The role of optimum intermediate pressure in the design of two-stage vapor compression systems: A further investigation

The determination of the optimum intermediate pressure (p(m, opt)) is critical for the design of two-stage vapor compression (TSVC) systems, and there exists many studies on it. However, the inter-stage subcooling parameters (epsilon) and the respective efficiencies of the two compressors were not included in the existing estimation formulas for pm, opt. In this paper, six types of TSVC cycles are classified into two categories, and then based on a general expression of COP, the influences of epsilon and the compressor efficiencies on p(m, opt) are analyzed for the cycles using R22 and ammonia as the refrigerants. Results show that, for the ideal cycles, epsilon is a critical influence factor on p(m, opt) in addition to the condensing and evaporating conditions; whereas for the real cycles, both epsilon and the efficiencies affect p(m, opt) significantly. Two revised formulas are established to estimate p(m, opt) for the ideal and real cycles respectively with satisfactory results. (C) 2016 Elsevier Ltd and IIR. All rights reserved.