Fault Detection and Diagnostics for Rooftop Air Conditioners

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performance is realized. According to Breuker’s (1998a) investigation, cooling capacity
and COP only degraded 6.1% and 10%, respectively when 35% of the condenser area
was covered. Cleaning a condenser coil and replacing an evaporator filter costs about
$120 per service and is typically done twice a year. If automated FDD were applied,
service could be based upon a quantitative assessment of the impact and unnecessary
service could be reduced. If, for example, one regular service could be saved per year,
the savings would be $120 per year, which is significant compared to other costs.
5.3.2 Fault Diagnosis Savings (FDS)
Upon receiving an emergency call, a technician needs to go to the site, open the
system, and perform a diagnosis. Typically, service costs are calculated based upon a
charge for the visit (e.g., $115) plus an hourly rate (e.g., $65/hour). For example, to open
the system, check for refrigerant leakage and recover the system requires about four
hours. A four-hour service would cost about $375. There are three kinds of refrigerant
charge faults: refrigerant leakage, refrigerant low charge and refrigerant overcharge. The
former requires manual leakage checking, while the latter two could be diagnosed with an
automated FDD system. Furthermore, with the help of the automated FDD technique,
refrigerant could be added or removed without the requirement for recovering the entire
system charge, which is very time-consuming and costly. Table 5-4 lists the potential
savings for refrigerant charge faults associated with the use of automated diagnostics.
Table 5-4 Potential for Refrigerant Charge Fault Savings
Refrigerant
Charge Faults
Manual FDD
Costs Plus
Service ($)
Automated
Costs Plus
Service ($)
Savings ($)
Leakage 375 150 225
Low Charge 375 75 300
Over Charge 375 75 300