Heating, Ventilation and Air Conditioning (HVAC) systems are installed in commercial buildings to meet the actual demand of heating and cooling at a given time such that the thermal comfort of occupants within the rooms (or zones) can be ensured. This is achieved by feeding air into the zones at a constant temperature using variable air volume (VAV) boxes, which offers an energy-efficient solution for a multi-zone building. The amount of supply air is controlled with the help of dampers located within the VAV boxes. Any occurrence of a fault in VAV dampers may cause undesirable results such as discomfort to occupants and a loss in energy efficiency. In this paper, we propose a nonlinear observer-based fault diagnosis method to extract a precise information about the fault so that subsequently, the controller can take corrective actions ensuring the thermal comfort of the occupants. The novelty of this method lies in its simple construction, which makes it applicable for diagnosing a wide variety of actuator faults in HVAC systems. The effectiveness of the proposed method is successfully demonstrated on a case-study of a one-storey building comprising of three zones, constructed using SIMBAD (SIMulator of Building And Devices).
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