An advanced cascade method for optimal industrial heating performance in hybrid heat pump

Air is a readily available and renewable source, but its efficient utilization for industrial heating is hindered by the significant temperature mismatch between the low-grade air source and the high-temperature industrial demand. Heat pumps can elevate the source temperature from low to high levels. However, there is still a significant knowledge gap in achieving output temperature exceeding 90 °C when the input source is below 30 °C. While there are some preliminary studies on air-source heat pumps operating in the mentioned temperature range, they have yet to distinguish the respective coupling temperatures required for different cascaded components. Therefore, the optimal cascade configuration between various sub-cycles has not been established, and the full efficiency potential remains untapped. To address the identified limitations, in this work, an advanced cascade method is proposed and applied to the compression-absorption heat pump (CAHP). The novel cascade method allows independent control of the coupling temperature in different branches as needed, facilitating an optimal cascade configuration between various subloops. Consequently, the operating efficiency of CAHP is optimized. Simulation results show that the proposed cascade method reduces the exergy destruction of CAHP by 6.3% compared to the existing mode. Moreover, it always achieves higher efficiencies in the studied conditions, with a maximum increase in the coefficient of performance and exergy coefficient of performance by 16.2% and 19.2%, respectively. Under ambient temperature of 10 °C to –30 °C and an output temperature of 100 °C, the improved cascade CAHP exhibits an increase in heating capacity, ranging from 57.2% to 238.4% higher than the existing mode. These advantageous features contribute to achieving cleaner industrial heating with air source heat pumps. © 2024