Energy-efficient control of an air handling unit for a single-zone VAV system

A large fraction of energy consumed by the HVAC (heating ventilation and air-conditioning) system in a commercial building is consumed at the AHUs (air handling units) that condition a mixture of outside and return air to specific temperature and humidity levels. Traditionally, the return air ratio and temperature of the air leaving the cooling coils in the AHU (conditioned air temperature) are maintained at pre-determined set points instead of being based on real-time measurements of occupancy, zone humidity, and outside weather. In this paper, we investigate the potential of energy savings as a function of the complexity of control algorithm. The inputs that can be commanded by the controllers are: air flow rate, return air ratio, conditioned air temperature, and the temperature of air leaving the heating coils in the AHU. Simulation results show that the controllers that use the measurements of occupancy, zone humidity, and outside weather result in significant savings over conventional controllers that do not use such measurements, without sacrificing thermal comfort or indoor air quality (IAQ). Surprisingly, a simple feedback control scheme is found to perform almost as well as a much more complex MPC (model predictive control) controller.