Humidity switch for gas and electric clothes dryers.
The hot air exhaust should be connected to a pipe in shape of letter Y. One part of the fork is further connected to a pipe that leads to the outside of the building.  The other side of the fork is connected to a pipe that leads to a barrel lint filter located inside the building. Before the hot air reaches the fork it encounters a switch operated by a servo-motor. The servo-motor itself is operated by a combination of adjustable temperature meters and a humidity meter. For example;  when the temperature of the exhaust air is low and the humidity high the switch opens the passage to the outside of the building. When the humidity of the exhaust air is low and the temperature of the exhaust high, the switch directs the air flow to the inside of the building. Of course, working of the switch is influenced also by the temperature outside the drier; when the temperature inside the building is high all the air from the drier is directed towards the outside of the building.