Louver design guidelines for non-traditional areas

Today's wind-driven rain, hurricane, and noise control louvers offer practical solutions for demanding building conditions.

10/01/2009


    Traditional louvers in building designs include a common horizontal blade mounted in the intake or exhaust path on the envelope of the building. This approach has been used for decades with varying degrees of success. While traditional louvers can provide good free area and pressure drop characteristics, they can fall short of providing acceptable performance in severe or non-traditional applications. Today's wind-driven rain, hurricane, and acoustical louvers all provide solutions. These louvers can achieve desired objectives through frame, blade, and installation modifications and still maintain good airflow characteristics.

     

    WIND-DRIVEN RAIN LOUVERS

    Traditional horizontal blade louvers are designed and tested for water penetration in non-storm (“still air”) conditions (i.e., when the water or rain falls vertically in front of the louver). When subjected to wind-driven rain conditions where the water or rain approaches the louver at an angle or even horizontally, they offer little rain protection. Most storms, in any part of the world, fall into the latter category.

     

    To provide better rain protection for this application, manufacturers have developed unique extrusions for blade construction that actually prevent water infiltration in even the most severe storm conditions. These louvers have a closer blade spacing and more complex blade profiles than their traditional counterparts. They usually incorporate hooks and drains to collect water from the airstream before it can enter the building.

     

    To validate the wind-driven rain water penetration effectiveness of louvers, the Air Movement and Control Assn. International, Inc. (AMCA) developed test setup 5.11 (see Figure 1) and redefined the louver Certified Ratings Program (CRP) to capture this extraordinary performance.

     

    This stringent test subjects louvers to exterior wind and simulated rain injected into the airstream. This is a significantly more severe test than the original “still air” test setup 5.6 (see Figure 2) that uses system airflow only (no wind) and simulates rain that originates out of the airstream.

     

    Louvers are categorized from Class A to Class D on their ability to reject water (see Figure 3). Class A performance is the highest classification possible and signifies 99% or better rain rejection. In many cases, these louvers have been tested for 100% effectiveness indicating that no water from the “outside” passed though the louver to the “inside” in the test environment.

     

    Test 5.11 is performed at two rain and wind levels: first at 3 in. rain/hr @ 29 mph wind conditions, and second at 8 in. rain/hr @ 50 mph wind conditions.

     

    To give you an idea of the amount of rain involved, in the first condition (3 in. rain/hr @ 29 mph), 21 gallons of water are applied to the louver in one hour. To certify Class A performance, the louver must not allow more than 27 fluid ounces of water penetration.

     

    For comparison's sake, Table 1 shows the results when a traditional 6-in. deep drainable louver that meets the maximum performance as tested in “still air” 5.6 was subjected to 5.11 conditions. This “high-performance” louver's effectiveness was Class D @ 67%. In terms of water amount, that is nearly 7 gallons when subjected to the lower wind-driven criteria of 3 in. rain/hr @ 29 mph.

     

    Note that while the AMCA wind-driven rain test is an excellent simulation of “real world” conditions, it does not represent every possible weather and installation scenario. Louvers that provide 100% rain rejection in the test environment may allow some water penetration in certain field applications. These applications usually involve unusual external wind patterns or internal system airflow characteristics. Based on results from these AMCA tests, wind-driven rain louvers clearly outperform traditional louvers in these unique circumstances.

     

    Wind-driven rain testing also allows for higher velocities through the louver. Due to the added rain protection, more airflow can be achieved through the same size louver, or if using the same airflow, the size of the louver opening can be drastically reduced.

     

    The first wind-driven rain louvers were limited to a handful of horizontal and vertical blade models with relatively large frame depths and little mullion appearance flexibility. Louver manufacturers now offer a wide variety of blade styles, with frame depths ranging from 2 to 8 in., with hidden mullions for continuous blade construction. Vertical blade models generally provide the best overall performance because water does not pool on the blade surface. If, however, vertical blade models don't conform with the building's aesthetics, horizontal blade models are a suitable alternative.

     

    Due to the closer blade spacing, the cost per square foot of louver is higher for wind-driven rain models; however, reduced sizing as well as the assurance that water problems are resolved can reconcile these costs.

     

    HURRICANE LOUVERS

    Hurricanes and other severe weather events create some of the most demanding conditions that a building must endure. Missile impacts from flying debris can puncture the building envelope, allowing wind and rain to penetrate the structure. These forces can produce catastrophic damage to a building. For envelope protection, the building codes in Florida and much of the southeast United States now require elements such as louvers, glass, and walls to be constructed to more rigorous test standards. Hurricane louvers are structurally enhanced to survive in high wind loads, high pressures, and missile impacts. A fourth test, the hurricane rain test, incorporates very high-velocity wind and heavy rain effects.

     

    In Florida, all louvers installed as part of a building envelope generally must have a Florida Product Approval number; if they are used in Broward and Dade counties, they also must be Miami-Dade Approved. The product approvals validate that the products were successfully tested to the appropriate test protocols, and that the manufacturer is producing the products per the tested configurations. The installation method used for the product is also part of the product approval, and installing contractors must adhere to the manufacturer's approved installation instructions. Building inspectors then review the installations to verify compliance.

     

    Hurricane louvers provide one or more of the following:

     

    • High-velocity wind resistance

    • High-pressure differentials

    • Large-missile impact resistance

    • Wind-driven rain resistance

    In hurricane zones where the area behind the louver can handle rain penetration and wind pressure, louvers alone are tested to withstand the pressure and wind. There is no need for additional dampers. In applications where the room behind the louver is not designed for the pressure generated by high-velocity wind infiltration, louvers with integral operable blades or stationary louvers with dampers are required so they can be closed to protect the structure in the event of a hurricane.

     

    Many times, the areas behind the louver cannot manage rain infiltration. In these applications, in Florida specifically, the louver/damper assemblies must pass the strenuous Miami-Dade TAS-100(A), Wind-Driven Rain Resistance test before they can be installed. In many cases, louvers that meet these tests also will be AMCA-certified for air and water penetration performance, as well as for wind-driven rain performance.

     

    The Atlantic seaboard and the Gulf regions require these louvers by code (the ICC stands as the national code, but the impact-resistant requirement is regional to the coastal areas). However, they are ideal in any location where elevated envelope protection is desired. Specifiers for structures such as data centers and high-security facilities often select these products for added defense against weather or vandal damage. With a wide variety of blade styles and installation methods available, hurricane louvers are an excellent choice for many applications.

     

    ACOUSTICAL LOUVERS

    Acoustical louvers not only provide water penetration protection, but also offer a noise-attenuating solution for building owners. These louvers incorporate sound-deadening material installed on the underside of the blades to absorb noise that would otherwise radiate from the opening. Louver sound performance is determined through testing to the ASTM E 90 Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements . Performance is given in decibels of Free Field Noise Reduction (see Figure 4), which indicates noise reduction through the louver when measured in an open area (no reverberant room). AMCA includes sound performance in the CRP program per testing to the ASTM standard.

     

    Acoustical louvers constructed of formed steel or aluminum components are available with frame depths ranging from 4 to 12 in. Because the sound performance improves with more sound material, the deeper models generally provide the best noise reduction. However, the characteristics that make these louvers good at reducing noise also reduce their free area. Acoustical louvers generally provide slightly over half the free area of traditional “still air” wall louvers. This means that acoustical louvers usually need to be larger than standard louvers to handle the same amount of airflow. The initial cost of acoustical louvers, which is slightly higher than traditional louvers, will be insignificant when compared to the remedial costs of a noisy application after the building is completed.

     

    Architecturally, formed steel acoustical louvers have vertical visible mullions at 4 to 5 ft on center. As a rule, they do not use hidden blade supports, so the frame depth is generally the overall louver depth. Tall assemblies made of multiple stacked sections require additional supports for structural integrity. Extruded aluminum acoustical louvers look more like traditional wall louvers and therefore have a preferred aesthetic quality. The extruded blades feature sound-absorbing material on the rear and incorporate traditional louver blade spacing. The sound-absorbing material is thinner and therefore noise reduction capability is lower. But again, with the use of hidden mullions, a continuous blade appearance is possible, which is not the case with formed acoustical louvers. Table 2 compares the performance between typical formed and extruded aluminum acoustical louvers.

     

    Typical applications for acoustical louvers include schools, hospitals, performing arts centers, emergency-generator buildings, fresh- or waste-water pump buildings, mechanical rooms in commercial and industrial buildings that are near residential areas, and all types of factories; acoustical louvers can even be used as equipment screens.

     

    PERFORMANCE ASSURANCE

    In the battle against the elements—wind, rain, and noise—louvers can and do come out on top, all while enhancing the building's architecture. And with AMCA's Certified Ratings Program , specifiers get assurance that product performance has been tested and verified. Whether increased rain protection, severe wind resistance, impact resistance, or noise reduction is required, there are louvers tailor-made to provide superior performance.

     

    AMCA 5.11 Effectiveness Classes

     

    Figure 3: Louvers are categorized from Class A to Class D on their ability to reject water.

    Class A

    99% to 100%

    Class B

    95% to 98.9%

    Class C

    80% to 94.9%

    Class D

    Below 80%

     

     

    Frequency (Hz)

    63

    125

    250

    500

    1k

    2k

    4k

    8K

    stc

    Figure 4: A typical noise spectrum. Louver sound performance is determined through testing to the ASTM E 90 Standard, and is given in decibels of Free Field Noise Reduction (NR), which indicates noise reduction through the louver when measured in an open area (no reverberant room).

    Transmission loss

    10

    8

    9

    13

    17

    17

    13

    13

    15

    Noise reduction

    16

    14

    15

    19

    23

    23

    19

    19

    15

     

     

    Louver style

    Free area/sq ft (48x48 in.)

    Max. free area velocity fpm

    Volume cfm

    Wind-driven rain penetration gph*

    AMCA wind-driven rain rejection % and class

    *3 in. rain/hr @ 29 mph wind conditions.
    Table 1: A performance comparison of the two types of louvers subjected to 5.11 conditions. Under the less stringent 5.6 testing, the 6-in. traditional drainable louver is considered high-performance; under 5.11 it is rated at 67%, Class D.

    6-in. vertical blade wind-driven rain resistant

    6.8

    2,100

    14,400

    0

    100%, Class A

    6-in. traditional drainable

    9.0

    1,000

    9,000

    6.93

    67%, Class D

     

     

    Acoustical louver style

    Free area/sq ft (48x48 in.)

    Max. free area velocity fpm

    Volume cfm

    Free field noise reduction at 125 Hz

    Free field noise reduction at 8,000 Hz

    Table 2: A performance comparison of typical formed steel acoustical louvers versus extruded aluminum acoustical louvers.

    4-in. formed steel model

    4.75

    703

    3,340

    11

    16

    12-in. formed steel model

    3.70

    1,126

    4,166

    13

    24

    6-in. extruded aluminum model

    4.85

    1,019

    4,942

    7

    19

     

     

    Author Information

    JAMES LIVINGSTON is louver product marketing manager at Ruskin Co.

     



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