Fault Detection and Diagnostics for Rooftop Air Conditioners

78
Figure 4-25 plots the normalized fault indicator for a condenser fouling fault. It
can be seen that most of the steady-state data points (>95%) are at the right of the FDD
threshold and the mean value is about 0.5, which indicates that the condenser is a little
dirty. If this fault happened individually, it would result in about 10% cooling capacity
degradation.
Figure 4-26 plots the normalized fault indicator for a compressor valve leakage
fault. It can be seen that all the steady-state data points are at the left of FDD threshold
and the mean value is about -0.7, which indicates that the compressor works properly and
the compressor has about 15% heat loss. However, according to heat transfer analysis and
our experience with laboratory data, compressors installed in York and Trane RTUs have
very small heat, less than 5% of the power input and even gain some heat at some
operating conditions. The explanation for this discrepancy is probably that the discharge
line temperature is not measured accurately using the RTD temperature sensor.
Deliverable 2.1.5 discusses the RTD measuring issue and presents a correction approach.
However, Figure 4-26 shows that the discharge line temperature is not corrected
accurately as well, which is because the sensor is not installed properly.
Figure 4-25 Histogram bar plot of the normalized fault indicator for condenser fouling