It's called a lung room. Google it.
I've mostly heard the term lung room used for sealed systems. In that set up you have air coming out of it and going into it. From what I gather, FFF is talking about using it only as a pre-treatment for air.
A tent filled with air has very little thermal mass. The basic concept works, but your equipment will be cycling like a mofo unless it's a big tent. Putting some 5gal buckets of water inside would improve things a bit.
The other way of doing this is to seal it and make it a two way lung room. Those work... on the other hand, don't use CO2 in your bedroom. No really, just don't.