Louvers are an important part of a building’s HVAC system, allowing air to enter or exit the building while keeping out unwanted elements like rain, birds or insects. Louvers also act as an architectural component of the façade incorporating the building’s colors and design features. For applications located within the hurricane-prone region (HPR), louvers must also comply with specific requirements listed in the International Building Code (IBC). Construction professionals should take care to specify and procure the correct louver for their application, especially if in the hurricane-prone region.
Figure 2—AMCA 550 Test Chamber
How Does a Louver Work?
When ventilation occurs through a wall, a louver is mounted in the wall opening acting as the HVAC system’s first line of defense. The louver blades perform the heavy lifting, channeling water to the jambs by using engineered gutters within the blade. The most basic and lowest performing louver is a drainable louver that incorporates a single drain channel within the blade. The highest performing louver is a wind-driven rain louver, which features multiple channels and hooks, designed to resist captured rain from blowing through the louver during storms. Some wind-driven rain louvers have their blades mounted vertically, offering superior performance over typical horizontal blade louvers.
On louver submittals, manufacturers list dimensional, structural, airflow and rain-resistance performance data to aid in solving application questions. Most manufacturers elect to certify the performance ratings of their products through the Air Movement and Control Association (AMCA), a nonprofit international association of the world’s manufacturers of louvers and other air movement and control equipment. This ensures all ratings are developed in accordance with the stringent test standards set forth by AMCA.
Louver Testing
AMCA 500-L is considered the gold standard for evaluating a louver’s air and water performance. This test is comprised of three parts: air performance, water penetration and wind-driven rain. The air performance portion measures the resistanceto airflow of the louver as static pressure drop. Ahigher louver static pressure drop results in higher energy operating costs, since the HVAC system will need to overcome the resistance.
The water penetration portion provides a good comparison of what airflow the louver can operate under without bringing in water during a non-wind-driven rain event. This is measured as the beginning point of water penetration and is measured in feet per minute, or cubic feet per minute of airflow. A higher rating means the louver has less chance of letting rain through during operation.
Finally, the wind-driven rain portion is the most realistic tool to use when comparing louver rain performance. The wind-driven rain test simulates rainfall from 3 to 8.8 inches of rain per hour, along with wind speeds of 29 to 50 miles per hour. While subjected to the wind-driven rain, airflow is drawn through the louver and the water penetration effectiveness is measured in terms of percent water rejected. For example, a 99% score means that 99% of the water was rejected, which is considered a Class A louver.
AMCA 500-L Wind-Driven Rain Penetration Classes
Class: Effectiveness (water rejected)
A: 100% – 99%
B: 98.9% to 95%
C: 94.9% to 80%
D: Below 80%
Figure 1
Hurricane-Prone Region Requirements
The IBC defines the HPR as any location along the U.S. Atlantic or Gulf of Mexico coasts where the basic wind speed for a Risk Category II building is greater than 115 miles per hour. Additionally, Hawaii, Puerto Rico, Guam, the US Virgin Islands and American Samoa are also considered part of the HPR. Effectively 17 US states are either partly or completely within the HPR (Figure1).
The IBC states that all air intake and exhaust louvers applied within the HPR must comply with the AMCA 550 High Velocity Wind-Driven Rain standard. The AMCA 550 test standard is one of the most stringent tests a louver can undergo, which is why only a select few pass this test. Louvers are subjected to simulated rainfall of 8.8 inches of rain per hour, along with winds of up to 110 mph for a period of 50 minutes. The louver passes the test if no more than 1% of the total sprayed water volume makes it through the louver. (Figure2)
Historically, vertical blade louvers were the only designs that pass this test, as horizontal blade louvers failed to evacuate water from the airstream. Eventually, dual-module louvers evolved to incorporate a vertical blade louver behind a horizontal blade louver. These dual-module units are often deeper and more costly than vertical blade-only units, but benefit by having the familiar look of horizontal blades.
What to Specify
Ultimately, the louver you choose will have to be a balance of first cost, operating cost, appearance, code compliance and rain performance. If located within an area that experiences wind-driven rain, its best to specify a louver that can maintain a Class A wind-driven rain rating at your desired airflow. If located within the Hurricane Prone Region, you must specify an AMCA 550 listed louver. If you want the highest performing louver available that also has a relatively low cost, look no further than vertical blade, storm-class louvers.
Greg Ewan is the segment manager at Airolite Co. LLC, a Schofield, Wis.-based manufacturer of louvers, sun controls and grilles. To learn more, visit www.airolite.com.