Fault Detection and Diagnostics for Rooftop Air Conditioners

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normal _ value − current _ value
normal _ value
The normal value is predicted using an overall system performance model which
is built based on system manufacturer rating data. The model inputs are condenser inlet
air dry-bulb temperature and evaporator wet-bulb temperature.
The compressor overheat degradation is defined by,
current _ Tdis
− normal _ T
max_ ∆T
dis
dis
The maximum
∆ Tdis
is found to be around 40 F by Chen’s data (2000), which
should be confirmed by more investigation. There is difficulty to predict normal values
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.
4.2.2.4 FDD Report Window (FDDRW)
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.