shown that the performance of the compressor may also depend on the speed. To be able to design a continuously controlled refrigeration system for variable speed compressors it is therefore necessary to know how the speed of the compressor will influence it's performance in the refrigeration system.