Analysis of hybrid compression absorption refrigeration using low-GWP HFC or HFO/ionic liquid working pairs

Abstract

Absorption refrigeration systems (ARS) are the leading alternative for reducing the electricity costs associated with compression refrigeration systems. However, classical pairs based on NH3/H2O and H2O/LiBr have drawbacks that limit their practical application. In this work, we analyze 16 pairs of refrigerant gases and ionic liquid sorbents based on two low global warming potential (GWP) hydrofluorocarbons (HFCs), R32 and R134a, and two novel hydrofluoroolefins (HFOs), R1234ze(E) and R1234yf, using the low-viscosity ionic liquids [C2mim][BF4], [C2mim][OTf], [C2mim][SCN], and [C2mim][Tf2N]. We provide new data and modeling of the vapor-liquid equilibria of R1234ze(E) with [C2mim][OTf], [C2mim][SCN] and [C2mim][Tf2N]. ARS performance in single-effect (SE-ARS) and compression-assisted absorption refrigeration (CA-ARS), in terms of coefficient of performance (, ), solution circulation factor (), and the thermal and electrical contribution to the total , is evaluated through energy and exergy analyses. The results showed that CA-ARS performs better even at lower generator temperatures. In addition, HFCs returned a better performance than HFOs because of their higher solubility in ILs. The working pair R32/[C2mim][Tf2N] gave the best results, = 0.74 and = 5.4 at 328 K in the desorber, and a maximum of 0.41 at 318 K. Furthermore, the HFO R1234ze(E), with a lower working pressure and negligible GWP, is also a promising option for CA-ARS. In conclusion, we consider that ARS with the HFC or HFO/IL pairs examined in this study shows outstanding potential as a more energy efficient system compared to compression systems, when an inexpensive energy source is available.