Experimental study on thermal performance of two-stage ejector heat pump heating system with large temperature drop

Ejector heat pump (EHP) has the advantages of a simple system structure, no moving parts, suitable for low-grade heat sources, and is widely used in the field of central heating and cooling. However, the low ejector entrainment ratio restricts the heating capacity of EHP. To solve this problem, a two-stage ejector heat pump heating system with large temperature drop (T-EHP) was designed and constructed in this paper. The ejector structural profile was optimized using the improved constant rate of momentum change method (I-CRMC) and CFD simulation method. The experimental study compared and evaluated the ejection performance of the I-CRMC ejector and the constant pressure mixing method (CPM) ejector. Furthermore, the thermal performance of T-EHP and EHP under design and variable operating conditions was experimentally studied. The research results indicate that the entrainment ratio of the I-CRMC ejector is relatively increased by 15.09 %∼33.33 % compared to the CPM ejector. The relative errors between the experimental and simulation results of the two types of ejectors are less than 14.67 % and 20.14 %, respectively. Moreover, the high-performance I-CRMC ejector resulted in a relative increase of 12.91 % in the heating capacity of the T-EHP system. Compared to the single-stage system, the heating capacity of the T-EHP system has been relatively improved by 9.41 %. Specifically, the T-EHP heating performance will be significantly improved when the heat source conditions are favorable.