Air Exchange Rate
The key is determining the volume of your bus then calculating the number of exchanges that can occur in a given period of time. For example, my bus has 1175 cubic feet slap empty, subtracting the volume of any large items (counters/storage/benches/etc) provides a more acurate result. At 40 CFM it would take almost 30 minutes to exchange all the air in the bus, theoretically. With two fans (properly located) I could get more than 4 exchanges per hour. The target exchanges/per hour is up for debate as I don't have any guidelines there; however, 4/hour would probably go a long was to prevent excessive heat/moisture build-up. In greenhouses exchange rates can be as high as 60/hour in the summer and as low as 2/hour in the winter, but these are not really comparable figures. Hope this helps!!!
1985 International 28 Passenger
6.9L Diesel/Allison AT-545