A Theoretical and Experimental Analysis of a Self-contained R-290 Refrigeration Unit Applied to a Glass Door Reach-in Supermarket Display Case

This paper presents a theoretical and experimental analysis of a self-contained variable speed R290 refrigeration unit applied to a typical 1.25m long two-glass-door reach-in supermarket display case, originally designed to run on an integrated R404a single speed refrigeration unit. A semi-empirical mathematical model was put forward to predict system energy consumption and cabinet psychometrics as a function of environmental conditions (ambient temperature and relative humidity), compressor model (single-speed, variable-speed and compressor displacement), refrigerant fluid (R290 and R404a) and geometry (heat exchangers overall heat transfer coefficient). One energy consumption test was performed at 32°C ambient temperature and used to calibrate components overall heat transfer coefficients. The model validation was then performed by using the calibrated model to predict the system energy consumption at 27°C ambient temperature. A good agreement between experimental and numerical results was found with errors lower than 1% and 3% on energy consumption and compressor running time ratio respectively. Finally, the model was applied to predict annual energy consumption for two units (R290 self-contained and R404a integrated) as a function of the monthly average ambient temperatures for Joinville, Santa Catarina, Brazil. The simulation results indicate an annual energy consumption saving up to 30% when a self-contained R290 variable speed hermetic refrigeration unit is applied to a cabinet originally designed for an integrated R404a single speed compressor refrigeration unit