How many holes?

[JG's Ghost]

I have a 6 inch, 360 cfm fan attached to a carbon scrubber matched to the fan that will be sucking air from the flowering room. The room is 8' x 8', and on the second floor of a warehouse. The floor itself is made of 2x10 beams covered with 5/8ths plywood on the upper side(floor of 2nd floor), and the same on the other side (ceiling of the first floor). So that gives me a gap of approx. 10" between the ceiling on the first floor, and the floor on the second floor.

If I feed the ducting into that gap how many 2" holes would I need to cut on the 1st floor ceiling side to accommodate 360 cfm?

I realize with the carbon scrubber it will be less than 360, but am just looking for a rough guess, or better yet a formula that I can use.

Thanks

JG

 

[FreezerBoy]

Intake should be 2X exhaust. Punch 3 holes of equal size. One at the top for exhaust, two at the bottom for intake.

A=∏r². A six inch hole's area is 28.26. Exhaust is 56.52. Area of a two inch hole is 3.14. 56.52÷3.14=18 holes. What's easier, cutting two exhaust holes or 18?

 

[JG's Ghost]

These holes will be for exhaust, but you did give me the answer I needed, and I may be able to go with larger holes.

Thanks

JG

 

[JG's Ghost]

Just rereading your post, and it confuses me a bit. If I want to have negative air pressure in the flowering room shouldn't the exhaust be larger than the intake?

JG

 

[FreezerBoy]

Negative pressure comes from increased air flow. Choking the intake reduces airflow and thus reduces negative pressure. Increasing intake increases airflow and thus increases negative pressure.

Negative Pressure for Dummies

 

[rives]

Choking the intake reduces airflow and thus reduces negative pressure. Increasing intake increases airflow and thus increases negative pressure.

This isn't correct - reducing the airflow will result in a higher vacuum condition (higher negative pressure). The larger the inlet, the lower the velocity of the air movement and the lower the vacuum condition. Visualize the negative pressure at the inlet to your shop vac vs standing in the doorway of the room that it is running in (assuming it is blowing out some other hole).

 

[FreezerBoy]

I may be wrong on which delivers the greatest negative pressure but, choking intake reduces airflow, stresses the fan and greatly increases heat inside the cab. I made do with a single intake and a 150. Upgrading to a 250 turned the cab into an easy-bake oven. Doubling intake increased airflow and increased cooling, converting the cab from a death chamber to a growth chamber. In winter months when extra heat is desirable, I choke off an intake.

Even with double intakes, the fan ramps down every time I open the door and ramps up when closed. Many here do 3X intakes. Some swear by 4X. 2X intakes are not required, it's just the easiest solution (like 12/12 for flowering). Whatever you use to cut the exhaust, use it twice more at the bottom. No math, no formulas, no swapping tools.

 

[JG's Ghost]

So. I have 360cfm being sucked out of the room through a 6" hole then I would want at least twice that size hole(s) for intake?

I know this is a simple problem, but for me it is critical. If I end up with a higher air pressure in the room then smell will get out.

JG

 

[rives]

As Freezerboy said, the rule of thumb for these applications is to double the inlet area. Reducing the area will tend to restrict the airflow, and that restriction is what gives you negative pressure. The downside of that is that you lose cooling volume. There is no way that you will wind up with higher pressure in the room even with much larger inlets if you don't utilize an inlet fan - you would need to have more inbound volume than outbound volume, pressurizing the room and forcing contaminated air out.

You could experiment with some kind of a throttle plate on your inlet hole(s) so that you could get the volume of air that you need to cool things properly and still maintain the level of negative pressure that you feel safe with.

 

[Granger2]

Ghost,
There are many possible solutions. If I understand your set up, the last thing I would want is forced air intake causing air to escape uncontrolled or out the door when you open it. I recall that you are concerned with odor control.

You can argue terminology, but I would opt for lots of air flow. Not only will you fan be happier, temp easier to control, but odor won't flow up airstream. If you want to slow it down some, get a speed controller. First, check your fan literature to see if they warn not to use a speed controller. Then buy a shownuff speed controller, not a light dimmer. Dimmers are unsafe with centrifugal fans. Have fun. -granger

 

[FreezerBoy]

Any of our fans can suck more air than dual passive intakes provide. That's a good thing. A certain amount of choke is required. 2X the exhaust is not required, its just the easiest "One-size-fits-all solution". Think of it as Ventilation For Dummies.

Like 12/12. Few, if any, strains need 12/12 but, all strains respond to 12/12. Do you need 2X intakes? No. Are they the easiest, fastest, math free way to get where you need to go? Yes.

Now, if you want to figure out the bare minimum, that's Ventilation For Smarties. I can't help you there except to point you towards Ventilation 101 and Understanding Airflow

Break a stem

 

[Scrappy-doo]

All 3

 

[JG's Ghost]

Thanks guys:

All I'm really concerned about is that I'm sucking more air out of the room than is being pulled in by passive means (holes).

As far as temps are concerned I think I have that covered with a 12000 btu water chiller, and an icebox light cooler hooked to another 360 cfm fan that will just recirculate the air in the room. It will not only cool the light (1000 watts), but work as a mini a/c unit for the room.
I've tried this once before with a DIY water chiller in a 5' x 7' room, and it worked well with no controller. Now I have a controller and a real 1hp water chiller, and expect to be able to adjust the temp in the room to whatever I want.

Thanks again

JG