There are a variety of factors that contribute to mold growth in HVAC systems including high ambient humidity/dewpoint levels, indoor humidity levels, condensation, and lack of HVAC maintenance. Here are some items to keep an eye on year round that will hopefully keep this problem from occurring in your work place or home.
High Interior Humidity: Humidity control tends to be the leading contributor to unwanted growth in your AHU's and associated ductwork. Interior humidity levels should be monitored on an annual basis and always during extreme heat conditions when the levels are the highest. Properly working dehumidifiers, dryer vents, bath, and exhaust fans can certainly help with maintaining normal levels. On the contrary, improperly functioning ventilation systems will contribute to the problem.
Many commercial building, schools, and hospitals use in-system or automatic humidifiers to help maintain constant humidity levels, especially during the winter months. While these are great when they work, it is not uncommon for mechanical valves and solenoids on these devises to corrode in the open position and continually humidify the air regardless of the thermostat set point.
When extreme interior humidity levels are present, the moisture droplets get circulated through the HVAC system and attach themselves to dust and debris in the ductwork. In just a short time the extra moisture will use this debris as a food source and start growing inside the system as it would on carpet, drywall, or other porous interior building surfaces.
Condensation: When your cooling systems are running, condensation is created to help remove humidity from the air. During extreme exterior high humidity and high dewpoint conditions, these AHU and RTU coils struggle to keep up with the humidity to condensation differential. This excess moisture begins to attach itself to the interior debris in the AHU's, fan housings, and ductwork, causing the unwanted growth to begin as mentioned above. This is a phenomenon to keep an extra watch out for during summer months.
System Maintenance: Here are some HVAC maintenance tips that can reduce the chance of an unwanted flower bloom in your HVAC system
- Schedule annual system inspections with your HVAC contractor to ensure everything is mechanical functioning properly
- Inspect your AHU drips pans and drains to ensure they are working properly
- Have your AHU's, coils, and ductwork cleaned on a routine bases (every 3-5 years) by a NADCA Certified Duct Cleaner to remove the source contaminants that become the food source and breeding ground for growth
- Ensure humidifiers are properly functioning
- Be disciplined with your filter changes