Fault Detection and Diagnostics for Rooftop Air Conditioners

55
2.1.2 Condenser Fouling Decoupling
Figure 2-2 gives the condenser air mass flow rate estimated using a virtual sensor
under different fault types with different fault and load levels. In order to show the
potential of the decoupling scheme, this virtual sensor uses the actual refrigerant mass
flow rate measurement. From 2-2, it can be seen that the condenser air mass flow rate is
only influenced by the condenser fouling fault. The reduction of condenser air mass flow
rate is proportional to the condenser fault level and independent of load levels and other
faults. So full decoupling between condenser fouling fault and other faults is achieved.
Condenser Air Mass Flow Rate
(lbm/hr)
20000
17500
15000
12500
10000
evapfoul condfoul refleak llrestr compnv
Load level 1 Load level 2 Load level 3 Load level 4 Load level 5
1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5
Fault Level
Figure 2-2 Decoupling condenser fouling fault using measured refrigerant mass flow rate
A refrigerant mass flow rate meter is too expensive for this application, so it is
estimated using compressor map data. Figure 2-3 shows the condenser mass flow rate
estimated using a refrigerant mass flow rate estimate under different fault types with
different fault and load levels. It can be seen that the condenser mass flow rate estimate is
influenced simultaneously by condenser fouling and compressor valve leakage with
inverse directions. The dependence on compressor valve leakage is caused by errors in
refrigerant mass flow rate prediction, since the compressor map was built using normal
55