Analysis of Absorption-Compression Hybrid Refrigeration Systems for Using Low-Temperature Heat Sources

Abstract

The main objective of this study is to explore and compare the energy and exergy performance of main configurations of nonhybrid (conventional), hybrid (with low- and high-pressure-side booster compressor), and absorption refrigeration systems using LiBr–H2O and H2O–NH3 working solutions, with focus on their ability to efficiently utilize low-temperature driving heat under hot climate conditions and to address their limitations. At a condensing temperature of 40 °C, the nonhybrid absorption systems can operate at generator temperatures as low as 81 °C and 102 °C for LiBr–H2O and H2O–NH3 systems, respectively, with a coefficient of performance (COP) of 0.67 and 0.30, respectively. Hybridization of the absorption refrigeration units permits the operation of the LiBr–H2O generator at as low as 70 °C, and of the H2O–NH3 generator at as low as 89 °C, with COP 38% higher than that of the nonhybrid system. The high-pressure-side hybridization reduces the COP, but the low-pressure-side hybridization has a COP comparable to that of the nonhybrid system operating at higher generator temperatures. Hybridization of the system on both sides complicates it and is thus justified when heat is available only at the lower generator temperature (70 °C). Hybridization when the generator temperature exceeds 85 °C for the LiBr–H2O system, and 120 °C for the H2O–NH3 system, has no operating advantage because the simpler nonhybrid system can operate with a higher COP (0.84 versus 0.8).