Thermodynamic analysis and performance evaluation of a solar-assisted high temperature heat pump system with lubricants

The conventional high-temperature steam (≥100 °C) used for heating typically comes from coal-fired, gas-fired, or electric boilers, but it has lower heating efficiency. The solar-assisted air source compression heat pump system can play a pivotal key role in generating high-temperature steam and reducing carbon emissions. Based on the concept of the energy cascade utilization and production, a novel solar-assisted heat pump system with an integrated double-source two-stage compression heat pump cycle (SAHP-DTC) for high temperature steam production is proposed, and R1336mzz(Z) is used as refrigerant. In the novel system, quasi-two-stage vapor injection compression coupled with a multi-cooled heat exchanger is applied to form an air-source quasi-two-stage compression heat pump cycle, solar-assisted dual-source quasi-two-stage compression heat pump cycle, and solar-assisted cascade heating compression heat pump cycle, so as to boost the contribution of low-grade energy to heating performance. Besides, the compatibility between refrigerant and lubricants is experimentally investigated, and the pressure-enthalpy diagrams of the refrigerant/lubricant mixture are plotted. The results indicate that the proposed system 24/7 operation for 110 ℃ steam production can respectively enhance the average heating COP by 5.41% and 3.85% in a typical winter day in Beijing and Shenyang City, compared with the conventional air-source quasi-two-stage compression heat pump system. Polyolester oil is recommended to be applied in the R1336mzz(Z) high-temperature heat pump system to improve system thermal performance. The presented system achieves a payback period of 8 years under the given operations, and the novel system can remarkably reduce the greenhouse gas carbon emissions.