EXPERIMENTAL INVESTIGATION OF NH{sub}3/CO{sub}2 CASCADE SYSTEM AND COMPARISON TO R404A SYSTEM FOR SUPERMARKET REFRIGERATION

摘要

This study investigates the performance of an NH{sub}3/CO{sub}2 cascade system for supermarket refrigeration application in a laboratory environment. The tested CO{sub}2 system is designed and scaled to fulfill the requirements of an average size supermarket in Sweden. Possibility for hot gas defrost in the freezers has been investigated and compared to the conventional electric heaters defrost method. Two cascade condenser arrangements have been evaluated. The cascade system has been compared to R404A system installed in the same laboratory. The results show that connecting the cascade condenser via thermosyphon or hot gas de-superheat arrangements yields good system stability and heat transfer performance. Hot gas defrost successfully defrosted the freezer evaporator but with long period and higher energy consumption compared to the conventional electric defrost method. The tested cascade system had up to 60% higher total COP compared to the R404A system installed in laboratory.