Fault Detection and Diagnostics for Rooftop Air Conditioners

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for T
dis
because there is no overall system state model available. For this demonstration,
it is assumed that the system driving condition is not changed much and the measured
value at the fault free condition is used as the normal value. Further research should be
done later to find an inexpensive safety indicator for a compressor.
2.2.4 FDD Report Window
To help customers make a decision whether to service the diagnosed fault or not,
the FDD Report Window generates a tabular report for the FDD results including
diagnosed faults and relative severity indicators and system performance and safety
degradation indices, and provides an FDD recommendation. In this demo, the FDD
recommendation is based on performance and safety degradation. If the performance
degradation is over twenty per cent or the compressor is overheated up to ninety per cent,
service is recommended. More investigation is needed for fault recommendation.
2.2.5 Output of the FDD Demonstration
This section provides sample outputs of the FDD demonstration after each fault
was added and removed (watch the movie for details).
Figure 2-13 captures a movie frame when the system was running at low
refrigerant charge (step 1 of section 2.2.1). The “Fault Detection and Diagnosis window
(FDDW)” indicates that there existed a refrigerant low charge fault whose fault severity
was around 0.45. The “System Performance & Safety Degradation Window (SPSDW)”
plots the overall degradations, all of which were less than 20%. The “FDD Report
Window (FDDRW)” summarizes the indicates and generates the FDD report table and
recommended that “although there is (are) fault(s) with minor impacts on overall system
performance, it may be not worthwhile to service so far”.
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