New 315 LEC too hot

[PuravidaC]

You are correct that exhaust cfm should be greater than intake in order to maintain negative air pressure in grow space. I am using a passive intake which should be 4 times larger than exhaust.

 

[Aloner]

Oh, I see. I misunderstood that part of your post. So if your exhaust is, say, 6", you want about 24" for intake? Good to know, thanks!

 

[DrPhoton]

Its the airflow not the size of the hole.

 

[Aloner]

So how do you measure the airflow from a passive intake?

 

[DrPhoton]

To pressurize a room you need to offset the pressure only slightly to create "pressurized airflow", whether thats positive or negative. For negative pressure you pull more air out of a room than you let in, by limiting the size of the passive intake you restrict ever so slightly the ability to bring air back in as fast as it can be forced out.

The size of the passive intake is not dictated by the size of the active exhaust (the diameter of the hole), this is a basic rule of thumb that could get you into trouble. Its dictated by the flow rate of the active exhuast. With a static sized passive intake, the more air that is sucked out of a room by the exhaust, the higher the negative pressure is going to be. The more air that is pulled out, the harder it is for the active fan to maintain pressure as the fans motor is rated to only handle static pressures of a specific range.
A high airflow active exhaust will require a larger passive intake to maintain ideal pressure, a low airflow intake will require a smaller passive intake to maintain similar pressure. The airflow rate of the active fan is also dictated by the size of the environment, the more space there is, the more air the fan has to move to meet the minimum replacement rate.

Grow tents typically have 6-8" ports regardless of the size of the tent. However you can open more ports to allow more airflow to maintain ideal static pressure with larger tents.
If passive vents are too small, a fan that needs to cycle the air the recommended 2-3 times per minute would create too high of pressure and also strain the fans motor. Too large of passive intake would not create a high enough negative pressure and prevent ideal airflow.

 

[Aloner]

Phew! I've read some of your dissertations on light as well -- you can't stand to give a straight answer, can you? Seriously though, thanks. I guess I need to do some more research on the subject.

 

[DrPhoton]

No i cannot, sometimes i do. But usually i will go into more detail than i need. I just prefer it that way.
I have edited my previous post so i would suggest a reread. However to sum it up.
The size of the passive intake is dictated by the volume of air inside a room. More space means the ventilation system needs to process more air to maintain the recommended air replacement rate. The adjustment of the passive intake is to maintain ideal negative pressure.

There are formulas to calculate the passive intake size based on flow rate and room size. However i have none on hand.

 

[Aloner]

lol still pretty inscrutable but thanks for taking the time!

 

[DrPhoton]

No worries, perhaps you might want to learn about temperature and pressure, and the physics of it. Getting your head around how the air molecules are effected by such factors, really helps you understand pressurization and the coherence of the molecules.