How big is the room?
How powerful is the dehuey?
Exhausting air from the grow area? To where?
Where does the fresh air coming in, come from?
Mine set on the ground in closed rooms. I also use a greenhouse thermostat switch, that turns on exhaust, and pulls in fresh, filtered, cold air to help the cooling in these colder months. In about a month all cooling units will be off and all cooling will be done by these thermostat exhaust switch's....RH in cold winter air is way low and my dehuey's almost stop working for the season.
I then have to run the high pressure booster pump on my RO unit to keep me in needed water amounts, daily...
If your exhausting the heat some way. You shouldn't be getting much RH build up.....UNLESS the room the grow draws air from is high RH.....
The source of your fresh air maybe where you need to control your RH first....