采用复叠式空气源热泵系统可以提高空气源热泵这一节能技术在冬季寒冷地区的适应性。与常规空气源热泵一样，复叠式空气源热泵在供热运行中也会遇到结霜和除霜问题，根据本课题组之前的研究发现复叠式空气源热泵无法照搬常规空气源热泵的除霜方法，而缺乏有效的除霜方法直接影响复叠式空气源热泵的制热效果与系统的可靠性。本项目创新性地提出相变蓄能复叠式空气源热泵除霜新系统，通过高低温级循环在不同运行模式时的能量存储和转移，实现为低温级换向除霜和对高温级持续供热的目的。本项目将以理论和实验相结合的研究手段，研究该新系统的可行性与可靠性；并展开对除霜过程中相变材料多温位相变过程及高低温级循环共用低位热源而产生的耦合关系等关键问题进行研究，建立相变蓄能器多温位释热模型，并在此基础上建立除霜过程中的高低温级耦合模型，为进一步对优化除霜过程，系统优化设计等方向进行更为深入的研究提供理论基础。

In order to encourage the application of air source heat pumps (ASHPs) in cold area due to energy conservation and sustainable development, adopting cascade air source heat pump (ASHP) is a promising option. As traditional ASHPs, when cascade ASHPs are operated in heating mode, frost/defrost phenomenon may become a problem However，according to previous research, cascade ASHP cannot simply copy the defrost method of traditional ASHP. Lack of effective defrost method for cascade ASHPs will directly affect the energy efficiency and reliability of the cascade ASHP system. Therefore, this project proposed a novel thermal energy storage (TES) based reverse cycle defrosting method for cascade ASHPs. During heating mode, the phase change material heat exchanger (PCM-HE) in the low stage cycle stores surplus heat, which is used as the low temperature level heat source to melt the frost on the outdoor coil for low stage cycle, and to supply heat continuously for high stage cycle. This project will firstly investigate the feasibility and reliability when using the novel TES based reverse cycle defrosting method for cascade ASHPs. Then, theoretical and experimental research on the multi-temperature level phase change process occurring during defrosting mode, and the coupling mechanism of the high stage cycle and low stage cycle during defrosting mode resulting from sharing the same low temperature level heat source are also carried out. Multi-temperature level phase change model and coupling model of high stage cycle and low stage cycle during defrosting process will be developed. The successful carrying out of the proposed project will be useful on further research on optimization of defrost control method and system design.