Dehumidification
Dehumidification is the mechanical removal of water vapor from the air inside a drying environment, capturing the moisture that evaporates from wet materials so it cannot redeposit elsewhere in the structure.
The Role of Dehumidifiers in Drying
Dehumidification is one half of the drying equation. Air movers drive evaporation, pushing moisture from wet materials into the air. Dehumidifiers then remove that moisture from the air. Without dehumidification, evaporated water simply raises the humidity of the drying chamber and redeposits onto cooler surfaces, potentially causing secondary damage and even mold in previously dry areas.
A properly designed drying system balances these two functions. If airflow outpaces the dehumidifiers' capacity, indoor humidity climbs and evaporation slows across the entire space. Matching dehumidifier capacity to the size of the affected area, the water class, and the number of air movers is a core competency governed by IICRC S500.
Refrigerant Versus Desiccant Dehumidifiers
Two main technologies are used in restoration:
- Refrigerant (LGR) dehumidifiers pass humid air over cold coils, condensing the vapor into liquid that is drained away. Low-grain refrigerant (LGR) units add a pre-cooling stage that lets them keep working at lower humidity levels than standard units. They perform best in warm, moderately humid conditions.
- Desiccant dehumidifiers use a moisture-absorbing wheel or medium and are effective at low temperatures and very low humidity, where refrigerant units lose efficiency. They are often chosen for large commercial losses or for drying dense materials like hardwood and plaster.
The choice affects how quickly the space reaches a favorable grain depression, the measured difference in moisture content between the air entering and leaving the machine.
Measuring Dehumidifier Performance
A dehumidifier's effectiveness is verified, not assumed. Technicians measure the temperature and relative humidity of the air going into the unit and the air coming out, then use psychrometry to calculate the grains of moisture per pound of air removed. A healthy grain depression confirms the machine is actively pulling water out of the environment.
These readings are recorded on the daily moisture log alongside moisture meter readings from the structure. Together they tell the story of the dry-out: the structure's moisture content falls while the dehumidifiers demonstrably capture the water being evaporated. This documentation is central to a defensible water damage restoration claim.