Investigation on transient response of the direct expansion solar assisted ejector-compression heat pump cycle for water heater

Aiming to provide data support for the control-oriented design and practical application, the transient response characteristics of the direct expansion solar assisted ejector-compression heat pump cycle for water heater is investigated in this study. The dynamic simulation model of the presented system is built, and relevant experimental items are also conducted to verify the simulation model. The experimental and simulation results during a typical water heating process show satisfactory agreement, and the maximum forecast error of four main operation parameters is less than 6.6%. The system transient responses under the step change of the expansion valve opening degree are explored by both simulation and experimental methods, and the simulation model still appears high forecast precision. Thereinto, the maximum simulation error of the refrigerant flow rates is less than 5.2%. The system dynamic responses under the sudden changes of the ejector nozzle throat area and solar radiation intensity are further evaluated based on the verified model, and the coupling relation of the system pressure and refrigerant flow rate is further revealed. In addition, further simulation research proves that substituting R134a with R1234yf and R1234ze(E) in the present system has little impact on the system dynamic characteristics.