Fault Detection and Diagnostics for Rooftop Air Conditioners

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1. Planned preventive maintenance service savings, which are about $2,000 for
each RTU.
2. Operational cost savings, which include two parts: utility cost and equipment
life savings. The utility cost savings should include both energy and peak
demand savings. However, more work is needed to evaluate the peak demand
savings effect.
3. Fault detection and diagnosis savings, which include two parts: unnecessary
service savings and fault diagnosis savings.
4. Smart service schedule savings.
The last three items are difficult to quantify, because they are related to the rate of
occurrence and level of faults. As previously mentioned, around 60% of packaged
systems in California are improperly charged. According to our initial investigation of
California field sites, fifteen of the twenty-one systems (71%) are impacted by faults,
eleven of them (52%) are impacted by filter/drier restrictions, ten of them (48%) are
impacted by refrigerant charge faults, and eight of them (38%) are impacted by both low
charge and filter/drier restriction faults.
In order to quantify the net savings, the following conservative assumptions were
made:
1. 10-year equipment life under normal operating conditions.
2. No replacement of major components, such as the compressor and fan motors
during the life of the equipment.
3. On average, the performance of the system is assumed to be degraded for 40%
of its lifetime with an EER and cooling capacity degradation of 21% and 30%,
respectively.
4. One coil cleaning service can be saved per year through automated FDD.
5. A 60% probability that a refrigerant charge fault will occur once during the
equipment lifetime.
6. A 60% probability that a filter/drier restriction fault will occur once during the
equipment lifetime.