A robust fault detection and diagnosis strategy for multiple faults of VAV air handling units

•Robust FDD strategy for multiple faults of VAV air handling units is proposed.•Fault detection method of AHU systems by using residual-based EWMA control chart.•Rule-based FDD method is extended to isolate multiple faults of air handling unit.•Robust FDD strategy proposed is validated on real VAV air-conditioning systems.

Fault detection and diagnosis (FDD) is critical to reliable operation and energy efficiency of variable-air-volume (VAV) air-conditioning system. In this paper, a robust fault detection and diagnosis strategy is presented for multiple faults of air handling units by using the residual-based exponentially weighted moving average (EWMA) control chart method and the rule-based fault diagnosis method. Residual-based EWMA control chart with designing chart limits is used to detect faults of air handling units. In order to provide a level of robustness with respect to modeling errors, control limits are determined by incorporating uncertainty information into EWMA control chart. Furthermore, the rule-based fault diagnosis method is extended to isolate simultaneous multiple faults of VAV air handling units in the mechanical cooling operation mode. Twenty-six expert rules consisting of system behavior rules and energy related rules are used to diagnose twenty-two faults of air handling units. The fault detection and diagnosis strategy was validated by using the operating data from real VAV air-conditioning systems involving multiple artificial faults. The results of validation show that residual-based EWMA control chart with designing control limits is a robust tool of fault detection for air handling units. The rule-based fault diagnosis method presented is efficient to isolate multiple faults of air handling units.