Biomass-Derived Solvents and Low-GWP Refrigerants as Working Fluids for Sustainable Absorption Refrigeration

A shift toward more sustainable practices is critical for the refrigeration, air conditioning, and heat pump (RACHP) sector, which is responsible for significant greenhouse gas emissions due to its reliance on vapor compression refrigeration cycles. Absorption refrigeration systems (ARS) have been proposed as a promising alternative due to their ecofriendliness, especially when powered by low-grade heat. This work introduces a novel approach by incorporating eco-friendly and biobased solvents as working fluids in ARS for the first time. Five green organic solvents─solketal, propylene carbonate, terpinolene, γ-valerolactone, and Rhodiasolv PolarClean─were carefully selected based on their safety, operational, and environmental profiles, assessed by referring to the CHEM21 solvent selection guide. Subsequently, the affinity and interactions between these solvents and three hydrofluorocarbons (HFCs): R-32, R-125 and R-134a, and two hydrofluoroolefins (HFOs): R-1234yf and R-1234ze(E), were assessed using COSMO-RS quantum chemical calculations. The vapor–liquid equilibrium (VLE) of the binary systems was experimentally determined at several temperatures and pressures, followed by an in-depth thermodynamic evaluation to select the most promising solvent-refrigerant pairs. Finally, the coefficient of performance (COP) and the circulation factor (f) of γ-valerolactone and Rhodiasolv PolarClean-based working pairs were evaluated within the ARS framework, showcasing a significant breakthrough in the development of R-1234ze(E)-based pairs. Notably, the pairs including R-1234ze(E) achieved the highest COP value (0.60) reported to date with HFOs in analogous ARS. Moreover, the compression-assisted ARS (CA-ARS) evaluated proved to be competitive in terms of COP and f when compared to those of conventional pairs. These results highlight the promising potential of green organic solvents and low-GWP HFC/HFO-based working pairs as an effective strategy for reducing emissions and improving the sustainability of the RACHP sector.