🌱 I have an opening in my tent for cool air to come in from the room, then at the top on the other side I have an exhaust fan pointed out which vents hot air out a nearby window. So the fan pushes out hot air, and that passively draws in cool air from the room. Since the exhaust fan is really strong, I can see that the plant leaves all start rustling when it's on as long as the tent door is closed, so I don't even have any other fans in the tent.
If the humidity or temperature is dropping too low with the fan on 24/7, you could put it on a separate timer from the lights, and then set it to go on and off every hour at night or something like that. I know with my mechanical timer I can have the power turn on and off as often as I want. After fiddling with it for a few days, you can figure out how often the exhaust fan should be on in order to keep the temperature/humidity as good as possible. If the fan is just overall too strong, you can also get something called a "Speed Controller" which works with most fans to turn down the power.
A carbon filter doesn't cool anything, but it will "scrub" odors from the air that passes through it. In fact, they actually make your exhaust system a little less efficient because the air has more it has to go through. But it's worth it.
You want the carbon filter in the tent hooked up directly to your exhaust in some way, so that all the hot air is getting passed through the carbon filter, and then out the window. That ensures smelly air doesn't get outside. As long as the grow space is sealed, then the negative pressure from the exhaust fan should keep any air from spilling out, which also prevents smells from spilling out. If you do it right, the only time you'll even smell weed is when you open the grow tent door, since that releases the negative pressure and the smell can drift into the room.
Here's a little
tutorial about using carbon filters with exhaust systems and how to set them up.
If possible, could you post a picture of the whole setup with the plants inside so we can see if there's anything that might make the venting system work better for you? 🌱