The only situations for which well-defined criteria exist is for giant commercial chicken barns (meat chickens, and layer batteries). For those, for ammonia and humidity removal purposes you need 4 changes per hour; for cooling in the summer it can be up to 40+ changes per hour.
I do not believe this has much of any relevance for the home coop, though, unless you are keeping your chickens in really industrial-type conditions (very crowded and horrible).
For one thing, amount of air exchange that's required will depend GREATLY on the number of chickens per volume of coop (yes, volume in this case, not square footage), so that more-crowded coop needs more ventilation (airflow goin' on) than a very uncrowded coop. Also, your sanitation practices make a big difference -- having droppings boards under the roosts that you clean every morning makes a BIG difference in ventilation needs, IME.
My advice remains as per my ventilation page (link in .sig below): build LOTS of ventilation, then if you have to close some (not all!!) of it down in cold weather you certainly can. Nothing bad ever came from having too much ventilation available.
The other reason btw that I think "changes per hour" are irrelevant for a typical home coop is that it is IMHO a very bad idea to design your coop such that it depends on forced-air ventilation, which is the only thing producing *consistant* airflow numbers. A well designed passive ventilation system (i.e. air flows on its own thru openings in walls) is much better in many ways, but actual airflow will vary with the weather etc.
Good luck, have fun,
Pat
