Real-time minimization of power consumption for air-source transcritical CO₂ heat pump water heater system

Based on Extremum Seeking Control, a real-time optimization strategy is proposed for minimizing the power consumption of a transcritical CO₂ heat pump system. An analytical framework is established to justify the equivalence between power minimization and the maximization of coefficient of performance. As compared to the COP feedback, power feedback based control avoids the need for several sensors beyond the simple and reliable power measurement. The proposed ESC scheme is based on three measurements of power consumption, high-pressure and gas cooler outlet water temperature. Simulations are conducted for several scenarios: a fixed operation condition, change of ambient condition and realistic ambient temperature condition. For all simulation cases, the water inlet temperature is fixed at 12 °C, while the water outlet temperature is set as 60 °C. Simulation results show that ESC is able to search and even track both fixed and slowly varying optimum discharge pressure without need for system model.