By Bob Baker

I visited a one-year-old school last Thursday and when we entered the gymnasium, it was clearly uncomfortable. The temperature was a normally comfortable 74 degrees. The humidity, however, was just above 70%. This was high enough to make it a little uncomfortable. Fortunately, there was not any evidence in this case of odors, mold growth or other signs that the elevated humidity had led to an IAQ problem.

You may be thinking that my experience was not all that unusual. It is kind of normal to find a slightly elevated humidity level on a humid, mild temperature day here in Florida in a large unoccupied space. There just is not enough of a cooling load to cause the system to operate for a long enough time to pull moisture out of the air. Normally, such a situation will not cause problems because as soon as the space is filled with people, the heat load will push the system to remove the excess moisture as well as provide cooling.

Humidity - a universal problem

One interesting thing about this school was that it was not in hot/humid Florida. It was in Lafayette Indiana, a location clearly not in the "humidity belt". In spite of a commonly held belief that humidity problems are confined to coastal area and the south, humidity and the problems it brings can be a challenge in any area. Another was that we were not there because of the humidity problem. We were there to address a customer complaint. I was the guest of a sales representative and local distributor for a well-known air filter manufacturer. They had recently taken on the school district as a customer and this location had a complaint. The janitor had found feathers and straw in the air handler. He thought the new filters were defective.

As son as we opened the air handler, the cause of the humidity problem was clear. The face of the chilled water coil was completely covered by trash. The coating consisted of grass, feathers, straw, lint and other materials that even a low efficiency filter should have removed from the air stream. As we have discussed in past issues, even a small amount of change in airflow through a cooling coil greatly affects its ability to dehumidify air. In this case, the restriction was so great that the system operation was greatly affected. The humidity problem had been noticed but was blamed on chilled water that was too warm because of energy conservation measures in place at the school.

Small Change big impact

Clearly, there was a filtration problem. On closer inspection, the cause of the problem was clear. The filters were not tight enough and the incoming air was passing around the end of the filter. The system had used 2 inch pleated filters that were slid into a rack. At the end, a spacer had been fabricated to fill a two inch gap between the last filter and the access door. As an economy measure, the school had changed to a ring panel supporting deep loading polyester media. This is an option utilized by many locations today. When the support rings had been ordered, they were ordered for the same size as the filter cartridges they were replacing. When the filter media was installed, however, it was cut for the full width of the filter track and the spacers that had been used to fill the end space were discarded.

The filter rack appeared to be full from side to side. The edge of the media however was not supported because the support ring was short by the same distance as the previous cartridge filters. When the fan was in operation, the pressure of the incoming air caused the media to fold over on the end. This opened up a small gap of about a half an inch. This large a gap will allow most of the airflow to bypass the filter. Air will find the route of least resistance. In this case, all of the trash carried in from the outside air inlet just upstream from the filter bank was carried around the filter and deposited on the coil surface. Very little of the air was being filtered.

The spacers could not be replaced because they would not work with the ring panel arrangement. In this case, a simple solution was to cut a piece of duct liner and glue it to the inside of the filter access door. This effectively filler the gap yet represented a convenient fix.

This experience reminded me of the large impact that even a small amount of air bypassing the filter can have. Closely inspect your installations. If the filters do not fit tightly without gaps, make adjustments or rebuild the filter racks. Your customers' air quality will be better for your effort. In addition, you will find that coils are easier to clean without all the lint buildup.

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.