As a ventilation system a Zehnder ComfoAir 350 is in use.
The ventilation system is connected with openHAB via a serial port which is normally used for the maintenance access. It is directly connected to the serial port of my server. Currently I can't answer if it works with a "RS232 to ethernet lan adapter". Just try and let me know if it works.
Since the communication protocol is very well documented by the community, you can use it for your own control software. I developed a binding for openHAB which allows me to control and analyse the ventilation system.
By openHAB rule engine following functions could be implemented.
More information and links about the binding can be found on my ComfoAir page.