Louvers are designed to let air in while keeping other things out, like rain or snow. When picking a louver, you need to which of these two is more important.
AMCA Ratings can help you determine which louvers are best at a given task.
AMCA - A Quick Review
First, let's review. AMCA stands for the Air Movement and Control Association: an international, not-for-profit association of manufacturers who build air-system components, including fans, louvers, dampers, air-flow measurement devices, and other HVAC components.
AMCA establishes reliable standards and test protocols for HVAC equipment. When an air-flow product has been tested under these protocols, it receives an AMCA Rating Seal. Industry professionals look for these seals when selecting air-control products.
For this blog, we’ll go over the test required for a Wind Driven Rain seal.
The Test - A Tale of Two Test Assemblies
Wind Driven Rain testing involves two assemblies: one that mimics an air intake duct and another that mimics rainfall in windy conditions.
For the first assembly, a sample louver, measuring 1 meter wide by 1 meter high, is installed in a simulated opening. This is connected to ductwork that leads to a fan, which will draw air through the louver and into the duct. This first assembly simulates an intake duct during standard operation, as it does in the Water Penetration test.
The second assembly is comprised of a fan connected through ductwork to a series of water sprinklers on the other end. These sprinklers will face the sample louver and spray water directly at the louver face, while the fan drives the water forward. This second assembly will simulate wind-driven rain.
For the Wind Driven Rain test, each louver is tested at two simulated rainfall rates:
- 3 inches of rainfall per hour, at a wind velocity of 29 MPH
- 8 inches of rainfall per hour, at a wind velocity of 50 MPH.
The goal of Wind Driven Rain testing is to ensure that the louver will block heavy rain fall while allowing air flow through the louver.
The Results - Measuring Effectiveness
Data is collected at several points in each test as the Core Ventilation rises. Testers record Free Area Ventilation (the amount of air coming in through the louver), Free Area Velocity (the speed of the air), and an Effectiveness Ratio.
The Effectiveness Ratio is the percentage of total rainwater blocked by the louver during the test. With this ratio, the louver is assigned an Effectiveness Rating Class:
- Class A – 100 to 99% Effectiveness Rating
- Class B – 98.9% to 95% Effectiveness Rating
- Class C – 94.9% to 80% Effectiveness Rating
- Class D – 79.9% Effectiveness Rating or below
When both tests are complete, the test data is recorded in a table for each test point, including the Effectiveness Rating Class. This table allows you to gauge the louver’s effectiveness through the course of both tests. This will give you an accurate understanding of its capabilities in real-world situations.
Meeting Requirements - Wind Driven Rain & Severe Weather
If you’re deciding on a Wind Driven Rain louver, you likely have a requirement for how well the louver blocks severe weather.
You may need to ventilate a room with electrical equipment, such as computers or generators. Or severe weather events may be common in your area.
In these instances, your goal should be to keep your interior spaces dry. A standard louver may provide some protection from rain water, but they will likely fail at blocking serious weather conditons. Wind Driven Rain louvers are tested and rated to protect against severe weather. For these requirements, always looks for the Wind Driven Rain seal.
One More Thing - Hurricanes!
Wind Driven Rain louvers are tested to reject heavy rainfall at high wind speeds, but there may be instances where you need more protection. What if you’re building in a High Velocity Hurricane Zone (HVHZ)?
In a Category 1 Hurricane, wind speeds can be as low as 74 MPH or as high as 94 MPH. Those wind speeds are well above the maximum speed of the Wind Driven Rain test. And worse, that’s just the first category. In these cases, you would need a hurricane resistant louver.
A Hurricane Louver is designed to withstand hurricane-force wind, heavy rainfall, and impacts from windborne debris. These louvers are tested by Miami-Dade County and by AMCA. For Miami-Dade, each louver is certified for use in HVHZs. You can use this search tool to find Miami-Dade certified louvers and HVHZ approved products.
For AMCA, these louvers are rated under Standard 540, for Windborne Debris Impact Resistance, and Standard 550, for High Velocity Wind Driven Rain Resistance.
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Our louver course, An Introduction to Louvers, goes over all of the basic stats, terms, and principles involved in choosing louvers for any application.
This course provides continuing education credits for a variety of institutions, including AIA's LIUs. Learn the basics of louvers and earn credit, at your own pace. Visit the MCDLG course page on AECDaily.com today!