Application of AMCA 550-Rated Wind-Driven-Rain-Resistant Louvers

Code Requirements

To meet the requirements of the International Building Code (IBC) and/or local building codes, louvers installed within a hurricane-prone region—defined in the 2021 IBC (Chapter 2) as well as Florida Building Code, Building, Seventh Edition (2020) (Chapter 2) as: (1) the U.S. Atlantic Ocean or Gulf of Mexico coast where the ultimate design wind speed for Risk Category II buildings (buildings and other structures except those that represent a low hazard to human life in the event of failure, those that represent a substantial hazard to human life in the event of failure, and those designated as essential facilities) is greater than 115 mph (51.4 m/s) or (2) Hawaii, Puerto Rico, Guam, the Virgin Islands, or American Samoa—must meet the requirements of ANSI/AMCA Standard 540, Test Method for Louvers Impacted by Wind Borne Debris.

To meet the requirements of the 2021 International Mechanical Code, intake and exhaust louvers installed within a hurricane-prone region must meet the requirements of ANSI/AMCA Standard 550.

The AMCA 550 Test

In an ANSI/AMCA Standard 550 test, a fan positioned in front of a louver specimen simulates wind speeds of 35, 70, 90, and 110 mph (15.6, 31.3, 40.2, and 49.2 m/s), while water nozzles positioned between the fan and the louver specimen simulate 8.8-in.- (223.5-mm-) per-hour horizontal driving rain. Each test is performed for 15 min, with the exception of the 110-mph (49.2-m/s) test, which is performed for 5 min. For a louver to pass an ANSI/AMCA Standard 550 test, no more than 1 percent of the total water sprayed may have penetrated the louver.

In the description of the louver test specimen in an ANSI/AMCA Standard 550 test report, the position of the blades—open or closed—will be noted, with the louver receiving a “pass – fully open,” “pass – fully closed,” or “fail” determination.

ANSI/AMCA Standard 550 allows three types of test specimens:

• Stationary-blade louver.
• Stationary-blade louver with rear-mounted control damper.
• Operable- (or combination-) blade louver.

Louver Test Specimens

Engineered to capture and reject rain at an acceptable rate without the need to stop the flow of air into a building, stationary-blade louvers most commonly are applied for intake and exhaust outside-air openings in critical or essential facilities where louvers are required to be open for life-safety purposes, such as providing a breathable atmosphere (as outlined in Chapter 16 of the Florida Building Code). Critical or essential facilities include hospitals, fire stations, police stations, and buildings where critical records are stored, the construction requirements of which are outlined in model and local codes. Increasingly, ANSI/AMCA Standard 550-rated louvers are being specified for critical-application facilities outside of high-velocity-hurricane-zone regions.

Stationary-blade louvers typically are horizontal-blade louvers (Photo A), vertical-blade louvers (Photo B), or “dual-module”/“dual-bladed” hybrid louvers with a set of horizontal blades in the front and a set of vertical blades in the rear (Photo C).

With gravity working in their favor, vertical-blade louvers usually outperform their horizontal-blade counterparts. To date, no purely horizontal-blade louver has been rated ANSI/AMCA Standard 550-compliant. Nevertheless, many architects and building owners prefer the look of horizontal-blade louvers. Where building aesthetics are concerned, a horizontal-blade appearance and ANSI/AMCA Standard 550-compliance can be achieved with a dual-module/dual-bladed hybrid louver or by mounting an operable control damper to the rear of a stationary horizontal-blade louver (Photo C).

Vertical-blade louvers come in a variety of frame depths, typically offer the smallest footprint, and are lighter and have a lower pressure drop than dual-module/dual-bladed hybrid louvers.

To pass the ANSI/AMCA Standard 550 test and be considered ANSI/AMCA Standard 550-compliant in the field, an operable control damper can be factory-mounted to the rear of a stationary horizontal-blade louver or an operable (or combination) horizontal-blade louver (Photo D) and kept in the closed position during a storm event, meaning airflow is shut off. During testing, a lever arm, manual hand quadrant, or turnbuckle, none of which is considered part of the test specimen or affects the rating determination of the louver, can be used to keep blades in the open or closed position. In the field, factory-mounted electric actuators (typically, two-position, fail-closed) controlled by a signal from the building or a device most commonly are required.

ANSI/AMCA Standard 550 High-Velocity-Rain-Resistant Louvers. Photo credit Nailor Industries Inc.

Additional Code Requirements

Louvers installed within a hurricane-prone region must be designed to withstand the wind loads and design pressures defined in the model codes and as detailed in ASCE/SEI 7-10, Minimum Design Loads for Buildings and Other Structures. Hurricane louvers typically have a maximum wind-load rating in pounds per square foot that may be size- and configuration-dependent. To withstand the rigorous testing and meet the requirements, large support brackets generally are required for proper installation. The most stringent of the requirements can be found in Miami-Dade and Broward counties, Florida, where Miami-Dade Notice of Acceptance- (NOA-) approved louvers typically are installed.

The requirement to control operable blades adds cost and complexity to a project design. There are practical limitations to the size of a single-section operable-blade louver or control damper. With these limitations and the need for additional support bracketry, it is not uncommon to see jackshaft-driven dampers on the rear of louvers, which adds significant material (actuators, wiring, relays, transformers, etc.) and installation-labor (heavier assemblies requiring teams, lifts, or cranes; additional field wiring) costs.

For louvers required to have blades in the closed position during a storm event, it is important to consider the operation of the building and the control sequence of the air-moving systems. Operating the air-moving systems and creating a negatively pressurized building will pull in unconditioned outside air through all openings in the structure. Meanwhile, the water-rejection capabilities of the louvers may be negatively affected.

Conclusion

Regardless of application, intake and exhaust louvers should be tested in accordance with ANSI/AMCA Standard 500-L, Laboratory Methods of Testing Louvers for Rating, and certified to AMCA Publication 511, Certified Ratings Program Product Rating Manual for Air Control Devices. Standard certifications for AMCA Publication 511 include air performance, water penetration, and wind-driven rain.

Hurricane louvers that pass ANSI/AMCA Standard 540 and/or ANSI/AMCA Standard 550 testing can be listed under AMCA Publication 512, AMCA Listing Label Program. Unlike regional programs such as the Florida Building Code, Miami-Dade, and the Texas Department of Insurance, AMCA Publication 512 provides performance check-testing of certified products.

About the Author

Michael J. Bulzomi is product manager, commercial dampers, for Greenheck and formerly chair of the AMCA Louver Marketing Subcommittee.