Recent advances, challenges and future prospects on frost-free air source heat pump technology with integrated solid desiccant dehumidification

In this paper, the research progress of frost-free air source heat pump (FFASHP) technology with integrated solid desiccant dehumidification is systematically reviewed in terms of technical principle, desiccant materials, desiccant-coated heat exchangers (DCHEs) and FFASHP system characteristics. The energy, economic and environmental benefits of the existing FFASHP systems are evaluated and compared with traditional reverse-cycle defrosting air source heat pump (ASHP) systems. These systems have numerous unresolved issues and challenges that impede their large-scale application. The future research direction is proposed in five aspects: new materials and novel structures, system optimization, performance evaluation, advanced models and standards, as well as control strategy optimization. FFASHP technology needs to introduce external heat sources (such as solar radiation heat, system waste energy and industrial waste heat) as the main energy of the desiccant regenerator and heat storage device (HSD) in accordance with regional climate characteristics. In addition, a new generation of FFASHP technology integrating heat storage and dehumidification should be developed for different climate regions, and a reasonable and scientific system performance evaluation method should be planned. This review is expected to provide some ideas for the innovation and industrialization of FFASHP technology.