External weather louvres are externally mounted air transfer devices for the fresh air and exhaust air of airconditioning systems. They are installed in external walls and façades. Their narrowly arranged blades give goodprotection against the direct ingress of rain as well as against leaves and birds.
Under certain unfavourable conditions, such as heavy rain, and depending on the airflow velocity it might happenthat slight quantities of water enter together with the air. This is why the airflow velocity in fresh air openingsshould not exceed 2,5 – 3 m/s.