The seat back is drilled with holes, the seat back is also the front of the wheel well. The air moving under the vélomobile accelerates into the wheel well creating a low depression zone just like the diffuser on a car and so the air in the cabin is sucked out through the seat. I have been driving with a dry back in quite warm weather, it is a bit strange at first but you get used to it The cabin is quite large and the system has no problem renewing that volume of air in a very short time.
Die Lösung finde ich ebenfalls klasse. Ist die Hupe denn laut genug?
So far in town it is loud enough. I have yet to try it on the road - the only time I would use it is to signal to other cyclists that I am coming past.