Negative pressure in tent

White widows…i just flipped 2 days ago

Nice, I have done Black Widow, and understand it is very close. It is one of my favorites.
You will be amazed with the changes, you are about to wittiness.

Two AC-I-Cloudline Controllers 67, independently control flower and veg tent.
Veg tent on right, less lights and cooler. A different configuration (T-6 Exhaust fan elevated) had less performance (Blow thru?). This configuration allows coolest air to rise thru flower tent (good thing).
At night (lights off), I can program cycle fans, with Temp or Humidity triggers available. Black spray paint inside reflective tubing with previously mentioned bends, cuts lighting. I have a box with cut-outs over the T6 fan on right in veg tent. Hopefully, no light transfers. Window has plumbing 90-degree hardware.

Been on a roll with challenges…description says good plant for starting out lmao

Nice… if this grow goes well I’ll try that setup when i add a seedling/veg tent

I agree. i forgot to use math training. SQ Area=(PIE) R exponent Squared
or 4"/2 (D/2=R)xRx 3.14= 2x2x3.14= 12.56
and two 4-inch intakes are less than one 6-in intake (6/2x3x3.14=28+).
I purchased 4 in tubing for the rear of the tents and found the holes too small for 4" tubing, So I thought,
two 4’s would work for negativing a six exhaust. The loss of cooling control necessitated swapping in a 6" tube for intake. Locating the T6 fan on bottom of veg tent for cooling flower from bottom provides better control with Cloudline 67 controllers.

I have a small 2x3 tent with both 4 inch intake and exhaust fans. Last year I changed the ducts from 4 to 6in. Kept the same fans, and just changed the ducts and tent flanges. Wow, what difference now I can dial up 3 times the air flow.

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Following up on yesterday’s discussion. I looked up an online ductulator.
I plugged in 100 cfm, since my 4 inch fans are rated at 120 cfm. This can be some eye openings info here. As this screenshot shows, if just hooking 15 foot of flex duct to the fan. The size would need to be 5 inch, in order to carry 100 cfm.
If anyone wants to use this, you will need to plug in .04 - .08 for the friction rate.

Hey @DEEPDIVERDAVE, the ductulator may be a bit easier than the formula that you shared with us yesterday, just saying.
Your drawing of the two tent set up has changed since the last time I saw it. This appears to be a good approach that you have come up with. How is it working for you?

I agree.

Correct. Multiple revisions resulting from attempts to improve air environment.
Rev 1 The Vivosun intake was replaced with an ACI-Cloudline T6 (Superior control with 67 controller) and much less noise.
Rev 2 The back of the tents could support a cross-over, so I ordered some 4-inch hose. The hose arrived and is too big for back of tent smaller opening. Couldn’t use the 4 in as planned.
Rev 3 The coolest air available is from outside and I have an extra supply of 4-inch hose. No Brainer, use the 4-inch and make a window intake.
Rev 4 The window intake provides cool outside air into the veg tent. Good plan until the T6 intake (split into both tents) defeated window intake performance.
Rev 5 Reading many postings on fan configurations, brought the idea, T6 inside the Veg tent (pulling from twin 4-inch outside window intakes. T6 Veg tent exhausting from top of tent into flower tent connection (shortest route for connection tubing). Top of tent has hottest temps, theory.
Rev 6 Configuration temperature and control trials resulted in higher and harder to reduce temp issues.
Rev 7 Changed window intake from 4-inch to 6-inch.
Rev 8 Temp and control issues still perceived. Moved T-6 intake to bottom of veg tent for blowing into bottom of flower tent. Temperatures lowered and easily controlled using 67 slow speeds 1-3. Night operation for lights on clearly supported in avoidance of daytime temps.
Ten days of 12/12 and I went to 18/6, growth seen and flowers looking good for starting cola’s.
Rev 99 Impending, i am sure. Forum postings mention air volume vs distance for negatively influencing performance and reducing air flow. Window needs another 6-inch intake from outside for summer operation. Flower tent gets coolest air fro veg tent and air rises thru crown for top of flower tent exhaust.
Flower Tent Day temp kept below 83 degrees with 80 and speed #1 settings on both T6 fans (intake & exhaust). Midnight to 7am Intake 67 Controller can be set Min Zero and Max Two with Auto engaged (Temp/Humidity monitor triggers). Flower/Veg tent night temp 60-65 degrees.
I appreciate the forum contributors for their comments and assistance. Ten weeks into this first grow in many years. All new and foreign (forum, equipment, and support available).

I would put a fan in ur tent

@DEEPDIVERDAVE, Wow, that is quite an evolution of ideas. Good job, doing more with less there. You must have the ability to stick too the desired goal. I would had gave up somewhere around rev 2, and just used two fans on each tent. It also sounds like you like automation.
Just a word of caution here. If you are using outside air to cool you tent. The tent will not be any cooler than the outside temperature. No matter how much air you push through it. If you are in a location that gets into the 90s your tent may end up over 100.
Remember that heat will only flow downhill, (That is from warmer to cooler). In order to move heat uphill, (From cooler to warmer), you need an energy source to do it. Such as an AC unit.
When I used to cool large buildings. It was necessary to switch from cooling with outside air to mechanical cooling. Somewhere between 55 - 70 degrees outdoor temperature depending on the humidity.

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