Negetive pressure tent & humidity

[TripleCchronic]

To acheive negetive pressure I have a vivosun 6 inch inline fan exhausting my 36"×20"×62" tent. Im having an odd issue where when the tent is closed, even with my humidifier its rh wont go above 40%. The rooms the tent is vented into does not get humid either and theres not condensation in the tent or water on the floor. But as soon as I open the tent the humidity rises to the rh my humidifier is set to. I decided to leave the tent slightly open yesterday and both the tent and the room it vents into came up to the rh my humidifier is set to. Is the negetive pressire effecting the cool vapor my humidifier produces to not be able to stay airborn? And if so where is the water going?

 

[The Celt]

You have too much airflow, your fan is sucking the water vapour out of the tent.

To give you an idea, I use positive pressure down draft setup. In a 4x8 tent with 2 - 630w CMH lights, my 6“ fan runs at its lowest speed and keeps my tent about 85F.

I run a 4“ fan in my 32”x32” tent and if it was variable speed, would turn it down to.

 

[TripleCchronic]

Im getting a 4" inline booster fan for intake. My 6" inline is in its lowest setting. Also where im confused is if the fans sucking out all the humidity then why isnt the room its venting into humid?

 

[BubbleBucketz]

Is negative airflow mainly for keeping smells in? I run positive in my tents but smell isn't a problem for me.

 

[The Celt]

Moving air is less able to hold water vapour and the faster it moves the less it can hold.

You say it vents into a room, but is that room closed off to the rest of the house? If not, you are effectively trying to humidify the whole house.

 

[TripleCchronic]

Yes it is.

 

[TripleCchronic]

When the tents left open even a tiny bit the room it vents into and the tent come up to the humidity set on my humidifier though?

 

[BubbleBucketz]

I feel sorry for the stealth growers. I couldn't imagine the pain it is to keep the smell in one room. Good luck on this and your grow.

 

[The Celt]

Not sure what to tell you mate, but 40% humidity is not a bad thing, just means your girls will drink more water.

Humidity in my grows tend to run between 35 - 55% and I never worry about it. When it comes right down to it, most strains today are hybred with a lot of Indica influence and Indica hails from arid regions.

 

[BubbleBucketz]

Yea my RH stays in the 35-50% range as well. Spikes to 60% sometimes with lights off. I tend to have no problems with it.

 

[TripleCchronic]

Oh ok. I guess humidity isn't as important as I though in veg.

 

[BubbleBucketz]

Oh ok. I guess humidity isn't as important as I though in veg.

The only place and time I keep an eye on my RH is when I am in flower....

 

[iNeedMeds]

When the tents left open even a tiny bit the room it vents into and the tent come up to the humidity set on my humidifier though?

The sensors in humidifiers don't have pressure compensation. Since the water holding capacity of air increases as density and pressure decrease, creating a vacuum and increasing air speed increase the water holding capacity. It's the reason why a fan can cool our bodies, as the moving air has lower pressure, and therefore can evaporate sweat faster.

Long story short, the sensor sees a capacitance and temp, and thinks it's at 50%. In reality, the air speed and vacuum are tricking it, and you're ending up with lower humidity.

You can reverse this effect by pressurizing your tent, and creating vacuum on the room around it to control smells. This is a much more effective method for controlling odour anyways.