This paper presents a semi-empirical model of scroll compressors and proposes a methodology in order to extend this model to vapor-injection scroll compressors. The model takes into account the ideal evolution of the refrigerant throughout the compressor and considers the main sources of losses in the compression process. The model is able to predict the compressor and volumetric efficiencies in terms of ten empirical parameters, which have a direct physical interpretation. For the model validation, a series of four non-injected scroll compressors of different capacities were tested using R-290 and a scroll compressor with vapor-injection (SCVI) was characterized using R-407C. Results show a correct agreement between the experimental and calculated compressor efficiencies, with a maximum deviation of ±5%. Furthermore, the model estimates accurately the discharge temperature of the refrigerant, compressor power input, and refrigerant mass flow rate in the suction and injection port. Finally, the SCVI model response was evaluated by varying the intermediate pressure and the injection superheat.

ElsevierTello Oquendo, FM.; Navarro-Peris, E.; Gonzálvez Maciá, J.; Corberán Salvador, JM. (2016). Performance of a scroll compressor with vapor-injection and two-stage reciprocating compressor operating under extreme conditions. ABSTRACTThe current paper presents a comparative study between a vapor-injection scroll compressor (SCVI) and a two-stage reciprocating compressor (TSRC) operating under extreme conditions. The present work is divided into two parts: on the first one, both compressors are compared in terms of compressor efficiency, volumetric efficiency, COP, and cooling capacity using R407C refrigerant; on the second part, the seasonal performances of both compressors working in cooling and heating modes are estimated and analyzed. As a result, the SCVI presents better efficiency and COP, compared to TSRC, for pressure ratios below 7.5. This compressor can be used in air conditioning systems and heat pumps, which work under moderate temperature conditions. For higher pressure ratios, the TSRC has better efficiency which subsequently gives higher system COP. This type of compressors can be used in domestic hot water systems operating under severe climates and low temperature freezing systems (under -20°C).

This paper presents a characterization methodology for vapor-injection scroll compressors (SCVI). An SCVI was characterized in a modified calorimetric test bench, which is able to control the intermediate pressure and the injection superheat independently. Based on the characterization results, the injection mass flow rate was correlated with the intermediate pressure through a linear expression, and a modified AHRI polynomial was proposed to estimate the compressor power input. The correlations were used in a simple model to predict the intermediate conditions of the SCVI installed in a heat pump prototype with an economizer. The deviations obtained for the evaporator mass flow rate, injection mass flow rate, intermediate pressure, and compressor power input were lower than 5 % in all cases. The proposed methodology allows evaluating SCVI in a wide range of operating conditions, being only dependent on compressor characteristics and totally independent of the system in which it is installed.

Tello-Oquendo, FM.; Navarro-Peris, E.; Gonzálvez-Maciá, J. (09-2). Comparison of the performance of a vapor-injection scroll compressor and a two-stage scroll compressor working with high pressure ratios.

This paper presents a comprehensive study of two-stage vapor compression cycles with vaporinjection for several refrigerants considering that the heat sink has a limited capacity. The key parameters of the cycle performance are identified and the influence of these parameters on the heating COP is analyzed. The optimum intermediate conditions of the cycle are evaluated using a general model of the cycle, considering two configurations (flash tank and economizer). Based on the optimization results, a correlation is proposed in order to estimate the optimum intermediate pressure, taking into account the temperature lift in the secondary fluid imposed by the application. The correlation uses cycle subcooling as an input, which is a novelty from the current correlations proposed in the literature. In addition, an optimum subcooling control strategy is proposed and finally, the influence of the size of the system components on the COP is studied.