Fault Detection and Diagnostics for Rooftop Air Conditioners

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2.2.1.1 Normal Operation Data
The normal operation data set was obtained at a number of controlled normal
operating conditions. There are two sets of normal operation data. A large set of data was
gathered at combinations of indoor dry bulb temperatures ( T ra
) of 70, 73, 76, 79, and 82
F, indoor wet bulb temperatures ( T
wb
) of 33, 38, 61, 64, and 67 F, and ambient
temperatures ( T amb
) of 60, 70, 80, 90, and 100 F. A smaller set of data was gathered at
indoor dry bulb temperatures of 71.3, 74.3, 77.3, and 80.3 F, indoor wet bulb
temperatures of 36.3, 39.3, 62.3, and 63.3 F, and ambient temperatures of 63, 73, 83, and
93 F. The conditions were selected because they completely cover the normal comfort
region defined by ASHRAE (1993).
To ensure that there were no faults developing in the test unit during the test
period and to quantify experimental noise which is present in the operation of the test unit,
a test condition at T amb
= 83 F, T ra
= 76 F, T wb
= 61 F 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 2-1. Because of the smaller heat capacity associated with vapor (as
compared with liquid), the noisiest measurements are the suction superheat and hot gas
temperatures.
Table 2-1 Repeatability analysis during steady-state model testing
Data
(deg. F)
Tevap
Tsh
Tdis
Tcond
Tsc
∆Tca
∆Tea
Mean 43.76 8.42 193.11 108.69 7.03 11.72 19.14
Std. Dev. 0.39 1.73 1.23 0.40 0.23 0.09 0.17
Spread 1.21 4.80 4.04 1.28 0.60 0.26 0.64
2.2.1.2 Faulty Operation Data
In addition, five types of artificial faults were introduced at different fault levels
and the unit was tested at different load levels in order to evaluate the performance of the
FDD technique.