Analytical model based fault diagnosis method is seldom adopted for heating, ventilating and air conditioning (HVAC) systems as it is rather difficult to establish and verify an explicit model for HVAC systems. On the other hand, a flexible graphically based software called TRNSYS has been widely accepted in the design and optimization of HVAC systems recently. It makes sense to use TRNSYS to establish and verify an analytical model for fault diagnosis of HVAC systems. In this paper, a TRNSYS model of a HVAC system in multi-zone buildings is firstly established on the basis of practical data. Then, a state-space model of HVAC system is given according to the thermal-mass balance and air flow balance equations, and the consistency between the TRNSYS model and the state-space model is demonstrated. Also, some typical faults in the HVAC system are considered and the consistency between the two models under the faulty cases is verified again. Further, the effects of the faults on energy consumption is analyzed. The results show that some faults such as pipe scaling can significantly increase energy consumption while having no obvious change in room temperature. Based on the established models, some promising and challenging research directions for fault diagnosis of HVAC systems are finally discussed.
This paper presents an optimal diagnostic observer design scheme to deal with the remote fault detection problem for a local closed-loop system with unknown external disturbances and faults. To utilize limited network shared resources efficiently, an event-triggered generator is employed in the local closed-loop system to determine whether to transmit the current output measurement for fault detection. By constructing the error system that contains event-triggered transmission errors and evaluating the composition of the residual under the constraint of Luenberger conditions, the diagnostic observer which has optional order and flexible structure is designed by the use of factorization techniques to achieve the optimal performance tradeoff between disturbance robustness and fault sensitivity. Next, the inevitable influence of reference input on the residual is taken into account in the residual evaluation to deliver a time-varying threshold. Finally, a vehicle lateral dynamic system is presented to illustrate the validity of the proposed optimal diagnostic observer design scheme.
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