Performance of a single-stage recuperative high-temperature air source heat pump

Abstract

• A single-stage recuperative high-temperature air source heat pump is developed. • Exergy efficiency of 27.97% is higher than the existed heat pumps. • Discharge pressure is less than 2 MPa at the hot water temperature 91.68 °C. • n-hexane concentration is 52.36% shifted at optimal condition. Heat energy of 75–100 °C is increasingly used in residential and industrial fields. However, conventional single-stage air source heat pumps suffer low efficiency and poor operating conditions when supplying such high-temperature heat energy. To address the challenging problems, a novel single-stage recuperative high-temperature air source heat pump prototype for tap water direct heating was developed and investigated experimentally. The intrinsic characteristic of the recuperative heat pump makes the prototype simple and components easy to gain. The key impacts of the throttle valve opening, refrigerant concentration, and water flow rate on the system performance were revealed and analyzed with the refrigerant mixture of n-hexane and propylene. Results show the excellent thermodynamic efficiency and working condition of the developed heat pump. When heating water from 23.70 °C to 91.68 °C, the system shows its optimal performance with the coefficient of performance, exergy efficiency, and compression ratio 2.83, 27.97%, and 2.86, respectively. Furthermore, based on the experiment data, systematic thermodynamic analysis on optimal condition indicated that the mass fraction of n-hexane in the cycle is about 52.36% shifted against the initial charging proportion of 36%. Finally, after system performance comparison against the CO 2 transcritical heat pump and auto-cascade heat pump, the recuperative high-temperature heat pump shows excellent efficiency and nice operating condition, which proves the developed heat pump a successful and promising application prospect.