Experimental validation of the theoretical ejector model in a low-grade waste heat refrigeration system using R1233zdE as a working fluid

Rising electricity prices and environmental regulations make it increasingly economically justifiable to utilize low-temperature waste heat, generated as a by-product of many technological processes. One potential application is the conversion of heat into cooling capacity using an ejector refrigeration system, to replace conventional electric-consuming cooling systems. Such systems, despite numerous descriptions in the literature, have not found industrial applications up to date. This work presents experimental results on the first commercial prototype cooling system driven by 200 kW waste heat of ultra-low temperature between 60 degrees C and 70 degrees C coming from the oil system of air compressors operating under real industrial operating conditions. A refrigeration system configuration based on the use of heat recovery downstream of the ejector and splitting the waste heat recovery heat exchanger into two stages was applied. The low GWP and low-pressure HFO R1233zd(E) refrigerant was used as a working fluid. The high-temperature cooling parameters, equivalent to the glycol temperature of 16 degrees C/19 degrees C (outlet/inlet of the evaporator), were examined and the COP of 0,25 was obtained. To obtain such a promising COP value, the critical and subcritical parameters of the ejector were investigated. Based on the experimental results the validation of the ejector theoretical model was performed for low-pressure refrigerant. The ejector component characteristic efficiencies were optimized for the ejector calculation model, and ejector key performance parameters were estimated to a high accuracy. The average relative error in the estimation was 7.1%, 4.5%, and 13.7% for the mass entrainment ratio, pressure ratio and ejector total efficiency, respectively. The resulting accuracy is sufficient from the perspective of refrigeration system design.