Fault impact analysis and prioritization for chilled water plants with chiller and water-side economizer

Fault impact analysis is critical for quantifying operational risks, advancing fault detection and diagnosis, and guiding robust control strategies. Dual-source chilled water plants (chillers + water-side economizers, WSEs) are increasingly adopted for energy efficiency, but their hybrid configuration introduces additional fault pathways that compromise reliability and performance. Existing studies on single-source systems cannot fully capture dual-source vulnerabilities as they have different configurations and operation modes. To fill this gap, this study presents a comprehensive fault impact analysis of a chiller-WSE hybrid CHW plant, using a validated Modelica simulation testbed. A total of 27 fault scenarios representing nine common fault types were simulated and assessed using five energy and safety metrics and key operating measurements, for both representative mode-specific weeks and a full year. Results show obvious mode-depended energy impact: for example, a +2 ℃ bias in chilled water supply temperature sensor has negligible energy impact in WSE-only mode but causes a substantial increase in energy use in chiller-WSE hybrid mode. In contrast, negative supply air temperature sensor bias faults result in severe safety impacts across both modes. Annual analysis shows that extreme faults can increase energy consumption by up to 38.4% and leads to as many as 8115 unsafe hours. Collectively, the study results emphasize the necessity for developing fault-tolerant control strategies tailored to hybrid CHW systems and provide critical insights to guide their design and implementation.