If that's a complete sentence, then no. There is no sense of who or what is being talked about. Now, if it said "Everyone in the room is cool" then that's a perfectly good sentence. Or if you are talking about the room itself, then "The room is cool" would work.
The problem is that this sentence does not have a subject. English is non-pro-drop language, in which the subject cannot be dropped, unlike other languages, such as Spanish or French. Here, it is a dummy pronoun or expletive.
So you can say