Selecting a performance louvre is often a compromise between airflow efficiency and rain defence. It is therefore important to know the answers to a few key questions before you start your selection, so that you can be sure to choose the right system. Specifying the wrong louvre system could cause problems internally, to plant and machinery or surfaces behind the louvre either by allowing rain water penetration or from restricting airflow. So let’s get started…
1. Do you know the required airflow through the Louvre?
When selecting ‘weather louvres’ one of the most important aspects is the design air intake velocity or face velocity. The higher the face velocity the more difficult it is to prevent water penetration. During the testing of weather louvres to BS EN 13130 they are subjected to a range (0.0m/s to 3.5m/s) of face velocities to determine their rain defence performance.
Tip: Always ensure you know the performance of the louvre at YOUR air intake face velocity before specifying.
2. How efficient is your louvre?
The airflow efficiency of a louvre is simply how freely it allows air to pass through it, with the overall ‘aerodynamic free area’ determined by the aerodynamic coefficient (Cd) and face area of the louvre panel. The greater the resistance to air moving through the louvre, the greater the difference in pressure between outside and inside of the louvre, known as the pressure drop.
Where ‘energy consumption’ is important, the lower the pressure drop, the less fan power will be required. Increasing the size of the louvre at the design stage means that the required volume air flow rate can be achieved, but at a lower face velocity and reduced fan power.
3. What amount of water penetration is acceptable for your project?
As well as allowing air to flow through it, weather (rain defence) louvres must also keep wind driven rain out. Acceptable levels of water penetration are dependent upon the application and how important it is for the area beyond the louvre to stay dry. We find the best way to narrow down your louvre selection is to look at the BS EN 13030:2001 water penetration banding. The test is based on an external windspeed of 13m/s with 75mm/h rainfall projected onto the front of the louvre panel. Whilst these bands have quite a wide range, they will at least give you an idea as to what class of louvre you need. Local weather conditions and topography naturally vary from place to place, so it is important to take into account your expected site conditions and compare that with the louvre test conditions.
4. Where are you installing your louvres?
The building location, position and exposure of louvre is also key.
5. How do you know the louvre you have chosen is right for your project?
We advise that you compare the simulated test results with your expected site conditions, since in reality simulated tests are never the same as actual site conditions. It’s also worth noting that a louvre with a Class A rain defence classification rating at 0m/s may not achieve acceptable rain defence performance even at 0.5m/s. Check the full range of face velocities the louvre is tested to, in order to ensure the louvre will achieve the desired performance for your specific design and site conditions.
It is worth noting that the BS EN 13030 : 2001 tests are based on a 1m x 1m test sample only, so for larger louvre panels you will need to consider how collected water is drained to prevent re-entrainment.
If you bear these questions in mind when selecting your louvre you can’t go too far wrong. However if you are in any doubt or could do with some advice or technical support get in touch with the global Louvre experts on +44(0)1296 652800 or sales@c-sgroup.co.uk
