Thermal gradient optimization in independent cascade heat pumps for efficient ultra-high temperature heating

Air source compression-absorption hybrid heat pumps hold promise for industrial decarbonization, but their current temperature lift capacity remains insufficient to meet ultra-high temperature requirements. Moreover, in elementary independent cascade configurations, all compression sub-loops operate at the same evaporation temperature. This lack of targeted optimization results in higher compressor power consumption and reduced efficiency. To overcome these limitations, an advanced independent cascade design and two derivative heat pump configurations are constructed in this paper. These innovations aim to broaden the suitability of air source heat pumps for ultra-high temperature applications and push the boundaries of efficiency. Based on validated models, the results indicate that the proposed independent cascade evaporative thermal coupling heat pump can achieve a heated temperature of 204 °C from an input source of 10 °C, extending the temperature lift capacity by around 18 °C compared to the elementary independent cascade baseline. This advanced configuration, featuring optimized thermal gradient coupling between sub-loops, significantly reduces irreversible losses by 70.7 % relative to the baseline system. Moreover, it demonstrates marked improvements in performance, with COP and ECOP increasing by 57.9 % and 60.3 %, respectively, while reducing initial investment costs by 6.6 % to 8.3 %. These findings enhance the feasibility of sustainable industrial heating.