Granted Patent EP4281714 : A Feasible Architecture for Direct Warm Liquid Subcooling Defrost in Air-Source Heat Pumps

**NOTICE: This version contains errors in the data/text. Please refer to the latest version for the correct information This work establishes the technical feasibility of the Direct Warm Liquid Subcooling Defrost concept for mitigating defrost-related efficiency penalties in air-source heat pumps. The method recovers otherwise unused thermal energy inherently present in the warm condensed liquid refrigerant by routing this flow directly to a selected evaporator section undergoing defrost, while the remaining parallel-flow sections continue operating in standard evaporation mode. In the streamlined patented embodiment, the proposed architecture significantly reduces the energy penalty associated with defrost cycles. In a more advanced embodiment, the integration of an ejector enables the compressor suction pressure to correspond to the higher evaporating pressure of the non-defrosting sections, thereby effectively eliminating defrost-related inefficiencies that arise from unequal frost accumulation across parallel evaporator sections. In future implementations, the ejector may be replaced by an expander, allowing partial recovery of the expansion work normally dissipated in throttling and offering the potential for further improvements in overall system efficiency.