Why wind driven rain? You may see that an upcoming project requires wind driven rain louvers at key points along the building’s envelope. Why? What is the difference between a wind driven rain louver and a standard louver? All louvers are supposed to protect against rainfall, right? What makes the wind driven rain louver better? The differences are important to understand. We will start by looking at the two main differences, testing and design.
Tougher Testing
First, wind driven rain louvers are tested under more intense conditions. Standard weather louvers undergo water penetration testing in accordance with AMCA Standard 500-L.
Water Penetration testing:
- In this test, water slides over the ventilation point as an intake fan draws air through the louver. This simulates water rejection in still air conditions, where the only air movement comes from the system intake.
- Technicians increase the intake air speed and measure the water that passes through the louver. The test ends when the amount of water infiltration reaches 0.01 ounces per square foot, or when the intake air speed exceeds 1250 feet per minute.
- This stopping point becomes the louver’s beginning point of water penetration, which designers use to determine the louver’s effectiveness.
- If the intake speed exceeds 1250 feet per minute, with less than 0.01 ounces of water infiltration, then the beginning point of water penetration is “greater than 1250 FPM”.
Wind Driven Rain testing:
- In this test, a fan blows air through a chamber of water sprayer and onto the louver’s face while an intake fan draws air through the louver. This simulates gusts of wind during a storm.
- Technicians will increase the simulated wind speed and measure the amount of water that passes into the chamber beyond the louver. They assign an effectiveness rating for each increase in wind speed, depending on the amount of water rejected by the louver.
- Effectiveness Class A means the louver rejected at least 99% of incoming rain.
- The louver receives a Class D rating if it can’t reject more than 80% of incoming rain.
- The wind driven rain test is repeated at a higher simulated wind speed and with more rain. Technicians measure the water collected in the chamber as wind speed increases and assign an effectiveness rating.
- Effectiveness ratings provide a better understanding of how the louver will perform in different weather conditions.
Wind driven rain testing requires more from the louver. It must block incoming rain before it can pass through the free area and quickly drain it out before it collects on the louver’s blades. Louvers can be tested under both standards, but not all louvers can complete the wind driven rain test.
Wind driven rain testing provides a more accurate picture of how the louver will perform in a weather event. The louver must be designed for severe weather to complete the test.
Designed for Water Rejection
Wind driven rain louvers are designed with features that catch water traveling in the air stream. You may notice little “hooks” along the blade profile, when viewing the louver’s drawings. These hooks catch the water in their curves, preventing it from passing through the louver. When the wind dies down, the captured water will slide down the blade towards drain channels along the blade.
These blade channels are connected to channels in the jambs, which lead to the sill of the louver. The sill will typically slope down towards the face of the louver, so that collected water slides out. These features aid in rejecting the captured water. Drain channels provide an avenue for water to leave the louver, so that it doesn’t collect on the blade and flood into the louver.
Drainable louvers will have drain channels, but they typically won’t have the catches that capture water. These two features, together, provide the best protection against wind driven rain.
Three Reasons to Choose Wind Driven Rain
As you can see, wind driven rain louvers are designed to protect. They are also tested under more rigorous standards. Are they always the best option? A wind driven rain louver may be the better option. Below are three reasons why you should choose a wind driven rain louver over a standard louver.
Reason 1: Better Protection, Same Size
Wind driven rain louvers are similar in size to standard louvers. Louver dimensions vary based on the size of the ventilation point, but their depth can differ from model to model. The average louver will have a four-inch frame depth. Smaller louvers can have a two-inch depth or less, depending on their design. Larger louvers will have a six- or eight-inch depth. Wind driven rain louvers provide advanced protection with similar frame depths.
For example, the LE-44 is a wind driven rain louver from AWV with a frame depth of four inches. This louver has been tested and bears the AMCA Ratings Seal for Water Penetration and Wind Driven Rain. Check the louver’s submittal for details on how it performed during these tests. The LE-44 provides enhanced protection from rainfall with a standard frame depth. Simply put, you don’t need a big, bulky louver to protect your system from heavy rain. Use a wind driven rain louver.
Reason 2: Minimal Impact on Airflow
Louver design is a balancing act between protection and performance. The louver must protect the system from water infiltration, but the blade features can hinder airflow. Airflow is important, especially when designing a system for efficiency. Wind driven rain louvers can strike this balance with a unique blade design, the chevron.
Chevron blades have a curved shape, instead of the standard flat profile. Air flows up one side of the blade and over the peak. Water on air stream will have a tough time moving up the incline of the blade, often falling down the blade. A catch can be placed at the peak of the blade, so that it captures any water that makes it over the incline. When the airflow subsides, the water rolls down the incline and into drain channels at the face of the blade. Airflow is less restricted with chevron blades, providing more efficient flow without sacrificing the necessary protection. Strike the right balance with chevron blades.
Reason 3: Be Prepared for Severe Weather
Severe weather is becoming increasingly common across the country. Your project may not have requirements for severe weather louvers, but the threat is still present during storm season. Standard louvers might work for your project, but you won't be able to easily switch them out when a major storm approaches. Wind driven rain louvers provide the best level of protection. A light shower can quickly turn into a full-blown storm in a matter of minutes. Keep your building and its occupants safe. Choose wind driven rain louvers from the outset and protect your HVAC systems from severe weather.
Wind Driven Rain Louvers from AWV
Consider louvers from AWV for your next project. We build every louver to order, so that everything fits the application. We mentioned the LE-44 above, but we offer wind driven rain louvers to meet your project’s needs. Browse our full offering online. Protect your openings from severe weather with AWV.
Ready to get started? Contact us today. We can help you find the best solution.
