Combined exergy-pinch point analysis of a multi-valve flexible heat pump with integrated latent thermal energy storage for defrosting operation

This study presents a combined exergy and pinch point analysis of a multi-valve flexible heat pump system integrated with latent thermal energy storage, with a focus on its defrosting operation. Exergy destruction is evaluated at both component and system levels in heating/charging and defrosting/discharging modes under various operating conditions to identify key inefficiencies and mitigation strategies. Results show that exergy efficiency in defrosting mode is nearly double that in charging, primarily due to the lower compression ratio and inactive evaporator. Compressor isentropic efficiency is found to be the dominant factor influencing system losses, with exergy destruction increasing by 43 % and 35 % in charging and defrosting, respectively, when its efficiency drops from 100 % to 75 %. Although the storage–refrigerant temperature difference has less influence than the compressor, it significantly affects both the storage and overall system exergy destruction, especially during defrosting. When this temperature difference increases from 0 to 5 K, total system exergy losses during defrosting rise by 30 %. Pinch point analysis highlights the critical role of heat exchanger design, as variations in external water loop temperatures can result in up to a 70 % increase in system exergy efficiency. These findings offer practical guidance for optimizing the design and operation of the flexible heat pump under non-ideal conditions.