Experimental comparison of cycle modifications and control strategies for a multi-stage two-evaporator transcritical CO 2 refrigeration cycle.

Abstract

A viable solution to decrease the environmental impact of the HVAC&R industry is the use of natural refrigerants such as Carbon Dioxide (CO2). CO2 has a global warming potential (GWP) of 1, is non-flammable, and is low cost. However, its high critical pressure and low critical temperature require advanced cycle modifications to improve the system coefficient of performance (COP) to be comparable or higher than systems utilizing conventional refrigerants. This paper presents preliminary validation of a transcritical CO2 cycle test stand that can compare six cycle architectures, as well as results from a comparison of ejector and electronic expansion valve (EXV) mode. The aim is to provide a meaningful comparison of these modifications, consisting of two stages of open economization and both EXV and ejector expansion. Preliminary experimental tests were conducted in order to quantify trade-offs between performance improvements and architecture costs. Design recommendations are provided along with future work.