Heat pumps using zeotropic mixtures for heating and cooling applications: A literature review

Advances in heat pump technologies have been dramatic over the past decade and innovations in this area have been countless. While the concept of zeotropic mixtures is not new, recent developments in their composition, novel applications and system designs, and modern analysis techniques have opened new research areas, challenges, and opportunities. For heat pumps specifically, using zeotropic mixtures as the working fluid to get a non-isothermal phase-change through the evaporator and condenser results in a higher coefficient of performance (COP) than any other heat pump technology operating within the same temperature lift range and capacity. Studies show that COP enhancement can be even up to 30%; although such heat pumps are associated with technical challenges including complexities in the design of the components (like heat exchanger and compressor), the mixture component fractionation, uneven heat transfer throughout the condenser and evaporator, etc. This study presents a thorough review of studies on zeotropic heat pumps to dig into their recent advances, applications, pros and cons over conventional heat pumps for certain applications, technical challenges yet to overcome, and suitable mixtures for different operating temperature ranges. The article will also provide readers with a concrete understanding of the operation principles of such heat pumps and future possible works in this context to contribute to the state-of-the-art.