Dynamic simulation of air-to-water dual-mode heat pump with screw compressor

A dynamic model of air-to-water dual-mode heat pump with screw compressor is presented here. The high-pressure and low-pressure segments are divided into three control volumes, including the refrigerant inside tube, the tube wall and the fluid outside tube that is water or air. Time dependent ordinary differential equations are obtained from the mass and energy balances for each control volume. As the compressor, thermostatic expansion valve (TEV) body, and reversing valve have very small thermal inertias, steady-state models are applied for the compression, throttling, and leakage processes. The relationship between the temperature of the saturated liquid–vapor mixture in TEV’s bulb and the temperature of the refrigerant vapor at the evaporator exit is described with a time dependent ordinary differential equation. System simulation is finally carried out with ‘predictor–corrector’ and ‘adaptive integration step’ methods. Simulated results are in good agreement with the measured data, which lead to conclusion that the model can be used as a tool for the product development.