Gray-box models; dynamic modeling of vapor-compression systems; variable-speed heat pumps.
In this paper, a gray-box dynamic modeling approach for variable-speed direct-expansion systems is presented. The overall approach incorporates a multi-stage training procedure that consists of 1) identification of component sub-models from quasi-steady-state performance data, 2) system model integration with estimation of refrigerant charge and 3) fine tuning of thermal capacitances of the evaporator and condenser to capture the system dynamic responses. Compared to traditional physics-based models, the proposed modeling approach has advantages including reduced engineering efforts in the model development phase, improved computational efficiency and reduced uncertainties. The modeling method was applied to a 3-ton variable-speed heat pump and proved to be capable of accurately capturing the system transient behaviors over a wide range of operating conditions.