Project Report

Persistence #3A:
An Assessment of Technical Degradation Factors:
Commercial Air Conditioners and Energy Management Systems

CADMAC Report # 2028P
Prepared for: CADMAC Persistence Subcommittee:
     Paciflc Gas and Electric, San Diego Gas & Electric, Southern California Edison, Southern California Gas
Report dated: February 25, 1999
Prepared by Proctor Engineering Group
Contributor: George Peterson, P.E., Rob dekieffer, John Proctor, P.E., Tom Downey

Executive Summary

Commercial DX AC

High efficiency commercial package air conditioners can attain efficiency gains through a variety of means: changing to a scroll compressor, changing the metering device, changing motors, adding face area, and adding rows of coils. In Persistence I no relative degradation was likely from the above means except for adding rows to the coils. Due to this, the TDF was determined to have a high degree of uncertainty. There are no technical data available that assist in establishing the differential rate of fouling or efficiency loss.

Research Methodology
Proctor Engineering Group established a time series estimate for condenser and evaporator coil fouling rates. This was derived from available research. Laboratory testing was used to modify the estimated fouling rates and establish a profile for coil fouling. Both high efficiency and standard efficiency coils were tested in a controlled laboratory environment and subjected to continuous fouling. The efficiency of the air conditioner was monitored at various intervals to document the effects of coil fouling on efficiency.

Research Study Results
All of the coils exhibited the same basic fouling behavior. The predominate site of coil fouling was on the face of the coil. The reduction in efficiency was due to the reduction in air flow across the coil. The reduction in air flow on the evaporator coil tended to reduce capacity more than efficiency. The opposite was true for air flow reductions on the condenser coil.

When the air flow was reduced slightly, there was a commensurate reduction in efficiency. As the fouling reached critical proportions, the rate of air flow reduction was greatly accelerated and the efficiency and capacity dropped accordingly. Air flow was reduced 35% on the high efficiency coil with a 2% drop in EER. When air flow was reduced 35% the standard coil had under a 6% drop in EER. The majority (4.6%) of that reduction came in the last two years of the twenty year projection.

Due to the length of time required in the fouling process, it was difficult to control for the amount of contaminants reaching the coils. Physical investigation of the coils and evaluation of the fouling profiles were used to confirm that the number of rows in the coil did not have an impact on the fouling rate.

The efficiencies of both systems were insensitive to low and moderate amounts of air flow reduction due to fouling. However, the high efficiency coils were less susceptible to efficiency loss due to high reductions in air flow.

The condenser fouling data shows that fouling of the condenser coils has a much more dramatic effect on the efficiency. This is particularly true for the standard condenser coil. Although condenser coils have a better chance of being cleaned, fouling them has a more damaging effect on the efficiency and increases the power use of the equipment. A 35 % reduction in air flow resulted in a drop in the EER of 24 % for the standard unit and 19% for the high efficiency unit. The power use increased 18% and 13% respectively. The data indicate that efficiencies gained by increasing the number of coils are sustainable for up to 18 years, but that significant degradation of these efficiencies is likely after that. Still, the energy cost savings justify the initial extra expense to produce the units with more coils.

The testing shows that the TDF for this measure is greater than one.

Energy Management Systems

The billing data was analyzed in detail. The first analysis was site by site -- a case study approach. The final analysis brought together all the consumption data from all the sites and estimated the persistence of savings over time. The regression process provided statistically significant estimations at the 95% level.

Research Study Results
The research data showed that although there is some EMS savings degradation at some locations, other locations show increasing savings. The billing analysis confirms the field data that little or no degradation (diversified over all units in the study) exists. Some of the causes for this persistence are:

• No instances of disconnected or non-operational EMSs were found.
• The vast majority of EMSs appeared to be operated in a competent and professional manner.
• EMS operators had found that the EMS was a useful tool in performance of their jobs.

Technical Degradation Factors
Establishing Technical Degradation Factors was the primary purpose of this research. A technical degradation factor (TDF) was estimated for each measure. These estimates are displayed in Table ES-1.

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