空气源热泵具有高效节能、安全清洁的独特优势，是我国北方地区冬季燃煤采暖的主要替代方式，已被推广应用。然而，传统空气源热泵普遍存在能效、制热能力、环保性和安全性不能兼顾的突出问题。随着蒙特利尔议定书基加利修正案的签订实施，传统空气源热泵将因缺乏高效的安全环保工质，在我国北方地区的采暖应用中受到严重限制，并将制约我国空气源热泵产业的快速发展。本项目以提高热泵的能效和制热能力为目标，兼顾环保性和安全性，构建一种大温跨空气源复合热泵及适用其中的大沸程安全环保混合工质。从理论和实验两方面开展系统研究：揭示该混合工质的相平衡特性及其可燃性规律，探索该复合热泵的循环机理，研究其运行特性，寻求优化系统性能的有效途径，最终实现高效、高制热能力、环保和安全可靠的空气源热泵采暖。本项目的研究成果可望丰富混合工质热泵的科学理论，为空气源热泵在我国北方地区中大型供暖系统中的长期应用提供一个有效的解决方案。

Because of its unique advantages of high efficiency, energy saving, cleanness and safety, air source heat pump (ASHP) has been widely applied as a main alternative to coal-fired winter heating in northern China. However, traditional air source heat pumps generally were hard to keep the balance between energy efficiency, heating capacity, environmental protection and safety. With the implementation of the Montreal Protocol Kigali Amendment, traditional air source heat pumps will be severely restricted in heating applications in northern China due to the lack of efficient, safe and environmentally friendly working substances, which will restrict the rapid development of air source heat pump industry in China. Aiming at improving the performance and heat capacity of heat pump, the project proposed a kind of compound ASHP under the large-temperature-span working condition. Taking into the consideration of safety and environmental protection, mixing working substances with large temperature glide will be selected and applied in this ASHP. Theoretical and experimental studies will be carried out to: (1) reveal the phase equilibrium and flammability characteristics of the mixed working substances; (2) explore the working mechanism and the operating characteristics of the compound ASHP; (3) seek an effective way to optimize system performance and ultimately achieve reliable ASHP heating with high efficiency, high heat capacity, safety and environmental protection. The research findings of this project are expected to enrich the scientific theory of the heat pump using the mixed refrigerants and provide an effective solution for the long-term applications of ASHP in medium- and large-scale heating systems in northern China.