Energy-efficient control of under-actuated HVAC zones in buildings

We study control-oriented methods of improving energy efficiency of “under-actuated” heating, ventilation, and air-conditioning systems in commercial buildings where multiple rooms are served by a single variable air volume box. Two novel control algorithms are studied: one is a rule-based, feedback controller that uses real-time occupancy measurements, and the other is based on model predictive control (MPC) that uses predictions of occupancy and other exogenous inputs. In an under-actuated zone, flow rate and temperature of ventilation air to individual rooms in a zone cannot be independently controlled. These have not been studied in the literature but are quite common in commercial buildings. Our study finds that there is potential for significant energy savings relative to conventional controllers for under-actuated zones-even when occupancy in the rooms is vastly different-when independent heating is available for each room. Energy efficiency of simple, rule-based controllers that use occupancy measurements was found to be highly dependent on choice of temperature constraints during unoccupied times. Depending on this choice, MPC may or may not perform better than rule-based control.