Fault Detection and Diagnostics for Rooftop Air Conditioners

0.025
Indoor Conditions for Testing
Training Data
Test Data
0.80
0.020
0.60
0.015
64 F
0.40
0.010
55 F
58 F
61 F
0.20
0.005
0.000
60 70 80 90
T [F]
Figure 3.1 Indoor conditions simulated for training and testing steady-state models
The training data were gathered by running the rooftop unit with no faults. Data was
gathered over the course of three weeks of testing. To ensure that there were no faults
developing in the test unit over this time period and to test the experimental noise
which is present in the operation of the test unit, a test condition at T amb = 85 F, T ra =
76 F, Φ ra = 42% was retested every few days. The results of this repeatability test for
all of the measurements used by the FDD technique are shown in table 3.1. The most
noisy measurements, as expected, are the suction superheat and hot gas temperatures.
This level of experimental noise is already considerably above the measurement error
levels which were used in the steady-state analysis of the FDD technique performed
by Rossi. Figure 2.2 shows the level of suction superheat during the repeatability test.
The fact that the graph is not increasing during the test indicates that the level of
charge in the system is not decreasing, since suction superheat is particularly
dependent on the charge level in the system. One cannot expect to develop a model
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