![]() To prohibit sight through between blades, the shallow slope will also require narrow blade spacing (more blades for the same height). In general, shallow slope blades allow for higher free areas based on simple trigonometry. While free area is not the only consideration in selecting which louver to use, it can have a dramatic impact on performance. For unfiltered air, use the same precautions as Air Intake.Įvery louver model has a different blade and blade spacing, so the free area will vary based on the characteristics inherent in that design. If small mesh screens are desired, a regular cleaning of the screens should be scheduled (twice a year). Air Exhaust (fan forced): If the air has been filtered, any screen can be used.If any small mesh screen (1/2", 1/4", or insect screen) is desired for this application, a regular cleaning of the screen is required (once a month is recommended). Large opening bird screen (3/4") is the best choice. Air Intake (fan forced): Since the air in not yet filtered, the potential for accumulation of dirt and grime is high.Air Ventilation only: any screen selection is acceptable.If access to the screens is limited or maintenance is questionable, large mesh screen should be used. If left without maintenance, the screens will eventually block most of the airflow. But screens under airflow will eventually get embedded with dirt and grime, so most of the industry data is not relevant to real world application.įor small mesh screens (under 1/2" mesh) used at air intake locations, the buildup of dirt and grime can reduce the free area 10% to 90%. These tests demonstrated a slightly positive or negative effect on airflow through the louver (depending on the type of screen). AMCA (Air Movement and Control Association) tested and published results for the effect of screens on louver airflow and water penetration in their January 1994 Techspecs document. In general, the free area of a louver is unaffected by a clean screen. Dirty screens will eventually reduce the free area significantly. A very limited amount of industry testing has been done and the data is only relevant for new, clean screens. Many assumptions are made regarding rear screens on louvers. 8/12 pitch), the "DEAD" portion of the blade increases, reducing the overall free area of the louver. 35 degree blade slope) or the pitch of the triangle decreases (3/12 pitch vs. As the slope of the blade increases (45 degree blade slope vs. ![]() The angle slope of the blade and the pitch of the triangle will determine the free area reduction. We have selected a comparison between a rectangular and triangular louver to demonstrate this reduction.īecause the blade is sloped from front to rear AND it is being mitered to fit flush to an adjoining frame, some of the free area is eliminated (the rear edge of each blade is shorter than the front edge). A slope or curvature eliminates some functional portion of each blade at the connection to frames, thereby reducing the free area. The shape of the louver will have an effect on the free area percentage. Keep in mind that we still need to subtract the blade obstruction from these numbers. For example, the frame of the louver will take up more of the free area (as a percentage) as the louver size reduces (see Figure 1.1 below).Įven with a thin frame style (3/4" on all Architectural Louvers models) the percentage free area is significantly reduced on smaller size louvers. Most people think of percentage free area as a constant, regardless of size. Size plays the most significant role in free area variation. Each of these has an impact on the free area and should be considered when selecting louvers for your application.Īdditional information on the impact of free area on louver selection, please visit the linked page how louvers Never assume that sizes other than this will have the same percentage free area.įree area varies widely by size, options ( special shapes and screens), and louver model. The typical size for louver comparison is 48" Wide x 48" High - which is an industry standard. By subtracting any obstructions to airflow (frames and blades) from the overall opening size we get a net result - free area. ![]() Every louver, no matter what size, has a calculated free area.
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