I have a constant volume AHU with a steam preheat coil...The existing DDC system keeps the valve closed during unoccupied mode with the OA dampers closed and RA dampers open of course. The only time the steam valve fails open is if there is a freeze stat trip. DO you think it's better to just fail the valve open whenever the fan is off? The freeze stat is interlocked with the fan starter. Is it ok to leave the steam valve open all night with the fan off?