I've got a church with a few old "Nun's Cap" type roof gravity vents. In my opinion they were remnants from the days of natural ventilation during cooling season. The church now has A/C. The arrangement, I am told, (the ceiling it is above is over 20 feet in the air and I have not seen above it) is that the space above the dropped ceiling is an RA plenum and that there is no insulation and that the openings to these nun's caps are open to that plenum. The building has gas fired hot water baseboard heating and split system DX A/C with no outside air to the units.
My question is, are these gravity vents even necessary? In my opinion they are not, but am I missing some reason to keep them?