Air movement plays critical role in drying
January 1st 2006 Airmovers provide the high-velocity airflow that's vital to drying. In fact, effective drying requires the use of far more airmovers than dehumidifiers on a particular job comments Marcia Neu from Dri-Eaz
Airmovers serve two critical functions in drying: Airmovers remove the 'boundary layer' of wet air from wet surfaces. The boundary layer is a region of high humidity near a wet material.
A boundary layer hinders evaporation which acts as a vapour barrier.
Although the ambient air in the structure may be relatively dry, the layer of air next to a wet surface can be quite humid - potentially even at saturation. Airmovers remove the boundary layer by rapidly supplying drier air directly to the wet surface and thereby increase evaporation.
They circulate dry air throughout a structure: Many structures that have suffered a water intrusion contain more than one room or area that has been affected. The airmover can be used to circulate air from one affected area to the next. This eliminates the need for several smaller dehumidifiers spread throughout the structure and makes it possible to use fewer, larger, more efficient dehumidifiers.
Determining how many airmovers to place
Enough airmovers must be installed to create airflow across each and every affected surface. The number of airmovers necessary is dependent upon the number of wet surfaces, the amount of free water, and the ability for air to reach all wet materials.
Industry groups have agreed upon established numbers of airmovers needed initially in an average structure. These established numbers are based upon the materials being dried, and are best understood using "classes of water loss." Each class is briefly described below:
Class 1: Water intrusion involving wet plywood, concrete, structural wood, and other dense materials. Very little wet carpet and underlay are present.
Class 2: Water intrusion involving whole rooms of wet carpet and underlay, wet plaster board with sustained wicking of less than 600mm.
Class 3: Water intrusion has resulted in whole rooms of wet carpet and pad, wet plaster board with sustained wicking in excess of 600mm. Generally, water has come from overhead.
Class 4: Specialty drying situations where the affected materials contain deep pockets of saturation. The wet surface may be inaccessible to the standard airmover, water is typically bound and evaporation will be slow.
Once the class of water loss is defined, the amount of air movement necessary can be estimated:
In a Class 1 water loss, one airmover is needed for every 14-28m2. In a Class 2 or Class 3 water loss, one airmover is needed for every 4.5-5.5m2.
Regardless of class, an airmover is needed for every area, including closets and bay windows.
Several factors will influence their actual installation, such as the type of material affected, the degree of saturation, the accessibility of the actual wet surface and equipment availability. In a class two or three water loss, airmovers should be placed every 3-4 lineal metres along the wall. Airmovers should be directed toward the wall at a 10°-45° angle, depending upon the type of airmover. The snout of the airmover should be within 25 mm of the wall but not touching it. All airmovers in each area should be facing the same direction, whether clockwise or anti-clockwise, to ensure that airmovers are not "pushing" against each other.
Specialised airmovers are used for Class 4 water intrusions, as the affected material generally is dense, and will contain primarily bound moisture. When determining the air movement needed for a special situation, keep in mind the main effects of airflow: removing the boundary layer and distributing dry air in the structure. If airflow can achieve either of these objectives, it should be used.
Adequate air movement is critical to efficient and effective drying.
Follow these guidelines to ensure that you are taking full advantage of the evaporation benefits of airmovers to speed your drying. More articles from Dri-Eaz Products: | 
