Numerical Analysis of a Vapor-Injected Reciprocating Compressor for a Multi-evaporator Domestic Refrigerator/Freezer Application

Domestic refrigerators account for ~6% of the energy consumed worldwide and mainly rely on vapor compression cycles to operate. To enable smart and versatile systems, advanced cycle architectures are necessary to optimize their operation and reduce energy consumption. In this paper, a modern three-evaporator domestic refrigerator/freezer using R600a as refrigerant is investigated. To enhance the performance of the cycle, a variable-speed vapor-injected reciprocating compressor has been analyzed and integrated into the cycle architecture. Initial cycle modeling results showed a 12.9% decrease in power consumption. To evaluate additional performance improvements, a detailed mechanistic compressor model of the baseline variable-speed compressor was developed and validated with experimental data. Next, a vapor-injection line was added to the compressor model as an additional flow path to the compression chamber. The injection line has been modeled as a tube connected to an opening on the cylinder wall, which is uncovered during the compression stroke. The injection tube is controlled by a fast-acting solenoid valve to separate injection and suction flow for the compressor. Parametric studies have been carried out to assess the effects of injection timing and injection port diameter on power consumption and overall isentropic efficiency with respect to the baseline compressor. It was found that vapor-injection in the reciprocating compressor can reduce specific work required by up to 10.7%. Based on parametric studies, opening time of the fast-acting solenoid valve directly impacted the compressor efficiency and mass flow rate. An optimal design of the compressor exists by careful selection of the pressure inside the cylinder before injection to reach maximum efficiency.