Fault Detection and Diagnostics for Rooftop Air Conditioners

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Figure 2-27 Histogram bar plot of the continuous running time between off-cycles of the
RTU
In addition to the comfort criteria, Figure 2-28 plots an economic criterion, EER
degradation. It can be seen that the system EER degraded about 10~40%, which depends
on the operating conditions. Compared with the cooling capacity degradation, the EER
degradation was a little smaller. This is because the power consumption was reduced a
little but less than the degradation of cooling capacity when the refrigerant mass flow rate
was reduced due to faults. Figure 2-29 plots the system power consumption reduction.
The average power consumption reduction is about 15%, which is smaller than the
average cooling capacity degradation of 32%. In sum, the average EER degradation is
21%, which is a pretty large economic loss. Since costs to recover the system charge,
replace the filter or drier, and clean the condenser are not expensive, service to correct the
faults is justified.
In summary, from both comfort and economic criteria, it is justified to correct the
diagnosed faults as soon as possible.
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