It's the available open area of a louver with removing the blades, frame, and stiffeners. AMCA publication 500-L prescribes the method for determining louver free area.

Note: Most often, the louver spec calls for 50% free area, but the size of the louver makes a big difference in the free area. For example, a 48” x 48” AMCA tested louver may have a 50% free area, but the same louver in a much smaller size may only have 30% free area and the opposite for larger assemblies could have more than 60% free area.

So, specifying a louver on its 48” x 48” free area size is not recommended.

Pressure drop is the difference in airflow resistance (pressure) from one side of a louver to another, typically measured by inches of water gauge at different free area velocities. Higher pressure drop requires more energy to move air through the louver. Therefore, a lower pressure drop is more desirable. There is not a direct correlation between high free area and low pressure drop.

AMCA is the Air Movement and Control Association International. The mission of AMCA International is to promote the health and growth of the industries covered by its scope and the members of the association consistent with the interests of the public. AMCA develops industry related test standards for air movement and control products while independently certifying product performance to ensure reliable and accurate product performance. For more information about AMCA please visit www.amca.org.

With respect to louver products, the AMCA Listing Program is reserved for the AMCA 540 debris impact test and the AMCA 550 High Velocity Wind Driven Rain test. Unlike the AMCA 500-L test procedures, AMCA 540 and AMCA 550 are “pass/fail” criteria test procedures. By displaying the AMCA Listing label AMCA is certifying that the louver product(s) in question have passed the AMCA 540 and/or AMCA 550 standard. The AMCA 540 and/or 550 standards are requirements for the Hurricane Prone Region as defined by the International Building Code.

AMCA 500-L is the publication that defines louver test procedures and how manufacturers portray performance for louver Air Performance, Water Penetration, Wind Driven Rain, Air Leakage, and Sound Performance.

The AMCA 500-L Water Penetration standard is a static water test for louver products. The test standard simulates rain falling straight down in front of a louver test specimen at a rate of 4 in./hr. A fan attempts to pull water through the louver from a fully enclosed chamber behind the louver. The free area velocity whereby 0.01 oz of water per square foot of louver free area is measurable in the chamber behind the louvers is the Beginning Point of Water Penetration. It is always advisable to size conventional intake application louver comfortably below the Beginning Point of Water Penetration.

The AMCA 500-L Wind Driven Rain standard is a dynamic water test for louver products and is not to be confused with AMCA 550 High Velocity Wind Driven Rain, which is a requirement of the Hurricane Prone Region. The AMCA 500-L Wind Driven Rain test simulates horizontal driving rain by positioning a wind-generating fan that simulates either a 29 MPH or 50 MPH external wind. Between the wind-generating fan and the louver test specimen, water spray nozzles drive either 3 or 8 in. rain/hr. at the louvers (29 MPH/3 in. rain/hr., 50 MPH/8 in. rain/hr.). A fan attempts to pull water through the louver from a fully enclosed chamber behind the louver. The louver is given a letter grade rating at specific escalating inlet velocities, which defines the percentage of water rejection (A = 99%, B = 95% - 98.9%, C = 80% - 94.9%, D = <80%).

AMCA 511 is the Certified Ratings Program. Relative to louver products, if the louver manufacturer has tested their product(s) in accordance with any or all of the AMCA 500-L test procedures the louver manufacturer may elect to have AMCA certify their performance in accordance with the AMCA 511 Certified Ratings Program and display the AMCA Seal on product literature or the product itself. Keep in mind the AMCA 500-L test procedures are not “pass/fail”. AMCA Certified means that AMCA concurs the product was tested appropriately and that AMCA endorses the displayed product performance.

AMCA 540 is the Test Method for Louvers Impacted by Wind Borne Debris. The International Building Code and the Florida Building Code dictates that louvers installed within 30 ft. of grade in the Wind-Borne Debris Region of the Hurricane-Prone Region need to comply with AMCA 540. The AMCA 540 standard subjects a louver to the impacts of a 9 lb. 2 x 4 traveling at either 34 MPH (Missile Level D) or 55 MPH (Missile Level E). While Missile Level D is required for most commercial construction, Missile Level E is required for all critical or enhanced facilities and should be specified as such. The louver must show that the 2 x 4 does not pass through the louver and that the louver components maintain connectivity. Complete cosmetic destruction is acceptable.

AMCA 550 is the Test Method for High Velocity Rain Resistant Louvers and is not to be confused with AMCA 500-L Wind Driven Rain. The International Mechanical Code and Florida Mechanical Code dictates that all intake and exhaust louvers located in the Hurricane Prone need to comply with AMCA 550. The AMCA 550 standard subjects a louver to 35, 70, 90 and 110 MPH external wind while spraying horizontal driving rain at a rate of 8.8 in./hr. The louver must show that no more than 1% of the total sprayed water volume is measurable in the water collection apparatus positioned in the test chamber behind the louver.

Stationary Louvers – are designed to allow air to pass through while blocking out debris and water in intake and exhaust applications.

Drainable Louvers - are commonly used in areas with heavy rainfall and are similar to stationary louvers, but they are designed to remove water that collects on the blades.

Wind-Driven Rain Louvers – are designed to keep out wind-driven rain. Special blade designs prevent rain from entering the building, even under high wind conditions.

Acoustical Louvers – are designed to reduce noise levels. They are commonly used in areas with high noise pollution, such as factories, generators, airports, or highway tunnels.

Combination Louvers – are designed to provide both intake and exhaust ventilation.

Hurricane Louvers - are designed to withstand high winds and heavy rainfall. They are commonly used in coastal areas prone to hurricanes.

Miami Dade Approved Louver - are designed with exceptional protection against wind-driven rain under severe conditions. Features: AMCA 540 and AMCA 550 Listed for wind-borne debris and high velocity rain. Large missile impact resistant per Miami-Dade TAS-201 test protocol.

Penthouses – are louvers that are designed to cover rooftop equipment. They are commonly used in commercial buildings to conceal HVAC systems.

FEMA Louver – are heavy duty steel louver/grilles designed to protect exterior wall openings against severe circumstances on FEMA 320 or 361 compliant safe rooms and storm shelters.

Equipment Screens – are roof or ground-mounted panels that create a visual barrier and conceal mechanical equipment from sight.

No, all test standards for louver performance do not include bird or insect screen. United Enertech has tested the effects of bird screen on our louvers, and depending upon the bird screen size and shape, the performance is different.