Clean Coils, Energy and ???
Everyone knows that a coil with 0.05 inch of dirt, Biofilm, or other contamination buildup operates 32% less efficient. Or was that 42%? Or 5 microns? Or 23%. Oh well, why get hung up in the details. We have all seen the claims. They are posted on Internet sites, quoted in articles, and listed on slides in presentations. Most of us at one time or another have made reference to the efficiency savings that are possible if we keep coils clean. Although various references may quote different numbers, we really do not think too much about them because some level of savings just makes sense.
On today's high efficiency coils, any amount of buildup at all will restrict air-flow, probably cuts heat transfer efficiency, and just isn't the way things ought to be. The differences quoted by different references are probably due to differences in methodology that the various researchers who have studied the issue have used or local conditions or something else. Right? Seems right to me.
At least it did until a couple of years ago when Tom Yacobellis (who is the current President of the Indoor Air Quality Association) and I decided that it would be a good idea to find out what led to these different results and see if it might be worthwhile to do the work again and see which numbers are correct. Having made that decision, we began to ask anyone who posted, wrote about, or mentioned during a presentation energy savings related to clean coils, "Where did you get your data?"
Before very long we were going in circles. At least, the answers we were getting took us in circles. An author would tell us about a colleague who gave them the information who in turn would direct us to another source…until sometimes we ended back up with the person we started with. A number of times we were sent to the EPA web site (the reference has since been removed). No one there could identify a source or study.
Finally, we did locate a study that was done by the Louisiana State University Extension Service on three homes. Although the study reported up to 42% gain in efficiency, the impact of duct and equipment repairs was included in the results. In addition, a sample of three is not large enough for a solid conclusion. We agreed that we need better data if we are going to continue to discuss the energy savings that can be achieved by keeping systems clean.
Our findings led us to discuss the issue with a number of researchers during the ASHRAE meeting in Cincinnati in June of 1991. Dan Fisher from Oklahoma State University expressed interest in the subject. His interest led to a design class taking the issue on as a design project. They proposed to build a test apparatus designed to capture the operating parameters of a standard PTAC (Package Terminal Air Conditioner) unit like those used in many hotel rooms, apartments, and schools. There were several reasons for designing the test apparatus to work with these types of units:
- They are common so there is a ready supply of them to test for data development.
- They are easily accessible for testing, cleaning and repair if needed.
- They operate in a simple environment so outside variables are easily controllable.
- Units in any large facility offer a good mix of older and new units and clean and dirty units.
The project team designed, validated and completed construction of the apparatus during the first semester last year and traveled to Clearwater, Florida with Dr. Fisher for a field trial during the week before Christmas.
During the field trial, several units were logged while operating, removed and cleaned, then logging was continued for a like time. The number of units sampled during this trial was not sufficient for statistically valid conclusions. It appeared, however, from a cursory look at the data as it was being downloaded from the test apparatus that the device would be an extremely useful research tool. We are now in the process of arranging financing for Dr. Fisher to explore the following issues:
- Efficiency drop as units become progressively more fouled.
- Parallels between the potential for energy savings and the cost of preventative maintenance.
- Length of operational time before a unit becomes so fouled that efficiency is impaired.
- Effectiveness of various strategies for preventing contamination buildup.
- Usefulness of various operational parameters as early indicators of contamination buildup.
This has turned into an exciting project with considerable potential to provide new and useful information previously not available. We are looking forward to the future findings as this project moves forward. One thing is sure. The results of this work will provide a lot of factual support for keeping systems (and especially coils) clean.
November 30, 2002
Mr. Baker's field of expertise is the control of contamination in air-conditioning and ventilating systems by mold, mildew and bacteria. He writes and speaks frequently about the efficacy, legal risks, and regulatory issues involved in various control strategies. He serves on ASHRAE Technical Committee TC 2.3, TC 2.4, TC 9.8, and Sampling of Airborne Particulate Concentration in Commercial and Residential Buildings GPC 17P. He also serves as a member of ASTM D22.06 (Indoor Air Quality) and is on the Board of Directors of the Indoor Air Quality Association and the Florida Public Health Foundation. Because HVAC applications encompass new uses from an U.S. EPA regulatory standpoint, Mr. Baker works closely with the EPA and industry groups, including serving as the chair of the IAQ committee of the Consumer Specialty Products Association, to help formulate policy in this area.
Bob Baker is Chairman and CEO of BBJ Environmental Solutions, Inc., a company specializing in providing clean air through environmentally responsible products, such as BBJ MicroBiocide , BBJ Micro Coil Clean , "FreshDuct Odor Eliminator ", and BBJ Mold and Mildew Remover™ as well as the revolutionary new Power Coil Clean™. For additional information, Mr. Baker can be reached at (800) 889-2251 or through the company web site at http://www.bbjenviro.com.
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