Fault-tolerant supervisory control of VAV air-conditioning systems

The paper describes a supervisory control scheme that adapts to the presence of degradation faults and minimises any resulting increase in energy consumption or deterioration in occupant comfort. Since there is a high degree of uncertainty associated with the results of any fault identification scheme in information-poor systems of this type, the supervisory control scheme uses fuzzy models to predict the control performance and a computationally undemanding optimisation scheme to determine the most appropriate set-points. The fault-tolerant control scheme is developed and evaluated using a detailed computer simulation of a multi-zone, variable-air-volume (VAV), air-conditioning system. The fuzzy models relate the performance of the terminal-boxes, the air-handling unit and the chiller to fuzzy descriptions of the cooling load, the supply air and chilled water temperature set-points, and the amount of air-side and water-side fouling. Results are presented that demonstrate the ability of the fuzzy models to predict the performance and show how the power consumption of the air-conditioning system varies with set-point changes and the presence of both water-side and air-side fouling. The main factors that determine the suitability of a particular air-conditioning system for fault-tolerant control are also discussed. (C) 2001 Elsevier Science B.V. All rights reserved.