Fault Detection and Diagnostics for Rooftop Air Conditioners

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3.3 Results
Table 3-2 gives comparative results for the two methods in terms of FDD
sensitivity. Compared with the results obtained by Breuker and Braun (1998b), the
improved SRB FDD method has superior performance. Breuker and Braun (1998b)
presented results in terms of a “1 st Detected” and “All Detected” level. The “1 st Detected”
level is the level at which the fault was first successfully detected and diagnosed
throughout the data set. The “All Detected” level is the level at which the fault was
detected and diagnosed during all steady-state operating conditions. As an example, the
“1 st Detected” refrigerant leakage fault level is 3.5% for the improved method and 7.8%
for the original SRB method, whereas the “All Detected” refrigerant leakage fault levels
are 7% and 9.5%, respectively. Similar results occur for the other faults. The results of
Breuker and Braun do show some “1 st Detected levels” that are below the lowest level of
fault that was introduced. This is because their results were calculated by interpolating
the impact of the fault level. This was not done for the current study. For a direct
comparison without interpolation, the original SRB results should be rounded up to the
next discrete fault level (shown in parenthesis for each fault type). For example, the “1 st
Detected” refrigerant leakage fault level for the original SRB, 7.8%, would be rounded up
to the next discrete fault level, 10%. With this fairer comparison, the improvements in
performance with the new method are more dramatic.
Table 3-2 Performance comparison of previous and improved FDD method
Refrigerant Liquid-line Compressor Condenser fouling Evaporator
FDD leakage restriction valve leakage (14.6,29.2,41.4,56.1)% fouling
results (3.5,7,10,14)%(5,10,15,20)%(7,14,19,28)%
(12,24,35)%
1 st All 1 st All 1 st All 1 st All 1 st All
Original
SRB
7.8 9.5 6.2 8.1 6.5 14.2 11.6 15.1 11.1 30.9
Improved
SRB
3.5 7 5 5 7 7 14.6 14.6 12 12