Louver
From Swikipedia
Introduction
A louver is a window, blind or shutter with horizontal or, vertical slats, that are angled to admit light and air, but to keep out rain, direct sunshine, and noise. The angle of the slats may be adjustable, usual in blinds and windows, or fixed.
Brief Description
Some modern louver systems serve to improve indoor daylighting. Fixed mirrored louver systems can limit glare and of redirect diffuse light. Such louvers may be integrated in between two panes of double glazing.
Basic Considerations for selecting louvers:
1. Free Area:
Free area is derived by taking the total open area of a louver (after subtracting all obstructions - blades and frame) and dividing by the overall wall opening. This gives a comparison of a louvered opening to an unobstructed opening. Common louver free areas range from 35% to 60% of the wall opening (65% to 40% obstructed). A high percentage free area is beneficial because more air can enter into a smaller wall opening, reducing the cost of the wall opening and louver.
2. Water Penetration:
First Point of Water Penetration is the point at which a louver allows the passage of water through the louver. It is a threshold measurement of air intake velocity at which the louver will begin leaking (in feet per minute or fpm).
3. Resistance to Airflow:
Every obstruction in the air-stream creates resistance - louvers, ductwork, filters, coils, building structure, etc. The resistance of the louver can be measured by running air through the louver and measuring the pressure differential at various free area velocities (measured in water gauge or wg). Every louver will create resistance based on the frame and blade shapes. Lower blade angles or more aerodynamic shapes create less resistance. It is important to know the free area velocity through the louver in order to properly evaluate the overall resistance to airflow. For a majority of applications, one can calculate the pressure loss of the louver at the required free area velocity and determine if it is acceptable. The resistance created can be detrimental to the application of fans and other air movement equipment, so one should attempt to minimize it.
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