This short blog post will go some way to explaining the louvre rating system and how you can use it to find the best solution for your building.
As we have said before when specifying louvres you should take into account the needs of the building. (Read our Guide:How to correctly specify louvres for more information) So before diving into the numbers make sure you know what will be kept behind those louvres and how much rain penetration is acceptable.
Once you know that you can move on to the test data.
In most louvre brochures reference is made the HEVAC/BSRIA or BS EN 13030:2001 test method which is the industry standard for weather testing louvres. This tests louvres in 3 key performance areas and allows specifiers to relate one manufacturer’s performance against another:
- Discharge Loss Coefficient
- Overall performance
Louvre Effectiveness (or Penetration class)
Describes the louvres ability to prevent rain penetrating the louvre. A louvres effectiveness is given a class rating from A-D, A being the most effective at preventing rain and D being the least. Each class offers a maximum allowable penetration of rain in l/h. m². So to achieve a class A effectiveness rating a louvre must not allow more than 0.75 l/h. m²
Discharge Loss Coefficient (or Airflow Class)
Describes the airflow characteristics of the louvre, the higher the coefficient, the less resistant the louvre, i.e. it allows air to pass more freely through the louvre. The louvre is then given a class rating from 1-4. 1 being the least resistive to airflow and 4 being the most resistive to airflow. Specifying louvre is always a compromise between airflow and water ingress, generally you find the more weather resistant louvres have a higher airflow resistance, but this isn’t always the case as the CS RSH-5700 demonstrates.
This is determined by multiplying the louvre effectiveness by the coefficient. We recommend that this is not used as the sole determining factor when choosing louvres as it can mask poor weather performance on a louvre with good airflow.
So to summarise, when comparing louvre models use the Louvre Effectiveness Rating and the Discharge Loss Coefficient, if they aren’t mentioned, ask the manufacturer for them.
- Give us a call on 01296 652828 or email firstname.lastname@example.org and talk to us about your louvre needs.
- Read our blog Building & Architectural Louvres Explained
- Read How to Calculate Louvre Pressure Drop
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