Important Considerations for Air Louvers
Air louvers are a component of ventilation systems where several fixed or movable blades are attached within a frame and can allow some directional flow of air through the system. At the same time, air louvers keep out unwanted debris such as water, dust and dirt. Some important considerations when choosing air louvers for your home or business application are free area, water penetration, and pressure loss. If you understand these concepts then you can choose the appropriate louver for your application.
Free area is basically the amount of open area that the air louvers have to offer inside their frames and between their blades. The free area is the unobstructed opening that the louvers offer when installed in the space. An example of this would be, most air louvers offer free areas from 35% to 60% of the actual wall opening they are mounted in. This means that 40% to 65% of the area is obstructed. The higher the percentage of free area the better since more air flow can enter into a smaller opening. In the long run this reduces the cost of the construction/installation and the air louver production.
Water Penetration is the point at which the air louvers allow the seepage of water through the louver. It's a measurement of air intake the determines at what point the air louvers will begin leaking. This is done usually in feet per minute (or fpm). With traditional air louvers the regular method of testing for water penetration is to take a pre-measured amount of water and pour it in front of the air louvers while there is an intake flow of air through the slats. The velocity of the airflow is increased until the water actually starts to enter through the air louvers. The results of this test are what are known as "the first point" of water penetration. A range on these test results would be 300 fpm (very poor resistance) to 1250 fpm (very good resistance).
Resistance to Airflow (Pressure Loss)
Any obstruction in the airflow creates resistance and loss of pressure. The resistance of the air louvers can be done by measuring airflow through the air louvers and recording the difference in pressures at different velocities. All air louvers will create at least some resistance because of their framing and blade shapes.
When the air louvers are adjusted so that there is lower blade angles or when the slats of the air louvers are of more aerodynamically shaped it creates less resistance. To test for the pressure loss you must know what the free area airflow velocity is through the air louvers. This allows proper evaluation of the overall resistance to airflow. For most applications, calculating the overall pressure loss of the air louvers at the necessary free area velocity will determine whether it's acceptable or not. The amount of resistance that is created by the slats can put extra stress on to fan motors and other components, so it's important to keep the resistance to a minimum.