Louvers play an important role when used in an industrial ventilation system. Their function is to allow air to pass through them while keeping out unwanted elements such as water, dirt, sand, and fine particles when fitted with filters. Selecting the right louver for an application requires knowing how to navigate through all options and then sizing it properly to provide the required air flow. In this week’s blog, I’ll share some of our tips for selecting the right louver.
Keeping Things Out
The first step in selecting a louver is determining what needs to be prevented from entering the building through the air stream. Water, dust, sand, debris, bugs and birds are all items that need to be kept out. Once you have determined what needs to be kept out, here are tips on what to expect for that style of louver:
Water
For water penetration prevention, it is important to select a drainable blade louver. This type of louver blade has a gutter designed to catch water that is separated from the air stream. The gutters lead to special channels in the louver’s jambs that drain the excess water down the sides of the louver and out the sill. The advantage of a drainable blade is that it provides more protection against water coming down the front of the louver and being sucked back in through the louver on lower blades.
Dust and Sand
Where there is a significant amount of dust and sand in the air, a sand louver should be used. Sand louver have specially designed blades that overlap to trap the dust or sand. The blades of a sand louver are installed vertically so that when dust or sand has been trapped, it falls down the length of the blade and out the bottom of the louver. Because of the geometry of the blade and their overlapping configuration, sand louvers have a significant pressure drop that must be considered in the fan selection.
Fine Particles
A sand louver can remove large particles. For fine particles, the louver will need to have a filter. The size of small particles that a filter can trap is determined by the MERV rating of the filter. The important thing to remember filters on supply air intakes is that they need to be changed when they become loaded with the fine particles. Adding a filter gauge to the filter box will is the best way to know when a filter needs to be changed.
Bugs and Birds
Preventing bugs and birds from entering through a louver is done by adding a screen on the back side. The best type of screen is made with woven wire. That is because the wire is round and will provide the lowest pressure drop.
Louver Attributes
The second step in selecting the right louver is to decide on the material, depth, and blade position of the louver:
Material
Most industrial louvers are made from either aluminum or galvanized steel although some extreme applications may require stainless steel. Aluminum has the advantage of being easier to form so aluminum louver blades tend to have better designs for water resistance. Louvers made of aluminum are also lighter and provide better corrosion resistance. Aluminum can be painted with any color or can come with an anodized finish. For all of these reasons, we prefer to use aluminum.
Depth
The common depths for industrial louvers are 4 and 6 inches. The main advantage of the 6” depth is that it has more free area which means a lower pressure drop at any velocity. Another advantage is that it has a higher water penetration velocity. Unless there is a restriction on louver depth, we prefer to use the deeper option.
Fixed or Adjustable Blades
Although louvers are mostly thought of to have fixed blades, there are options with adjustable blades. The advantage of an adjustable blade louver is that it can be completely closed to prevent water penetration during sever weather or to keep in heat during the winter. The downside to moveable blade louvers is that they cost more. Unless adjustable blades are specified by the customer, we prefer the fixed blade louvers.
Sizing
The final step in selecting the right louver is determining the size. The art of sizing a louver starts with determining the desired air velocity through the louver. A higher air velocity has a higher risk of water penetration which most often starts at 1,000 (we need to look at this) ft/min. A lower air velocity causes less resistance so there is a lower static pressure drop. We prefer to size louvers that have static pressure drops under 0.15 in. w.g. Keeping the air velocity through the louver in the range of 700 to 900 ft/min yields both a lower risk of water penetration and a lower pressure drop.
Once the air velocity is selected, divide the required air flow, in CFM, by the air velocity to determine the amount of free area, in sq. ft., that will be need in the louver. Now divide the amount of free area by the percentage of free area for the style of louver that has been selected. The result will be the total area of the louver that is need.
The next step in sizing a louver is to look at the dimensional chart provided by the manufacture to find a size based on height and width that comes closest to providing the total louver area that is needed. Based on the height and width limitations, the louver may need to be sized with two or more panels.
The final step is to determine if the louver will fit in the desired location. If not, the air velocity can be increased to decrease the total area of the louver but this will increase the pressure drop of the louver based on how much the area is reduced.
Conclusion
At Eldridge, our 77 years of experience has made us experts at designing and selecting the right louver for every application. To meet the needs of our marine customers, we designed the Eldridge ESL-6 Storm Louver for use in our patented Eldridge Storm Guard Hoods. The 6” version of the Eldridge ESL-6 Storm Louver can withstand rain falling at a rate of 14” per hour with a 50 MPH wind and prevent 99.9% of the water from penetrating.
Not every industrial louver application will require such extreme problem solving. However, our ventilation experts will work just as hard to make sure that you are selecting the right louver for your application.