With the wide selection of louvers available today, choosing the proper louver for your application may appear to be a difficult task. However, by considering the requirements of the application and understanding what models are available, louver selection can be made much easier. In this article, we will examine factors that affect louver selection and some of the more common louver styles available today.
Selection generally starts with a desired airflow and practically any louver style will handle any amount of airflow if it’s made large enough. However, system designers usually have to deal with size constraints. The task then becomes finding a louver will handle the desired volume while providing adequate rain resistance and airflow characteristics. Here are some considerations:
• Rain Resistance – Rain penetration through louvers is usually undesirable. However, in applications where the louvers are close to water sensitive surfaces or devices, it can be extremely harmful. Are there provisions in the building for managing rain that may penetrate the louver during storms, such as floor or plenum drains? If not, will rain infiltration during storms create significant problems for the building? If rain penetration will be managed or is not harmful, a standard louver may be suitable. If the application cannot accept rain penetration, wind driven rain resistant louvers should be utilized.
• Pressure Drop – How much pressure drop is acceptable? This may be the deciding factor in the louver selection. Most standard louvers are designed to provide good air performance within their intended airflow range. While the airflow capacity of wind driven rain resistant models are usually higher, the additional airflow may create more pressure drop than with standard louvers. Keep in mind that published AMCA certified pressure drop performance does not include the effect of a bird or insect screen. This can add from 5% to 15% pressure drop depending on the screen type.
Other louver selection considerations:
• Sound – Is the louver going supplying air to a noisy area such as a generator or pump room? If so, acoustical designs are available to reduce sound penetration through the louver.
• Security and/or Sight Restriction – Louver applications in areas subject to frequent human contact may benefit from sightproof louvers. Sightproof models restrict see-through and provide less opportunity for vandals to penetrate the louver wall.
• Airflow Shut-off – For applications that only require airflow at certain times, operable or combination louvers are available that completely close the opening. Good choices for emergency generator or warehouse applications.
• Appearance – Is there a particular louver design or appearance desired? Or, does the louver need to blend with or match other elements in the building? For architectural louver applications, appearance is sometimes the most important feature. The appearance of louvers can be changed to fit a variety of needs with visible or hidden mullions, blade orientation and spacing, and the type of finish applied.
• Structural Integrity – Windloads have a considerable effect on louver construction, especially with louvers that are tall or in hurricane-prone areas. High windloads may make the use of certain types of louvers impractical, particularly thinline models due to their lightweight design.
Now that we’ve looked at some of the considerations for louver selection, let’s review some of the common louver styles available today.
• Standard Louvers – These are the standard horizontal blade models that have been available for many years. Typically, they are 4” to 6” deep and are tested in the AMCA “still air” water penetration test. These models feature fairly wide blade spacing that can provide good free area and pressure drop performance. However, their wide blade spacing makes them far less effective at rain protection than wind driven rain resistant models. To give an idea of airflow capacity, a popular 4” deep standard louver with drainable blades can handle approximately 400 cfm per ft² of louver face in a 4’ square size, and generates roughly .15” pressure drop. Common Standard Louver styles:
o Non-drainable blade louvers – The louver blades do not collect water, therefore rain water cascades from blade to blade. Most often used in weather-protected areas and continuous blade applications.
o Drainable blade louvers – The louver blades feature small gutters in their profiles that collect water and drain them to downspouts in the jamb frames (fig. 1). Better rain resistance than non-drainable models, but not effective in storm conditions. Often utilizes visible vertical mullions to enclose the downspouts.
o Sightproof louvers – Most often utilizes a chevron or inverted “Y” shaped blade to prevent see-through. Also prevents objects from being passed through the louver wall. Free area and pressure drop performance usually worse than other standard louvers requiring larger louvers for the same airflow.
o Thinline louvers – Louvers that are 1” to 3” deep. Generally made for PTAC or curtain wall applications. Also a good choice for small openings but not for large sizes or high windload situations.
• Wind Driven Rain Resistant Louvers – This louver style has developed in the last decade and utilizes new technology to minimize rain penetration. The louver depths typically range from 4” to 8”. The blades may be positioned horizontally or vertically and generally feature complex profiles. Blade spacing is much closer than standard louvers, ranging from 1” to 3” center to center in most cases. Unlike Standard Louvers, these are tested in AMCA’s Wind Driven Rain Penetration Test which simulates storm conditions (fig. 2). Louvers are subjected to heavy rain and wind effects. Many models provide over 99% efficiency at preventing water penetration. Looking at a 4’ square size, a popular 6” deep vertical blade wind driven rain resistant design will handle 900 cfm per ft² of louver face and generate roughly .35” pressure drop. Some characteristics of these louvers:
o Horizontal Blade Models – Look much like Standard Louvers, but with closer blade spacing (fig. 3). Performs well in the low weather condition test (3”/hr rain & 29 mph wind). Some continuous blade models are available.
o Vertical Blade Models – Provides the best performance. Some are 100% effective in the high weather condition test (8”/hr rain & 50 mph wind).
o Cost – Can be as much as 2 to 3 times as much as Standard Louvers, but in many cases can be ½ the size. And they offer rain protection not available with Standard Louvers in any size.
• Acoustical Louvers – The louver blades are filled with sound-deadening material, typically mineral wool or fiberglass. They are usually fairly deep, as much as 12”. These models can provide 10 to 12 db noise reduction in the lower octave bands in a Free Field condition. Free area is usually very low compared to other louvers, so Acoustical Louvers must be made larger to handle comparable airflow. For comparison, a common 12” deep model handles 200 cfm per ft² of louver face in a 4’ square size and generates roughly .10” pressure drop. Acoustical louvers most often utilize visible mullion construction.
• Operable & Combination Louvers – These models feature operable blades that can be closed when airflow is not required. The airflow shut-off capability prevents rain and humidity from entering the room when the louver is closed. Combination louvers feature a set of stationary blades in front of the operable blades that produce a consistent exterior appearance at all times. Airflow capacity per ft² is similar to that of Standard Louvers.
The louver styles described above make up the majority of louvers available, but there other louver products available. Hurricane resistant louvers, penthouses and equipment screens are some of the other products available for more specialized applications. Even though there are many louver products to choose from, their selection can be made easier with a basic understanding of what styles are available and their applications. Whatever your application, there probably is a louver available that will meet the requirements.
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