CO2 Refrigeration withIntegrated Ejectors : Modelling and Field Data Analysis ofTwo Ice Rinks and Two Supermarket Systems

Abstract: With the increasing importance of CO2 as natural refrigerant with low Global Warming Potential(GWP) ejectors have been used in a number of recent installations to recover expansion work atthe high operating pressures of these systems. In colder climates, this is particularly seen in combinationwith heat recovery due to the high compressor discharge pressures.This work analyses the field measurement data of two ice rink refrigeration systems with integratedvapor ejectors and two supermarket refrigeration systems with integrated liquid ejectors, alllocated in northern Europe. The aim is to evaluate the interaction of the ejector with the refrigerationsystem in practical applications. A theoretical model of the ejector systems is developed andevaluated in parallel as a reference for the analysed system installations.The model of the analysed vapor ejector system shows an increasing eciency improvement potentialby the ejector for higher gas cooler outlet temperatures, while the liquid ejector systemmodel indicates higher eciency improvement potential at relatively lower gas cooler outlet temperaturesand pressures.From the vapor ejector field data evaluation, this is confirmed with additional findings of lowejector work recovery eciencies at low gas cooler outlet temperatures. Furthermore, problemsin the ejector operation are found for too low evaporation temperatures in one of the systems. Inaddition, an unstable ejector control at certain operating conditions is linked to a decreasing ejectorperformance. While the ejector is found not to provide any significant savings in one of the systemsmainly due to low evaporation temperatures, the other ice rink system is found to achievetotal energy savings of 7% from the ejector.For the liquid ejector field data evaluation, the ejectors are found to work as expected for the purposeof removing liquid from the low-pressure receiver. However, overfed evaporation conditionsare only found temporarily for most cabinets in the analysed systems, with remaining high averagesuperheat values. Low required air supply temperatures in the cabinets and the dimensioning of theexpansion valves at the evaporator inlet are identified as possible limitations for a further decreaseof the superheat and increase of the evaporation temperature.