Seasonal Drying Challenges

Controlling humidity is paramount when drying water-damaged structures. This is achieved by deploying dehumidifiers to remove excess humidity. This principle also applies to mold remediation projects, especially when residual wet building materials remain after demolition of porous materials.

The amount of dehumidification required is a complex calculation that must account for a project's location and the current season. These external factors significantly influence the psychrometric properties of the air. Psychrometrics is the study of the physical and thermodynamic properties of a gas-vapor mixture, like the air we breathe.

Understanding Seasonal Humidity Loads

During the summer months, much of the country experiences hot and humid conditions, with the exception of arid regions like the southwestern United States. Whereas in the winter, the air is typically cold and dry due to lower temperatures causing reduced evaporation outdoors.

This contrast is vital because it dictates the direction of vapor pressure and thermal gradients. A gradient is a difference in a physical quantity (like pressure or temperature) between two locations. The Second Law of Thermodynamics governs the movement of heat and moisture, stating that both will naturally move from an area of higher concentration to an area of lower concentration.

• In the winter (heating season), the building's interior is warm and more humid, while the exterior is cold and dry. This creates a powerful gradient where heat and moisture move from the indoor environment toward the outdoors.

• In the summer (cooling season), the opposite occurs. The exterior is hot and humid, and the conditioned interior is cool and dry. Consequently, heat and moisture attempt to infiltrate the structure.

Regardless of the season, these fundamental principles dictate that we must account for the exterior conditions, which directly impact the dehumidification load.

Mitigating Seasonal Challenges

In the summer, we often have to compensate for the additional humidity load imposed on our drying equipment. This challenge is frequently compounded when we open the building envelope to remove saturated, porous materials like drywall and insulation. The building envelope is the physical separation between the conditioned interior of a building and the unconditioned exterior.

Conversely, in the winter, we may need to supplement the existing heating system. While the removal of wet materials helps with moisture reduction, it also exposes exterior walls to cold air, increasing heat loss.

According to the IICRC S500 standard, a building's external conditions can reduce the need for dehumidification by up to 20% or increase it by as much as 60%.

The Importance of Heat in the Drying Process

A low humidity ratio (measured in grains per pound of dry air) doesn't automatically mean a successful drying impact. The humidity ratio, or mixing ratio, is the mass of water vapor per unit mass of dry air. You must also provide sufficient heat to facilitate evaporation. Evaporation is the process by which a liquid turns into a gas.

Furthermore, refrigerant dehumidifiers have an optimal operating range, typically between 70−90∘F. Operating them outside this range, especially in cold conditions, significantly reduces their efficiency. Remember, cold grains do not dry.