Even when small amounts of water are allowed to accumulate on the surfaces inside a building, the resulting moisture and mold problems can be costly. Mold and fungi can lead to air quality problems and sick building syndrome while condensation can lead to structural damage. Understanding the causes of moisture buildup is the first step in finding the right control solution.
Relative humidity and condensation
Temperature affects humidity, which is the amount of water vapor in the air. Relative humidity is the amount of water vapor in the air compared to how much moisture the air can hold at that temperature. Warm air can hold more moisture than cold air. The dew point is the temperature at which air can’t hold any more moisture. As the temperature decreases, condensation accumulates on colder surfaces, such as walls and windows.
The humidity level in a building can vary. If moist air is removed to another area where a drop in temperature occurs, condensation may result. The first strategy for reducing condensation is uniform air temperature control; another is to remove the moisture. Desiccant materials and duct heaters can effectively remove moisture from the air, lowering relative humidity. The moisture can then be dispersed through ventilation or redirected to other areas of the facility where moisture is needed.
If relative humidity reaches 70% at warm temperatures, mold growth can occur. This often happens in poorly heated or ventilated areas. The following strategies will help control growth:
- Reduce humidity.
- Improve air circulation.
- Increase insulation levels.
- Improve background heating.
Temperature and humidity control
Mold and mildew are commonly found on the surface of exterior walls or behind wall coverings. A room with an exposed corner is typically colder than adjoining rooms, becoming a potential site for condensation. If mold and mildew growth are found, the relative humidity at the room’s surface is likely to be above 70%. If the problem is temperature related, add insulation or improve heat flow to increase the temperature of cold surface areas.
If the relative humidity at the increased temperature is higher, control strategies should focus on decreasing moisture content. Solutions for reducing relative humidity levels include:
- Control surface vapor pressure to prevent warm outside air from contacting colder interior finishes.
- Relocate ducts and diffusers to eliminate cold spots.
- Maintain vapor barriers, facing sealants and insulation regularly.
- Increase the room temperature to avoid overcooling.
Cooling humid air is expensive because the water changes from vapor into liquid condensate, releasing heat. Many facilities, such as restaurants, are often overcooled during the summer to maintain comfort. In these cases, a more economical option is to first reduce the moisture content in the air using desiccant dehumidification.
Desiccants are materials that naturally absorb moisture, like activated alumina crystals, silica gel and lithium chloride solutions. In a liquid system, the solution is sprayed into the incoming air, removing the moisture. In a dry desiccant system, a rotating wheel containing solid desiccants dehumidifies outside air continuously as it enters the cooling unit.
Desiccant systems are very efficient and their use is well-established in applications such as ice arenas, hospitals, supermarkets, schools and restaurants. The higher installation and maintenance costs of desiccant systems are offset over time through energy savings and lower utility bills.