High humidity - exhaust fan too big?

[Custom45]

Hi
I have a grow room about 2m x 1.1m, 2m high. Four plants in there in late flower in airpots. 2x 300w led lights.

I have an 4" intake fan pulling fresh are in at the bottom, a 6" rvk exhaust fan at top supposed to be taking out warm humid air and two 7" oscillating clip on fans blowing over top of canopy.

In this hot weather I also have a portable air conditioner unit.

Problem I'm getting is constant high humidity, late 60s/70s. I have a large dehumidifier running which makes little difference. I've thinned fan leaves out to allow plenty of airflow around buds and light to penetrate further down, but still getting high humidity.

I find sometimes turning off exhaust fan actually helps to lower humidity. Sometimes it doesn't, same with intake fan.

Any thoughts? Is my exhaust fan too powerful for the space? Seems to be a lot of negative pressure, like the door to the grow room pulls itself shut when the fan is on.

 

[DanC520]

It’d raise humidity if air outside the tent is more humid than inside. Idk how that’d be possible with a duheuy and ac going.

I don’t think it’s negative pressure related. I know all my tents would see rh skyrocket if I turned off exhaust completely. I don’t run intake fans, but don’t see why those would play a role. My approach is to keep lung space drier and cooler than inside tents. Exhaust triggers on temps and rh. Once surpass a set level, fan kicks on and pulls in the drier cooler air.

 

[Moe.Red]

Need to know the RH and temp in the lung room you are pulling air from into the tent.

Is the AC and Dehey in the lung room? How big is the lung room?

For this exhaust system you have, it is essential that the lung room be cooler and lower RH than the tent.

 

[Madmax]

Are you outside in a shed getting fresh air from outside or in a room..i turn my exhaust down so the dehuey can work cause all your doing is pumping more rh in.what temp is your room as higher the temp the lower the rh will b..see if you can find a balance

 

[Custom45]

It's a shed that's split in two, one half insulated and boarded out as grow area, the other half just a shed (lung room as it were), with air vents.

Aircon and dehumidifier are in grow room. Intake fan draws are in through carbon filter from lung room side into grow room side.

I've put a monitor in lung room to check temps and humidity. Aim for 25⁰c with lights on and 20⁰c lights off in grow room.

 

[Custom45]

Also, my 2 fans are blowing from slightly above and down onto canopy, should I position them to blow just below and up through canopy instead?