Experimental analysis of a new method for overfeeding multiple evaporators in refrigeration systems

•Overfeeding multiple evaporators connected in parallel in a CO2 refrigeration system.•Optimal use of evaporator heat transfer area.•Evaporator expansion valve control based on cold room temperature.•Liquid collected in the low pressure receiver recirculated by a two-phase ejector.•-13% energy consumption when compared to thermostatic control (at test conditions).

An innovative method for feeding flooded evaporators, arranged in parallel in R744 plants, is presented. In order to promote evaporators overfeeding, an ejector circulates liquid from the low pressure receiver back to the intermediate pressure receiver. Since there is not a need for superheat at the evaporator exit, each evaporator expansion valve can be controlled by a signal representative, either of the evaporator load, or the evaporator performance, such as the air temperature at its inlet or outlet. When compared to dry-expansion evaporator systems, the proposed solution offers energy saving and smooth operating conditions, typical of flooded evaporators, while still maintaining a simple plant lay-out. The concept was experimentally validated: the evaporators were maintained in flooded conditions, while the ejector was able to promote liquid recirculation. Direct comparison with dry-expansion operations was performed. The suggested method is mainly intended for commercial refrigeration plants, where many evaporators are arranged in parallel.