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Today's tip focuses on how relative humidity, both too high and too low, can have a negative effect on indoor air quality. In general, the sweet spot for humidity is somewhere between 30 and 60 percent relative humidity.
Don't operate your building at low relative humidity. One of the most irksome contributors to poor IAQ, especially in wintertime, is low relative humidity. Lowering the temperature in the occupied spaces is one practical way to improve this situation.
When the relative humidity in commercial and institutional buildings is low, occupant's mucous membranes in the nose, mouth and throat dry out. The result is they become much more sensitive to the ubiquitous pollutants found in an indoor environment. More cases of colds, allergies, and even nosebleeds are not uncommon.
The solution to this problem is difficult. Installing a central humidification system into the building's air handling system is often impractical and cost prohibitive. Individual space humidifiers can help, but they have stringent maintenance requirements which, if not adhered to, can present IAQ problems of their own.
But don't go overboard and make the mistake of operating your building at high relative humidity either. High humidity provides conditions for microbial growth. If high relative humidity conditions are a problem at your facility, consider using dehumidification equipment. You can also consider the use of high limit humidifier controls to prevent condensation on the inside surfaces of the downstream duct. Lastly, consider using unlined ductwork with external insulation directly downstream of the humidifiers or cooling coils to help prevent microbial contamination.
You can refer to ASHRAE Standard 55, "Thermal Environmental Conditions for Human Occupancy" for more detail on acceptable ranges for humidity.