I would imagine a lot of it depends on the climate. For instance, if there is a monastery in New England, summers may be very uncomfortable, but the heat would not be detrimental unless there were additional factors (e.g.: illness) that could effect it. However, if there is a monastery in the deserts of California or Arizona, where it could easily be 110+°F on a summer day, air conditioning might be a necessity to stop heat stroke, dehydration, &c.