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Is Mold A Winter Problem?
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Down here in south central Florida right now it is about as winter as it gets. A lot of nice days; some cool (in 40s). Humidity is about as low as we see it, which is still high for much of the country (normally above 60%). For much, if not most of the rest of the country, however, things are a good bit different. Temperatures stay below freezing for weeks on end and humidity is well below 50% virtually all of the time. As a result, mold growth is not a concern for most of us at this time of year. Or is it?
We have learned that growth of bacteria and mold is very rapid when humidity is above 60% and it is warm. Here in Florida we see dramatic evidence of this during the summer. Mold grows on the sides of our buildings, sidewalks, plants, and almost everywhere exposed to the heat and humidity during the summer. At this time of year, we can relax and not clean our patio furniture and other outside surfaces so often. Growth has slowed down if not totally stopped.
Growth Inside the Air Handler
Many interior environmental surfaces and components consist largely or entirely of organic materials that serve as ideal food sources for bacteria, mold and other fungi. Heating, ventilation and air-conditioning ("HVAC") systems generate moisture that feeds such growth and the interiors of these systems provide an especially favorable environment where microbial growth can expand uncontrollably into colony form units.
Inside an HVAC system, humidity is not as important as dew point. A cooling coil can take the air stream to dew point regardless of the humidity level. Cooling coils are perhaps the most contaminant-prone component of an air-handling unit. When operating, they are generally wet and relatively warm. Under most circumstances, coils collect more than enough airborne particulates to make nutrients readily available in the type of warm, moist environment that's ideal for pathogen growth.
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When mold colonies grow, they produce a sticky substance called enzyme mycelium, which traps dust particles from the air and breaks down the trapped particles into food. By preventing the growth and establishment of colonies from biological contamination in HVAC systems, you can effectively eliminate the various health effects caused by microbes in the HVAC system. Good Industrial Hygiene is a major issue in our industry and microbial growth in HVAC systems is problematical for several reasons:
- It damages and disfigures surfaces where it grows.
- Waste products secondary to its growth are a source of noxious odors.
- Some microbial growth is pathogenic (disease causing).
- The organisms and their spores trigger undesirable immune system responses in humans.
- Microbial growth on coils acts as an insulator that interferes with heat transfer.
Growth Is Low In The Winter
It is a generally accepted fact that growth of all microorganisms including mold is much slower with cool dry conditions. When we first started marketing mold growth control products for HVAC systems, we accepted this fact and did not expect much demand outside of the so called "humidity belt". To our great surprise, there was and continues to be great demand for our products in Colorado, Illinois, Wisconsin, and Indiana which are generally thought of as areas where microbial growth is not a problem.
All of our customers cite concerns for health and comfort caused by mold and bacteria in indoor air as their main reason for using growth control products. In the case of northern customers, however, their concerns normally are related to actual tests that show what seems to be an excessive level of organisms. These tests are what lead to the buying decision. Here in the south, in contrast, mold control is more likely to be a normal part of system maintenance. The problem is so obvious that control measures are accepted as normal.
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Thus it has begun to appear to us that the problems are not related to climate. They are universal. The difference is that humidity belt residents are more prepared to recognize the problems because of the conditions they see outdoors every day. So, if mold is such a universal air quality problem, why haven't we heard more about it?
The IAQ/Health Debate
Until very recently, indoor air quality has not been considered a health matter. Poor indoor air quality was seen as something that could be distracting, uncomfortable, and lead to low productivity. It was not seen as a threat to health except in the most outrageous cases. As a result, little research was done to better understand the role of microbial growth and indoor air quality problems. It was felt that if growth were important, health would be more of an issue because microbial growth clearly can affect health.
When work first started in ASHRAE committees on revisions to Standard 62, a question posed early on was what effect, if any, poor indoor air has on health. Eventually this became one of the most important debates involved in updating the standard. As the topic was discussed, it soon became apparent that most experts believed that poor indoor air quality has a very negative effect on health. Some even called for the standard to become a health standard rather than just ventilation standard. Everyone conceded that there is little that is helpful in the present research literature.
The debates that have taken place have led to new research that is producing some interesting information. It adds to our belief that growth is a major cause of IAQ problems. Research that will conclusively demonstrate the relationship between biological air contamination and health is complex and time consuming, however. Virtually everyone associated with IAQ believes there is a considerable linkage between health and microbial growth.
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The only question is whether the health effects are limited to allergies, colds, and other temporary conditions or are they more permanent and debilitating.
Winter and Cool Climate Growth
So, the answer is, Yes! There is growth during the winter and in cool climates that causes problems in HVAC systems. This is because the inside of the HVAC system has a climate of it's own that is independent of either the outdoors or the building the system serves. The introduction and removal of heat, humidity and creation of rapid air movement through the system creates a microclimate that can be quite different from the outside air conditions. This climate system also changes from hour to hour, creating conditions within the air handler and ducts that alternately promote microbial growth.
When humidity is low, which is typical during the colder, dryer months of the year, these microbial colonies go into survival mode and emit tens of thousands of spores, which can contain mycotoxins. These spores are then breathed into the lungs, which can cause upper respiratory infections and trigger the immune system to release histamines in humans. This could explain many of the symptoms of stuffy sinuses and runny noses that cause misery during the cooler winter months.
With proper maintenance, these continuous mini climate changes will not lead to excessive growth. More often, the result is a buildup of increasing levels of contamination until it reaches a concentration that causes problems. More and more contractors are finding that in order to maintain an acceptable level of indoor air quality (and possibly health) for their customers, they need to include the prevention of growth as part of their maintenance offering. Those services must be included year round because the mini climate inside the HVAC system has winters and summers independent of those of the outside world.
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Bob Baker is the author of a book, Hospital Engineering, Facilities Management Engineers Role in the Contemporary Infection Control Program, and has developed numerous papers and presentations. Baker has lectured extensively on indoor air quality, consults with businesses on their indoor air quality needs, and is the author of a book entitled Indoor Air Quality: An Introduction for HVAC Contractors. He also authors and publishes an informative bulletin entitled MicroNews on the effect of microbial contamination and bioaerosols in air-conditioning, humidifying and cooling systems.
Bob is a member of the American Society of Heating Refrigeration and Air-conditioning Engineers (ASHRAE) where he is a member of TC 9.8 (Large Building Applications) GPC4 (Operations and Maintenance) and GPC17 (Particulate Measurement). He is also a member of ASTM committee D22.05 (Indoor Air Quality).
Bob Baker is the Chairman and CEO of BBJ Environmental Solutions, Inc., a manufacturing company specializing in providing clean air through environmentally responsible products, such as BBJ MicroBiocide, BBJ Micro Coil Clean, BBJ Spray Disinfectant/Cleaner, and Fresh Duct Odor Eliminator. 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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