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This European Standard specifies a method for measuring the water rejection performance of louvres subject to simulated rain and wind pressures, both with and without air flow through the louvre under test. For the purpose of tests in this standard, a 1000 mm x 1000 mm section of weather louvre or the nearest possible blade increment is considered. Weather louvres are designed to restrict the passage of water during rainfall while allowing the passage of air into or from an air distribution system or part of a building. They are used in a wide range of applications, where there may be differences in wind speed and direction, levels of local turbulence, rate and droplet size, distribution of rainfall and surface water flow from the surrounding structure. It is impractical to consider a standard test procedure simulating the whole range of likely conditions, but this standard provides for heavy rainfall directed on to the louvre surface, with simulated wind pressures. This provides a common basis on which to compare the water rejection performance of weather louvres of different designs. This standard is not intended for the evaluation of weather performance of pressure relief dampers. The purpose of tests incorporated in this European Standard is as follows: a) Weather tests To establish the weather louvre effectiveness when subjected to wind pressure at various air flow rates. b) Discharge and Entry loss coefficient/Pressure requirements To establish the air pressure loss through the weather louvre at various air flow rates and by calculation the Discharge and Entry Loss Coefficient.