Performances of a refrigeration compressed air dryer using a natural refrigerant (R744).

A compressed air dryer is a common application for a vapor compression circuit. Typical working conditions for this circuit are evaporating temperature between 0°C and 5°C and condensing temperature variable between 35°C and 65°C. Generally, a HFC refrigerant fluid is used in this kind of application, in particular R134a , R407C and R404a. In any case all these refrigerant HFC fluids have a high GWP value. As consequence it is interesting to look for alternative refrigerant fluids with lower GWP value but with equal or comparable energy efficiency. Compressed air dryer with cooling capacity above 50kW are usually designed using flooded evaporator with special control to guarantee stable air dew point temperature. Important parameters to take into consideration for this application are dew point temperature of compressed air after the treatment and energy consumption. In this study performances of a compressed air dryer unit using R744, in transcritical condition as refrigerant fluids, are presented. A special dryer unit has been designed using R744, built and tested. The results demonstrate how, from an air side point of you, performances are changing. The considered parameters are the energy consumption of the compressor and the dew point temperature reached by the air. Finally, a short overview on the economic impact of the new design is presented and possible future improvement on the efficiency in particular related to the control.