Extremum-Seeking ESC VRF MBD
To a VRF (Variable Refrigerant Flow) system, outdoor unit (ODU) energy consumption is the combination of the power consumption of compressors and outdoor fans. The combined power consumption changes with discharge pressures and other conditions. Discharge pressures are controlled to its’ setpoint by manipulating fan speed. There are optimal discharge pressure points, where the combined power consumptions are at its’ minimum. Most common control approaches in industry on the discharge pressure is setting them to a constant value or calculating as a function of compressor speed and ambient temperature. Fixing it to a constant value is not a desired solution since the optimal pressure points change with load, ambient temperature and other operating conditions. Calculating as a function of compressor speed and ambient temperature, though two major factors are in the consideration, still needs lab tests and calibration to find the relation between the energy consumption and discharge pressure. Since VRF system consists multiple ODUs and IDUs (Indoor Units), the task of lab tests could be overwhelming. In this work, ESC (Extremum-Seeking Control) is used to automatically find the optimum discharge/suction pressure points when VRF is in cooling/heating operation. ESC algorithm is implemented into the VRF equipment control. When ESC is enabled, a small excitement signal applies to discharge setpoint, power consumption of compressors and fans is monitored. ESC will find the optimal discharge setpoints to minimize the combined power consumption. ESC is active in all normal operation conditions, it will optimize the energy consumption over all load ranges of heating/cooling and heat recovery operation. Simulation has been conducted to demonstrate the potential savings on the outdoor unit energy consumption.