From concrete to wallboard to millwork, materials used to construct buildings absorb moisture. While a small amount of moisture is necessary for materials to cure properly and prevent cracking or distortion, excess amounts pose a variety of risks, including project delays, adhesive and coating failures, and mold growth. To prevent and combat moisture-related problems, contractors look to temporary climate solutions, such as heaters and dehumidifiers. By knowing which process is better for your application, your moisture control efforts will be more effective.
Humidity and Drying
In any drying application, the vapor pressure in the air and in the materials is what really matters. When atmospheric conditions are uncontrolled, molecules of water in the air apply vapor pressure on the materials they contact. Materials that absorb moisture do so at different rates until they reach an equilibrium moisture content, which is when they neither absorb nor release moisture into the air.
When a contractor implements effective climate control during construction, the moisture travels from areas with high vapor pressure to areas with lower vapor pressure. As a result, the affected materials desorb moisture vapor and release it into the air. If the building is under positive pressure, the mechanical drying equipment then pushes the moist air out of the space.
Heat versus Dehumidification
Basic psychrometrics tell us that heating the air does not change its moisture content (vapor pressure), only the air’s ability to hold moisture. Therefore, heating a building does not necessarily promote good drying. In fact, using direct-fired heat to heat a building will add moisture to the space as water is the biggest by-product of combustion. Direct-fired heaters pass the air directly through the flame before it enters the space, introducing water, carbon monoxide and other noxious gases. Direct-fired heaters can be effective during early stages of construction in cold climates where the vapor pressure is very low. This is only acceptable if the heater is bringing in air from outside the building. Direct fired heaters should never be recirculated as these harmful products of combustion can build up in the space.
Because heat is often necessary for the installation of some building materials, in-direct fired heaters can be a good addition to the climate control strategy. An in-direct air heater passes the air over a heat exchanger and exhaust from combustion is vented outside the building. These are designed to be placed outside the space but it is possible to recirculate the air as there is no contamination of the heated air. Again, it is always best to keep the building under positive pressure to allow moisture, VOCs and other vapors created in the construction process to be vented from the space. Electric heaters can also be considered if there is sufficient power available. These are simple, reliable and can be placed inside the building.
Dehumidification is a process that involves removing humidity, or water vapor, from the air. Dehumidification can be achieved by cooling the air or through the use of desiccants. The cooling and dehumidification process, or refrigerant dehumidification, uses a refrigerant to cool the air below the dew point temperature. The water vapor in the air condenses on the coil surface in the dehumidifier and drains away. In essence, the equipment removes humidity via condensation. This is often seen in a typical air conditioner, which is generally not capable of controlling humidity at a construction site.
Desiccant dehumidifiers, which are excellent for construction sites, contain hygroscopic materials that attract and hold moisture from the air that passes through the equipment. The equipment then releases the trapped moisture through an exhaust airstream. Desiccant dehumidification is very effective at lowering the vapor pressure in a space. In the end, you’re left with arid air that can dry the most saturated materials.
Construction drying solutions often combine heat and desiccant dehumidification because heat alone cannot reduce the vapor pressure in a space. The contractor and climate control provider should always use caution to avoid over drying when using heat and/or desiccant dehumidifiers. Many materials, such as joint compound and millwork can be damaged from rapid drying or from extremely low relative humidity.
To minimize your overhead costs, Polygon custom designs affordable construction drying solutions that include monitoring equipment, letting you track conditions and progress in real time. In addition to eliminating excess moisture from a site, forward-thinking contractors use the solutions from the start to create an environment that prevents high relative humidity levels and prevents project delays. Talk to a specialist at Polygon today to schedule a complimentary consultation regarding your construction drying needs.