Cascade heat utilisation via integrated organic Rankine cycle and compressor-assisted absorption heat pump system

Abstract

Absorption heat pumps have attracted increasing attention due to the recent interest in high-efficiency waste heat utilisation in buildings. By ways of the outstanding performance of organic Rankine cycle (ORC) for low-temperature heat recovery applications, this paper proposes a new hybrid system integrating an organic Rankine cycle and compressor-assisted absorption heat pump (OCAHP) to improve the operating range and overall performance of the heat pump via cascading heat utilization. A thermodynamic model of the OCAHP system is developed for the evaluation of its performance at different operating parameters. The results show that the system has an excellent performance even at an ambient temperature as low as −20 °C, and its primary energy efficiency is improved significantly compared to both conventional and compressor-assisted absorption heat pumps. The performance improvement is at least 10% over a wide ambient temperature range. Also, it has a greater potential to maintain high-performance operation at a low heat source temperature (below 100 °C) while still meeting the heating requirements. Furthermore, the system shows a good tolerance to the variation of hot water supply temperature. Under a hot water temperature of 60 °C, the primary energy efficiency of the OCAHP is up to 1.5. The above features have proved that the proposed system has a great potential to be used in practical applications and achieve energy efficiency enhancement in typical winter condition.