Vivarium air flow

[orchid_guy]

I am new to this forum, so please forgive me if I am addressing my question to the wrong group or if my topic has appeared in another similar thread.

I am building a vivarium to house some of my orchids, but am not clear about air flow/ventilation.

I am planning to install 2 fans at the top of the vivarium, under the lights. (50 gallon aquarium).

One fan will blow air down, and the other suck air up and out. Is this setup appropriate?

Is ventilation the same as air flow?

And do I leave the fans running all the time, or set to a timer?

I have looked on the web, but have seen nothing that specifically talks about this.
Any help would be greatly appreciated.