It is used to switch on/off and change the speed of fans which are based on multi-speed motors.
Airstream 2.1
A continuous running centralised single flow ventilation unit (airstream) extracts the stale air from different rooms contemporaneously, with top acoustic comfort. To be used in combination with self-adjusting air inlet. Thanks to the easy-to-fit air distribution system each single ambient can be properly ventilate.

