Advanced HVAC Control: Theory vs. Reality

Abstract Intelligent control of HVAC equipment is a key step towards improving the energy efficiency of commercial buildings. Although advanced control techniques have been developed and validated under real conditions, numerous buildings are still being poorly controlled due to wrong setpoints, incorrect PID settings, no coordination of individual PID loops, and other practical problems. This paper aims to summarize the major contributors to inefficient HVAC control and outline possible approaches towards better control strategies. Three areas are discussed: performance monitoring tools, rule-based control strategies and model-based predictive control (MPC). Performance monitoring tools help control engineers to quantify the performance of a particular control strategy, compare multiple control strategies among themselves, and define a baseline for such comparisons. Rule-based control strategies utilize various setpoint resets, rules and other heuristics to reduce HVAC energy consumption; however, such methods yield sub-optimal solutions only. Finally, MPC is a powerful and industrially-proven technology for optimal control of complex systems, but its use in building control seems to be so far limited. The paper analyzes challenges and constraints when implementing a control strategy in real projects, and covers topics such as missing sensors, legacy controllers and legislative changes needed to motivate building owners towards more efficient facility management.