DonJones said:
If you are going to use the area between the rafters for fresh air intake, that is gong to be the hottest air of anywhere in the basement. For a grow area the size of yours, one cold air return cover over a 8" high hole between 2 studs in the new wall will provide all the fresh air you will ever need via negative pressure like you are talking about doing through the rafters and it will be cooler air in the summer. If you go to Home Depot, they have crawl space vents like the one in my picture here that have screen in them to cut down on insect movement, which your open rafter thing won't do. If you decide to stay with the open rafters at least get some window screen and screen them.
Great point regarding having the passive air intake be LOW, rather then high, due to the fact that hot air rises, therefore a passive intake via floor joists = warmer air. How about this as a solution. In my layout diagram, fan #2 will be mounted HIGH on the partition wall, actively expelling mostly warmer air into the rest of the basement. I will then take either heavy duty plastic and cut it into square shapes, and staple them in between each of the floor joist areas, or heavy duty garbage bags and do the same thing. While this will hardly be air tight, it will allow less air to enter through the floor joists, then I will have a LOW hole on the partition wall(s) for a passive, colder air, intake. I can make two passive intake holes to guarantee a cumulative higher opening of passive air intake compared to any cracks/floor joist areas not sealed with the stapling of plastic material in the floor joists and put those crawl space vents over them you mentioned from Home Depot. I have a screen I can cut into squares and staple to the partition drywall/in between studs, to try and limit particle/insect entry due to airflow (them being blown in). I did however get my whole house/basement sprayed by the bug man, and have not seen in a live insect, save for a few spiders, ever in my house, but who sees/looks for spider mites for example prior to growing?
As for the light, my basement is unused, I can guarantee that no light will be on the basement PERIOD, there is no 'switch' just three pull-chains with bulbs in them, none of which are near the grow room. There is however windows but the light that will come in will not be able to truly get in the grow room, if for some reason a modicum of light does, I will eliminate it, to the point of putting cellophane sticky material over the windows, or simply put towels/blankets over them, they are small windows, and none are close to the grow area, the closest one being by the circuit panel (see diagram, or pictures page 1). Due to the awkward ducting, the easiest approach, is where I have the partition now, it does limit the length of the room to 8 feet, I am fine with that for now, I am only growing for myself though, a few Lbs will go a loooooong way. And finally, a full size door is a must for me, so I can go in and get out easy, luckily by my dryer is a full sized drain, as well as hot/cold water faucets, so not much hauling of water. Finally, I might want to go buy the knob myself, as I take it the handyman (who is getting the studs, door, drywall, nails) will not get a locking door knob for an interior door. I also will e-mail him telling him I need a full-sized door, just to clarify the point. I bought the ducting, which is 6" insulated, to reduce noise of the wh-o-o-o-o-o-sh from the longer ducting, and the intake/exhaust vents, because those are hard to find locally in 6" size, I had to order them online.
So in summation changes to ducting for active air exchange:
1) Partially-seal with heavy duty plastic/garbage bags in between the floor joists by stapling, achieving a total air-seal will not be possible short of putting wood/caulking in there or dry walling across the ceiling (like a normal upstairs ceiling), I want to avoid this for two reasons, the first lowers the usable height of the room, and two, radiant heat? So the objective would be to make the floor joist air penetration less cumulative entry space then the passive air intakes.
2) Have an active 6" exhaust, being powered by a 409 CFM fan blowing air out of the top of the partition wall, left side of the door. By positioning it high on the partition it will be more warm air, as opposed to cooler air which will be closer to the floor.
3) Have two to three 6" passive air intakes, positioned on the left-right of the door (partition wall). Negative pressure will bring in more cool air, due it the hole being closer to the floor rather then the ceiling.
I guess the only question then is:
Is my approach to sealing the floor joists as a passive (warmer air) intake remedied by my plastic/bag partial-sealing approach? Obviously it won't be anymore near air-tight, but if it makes the cumulative area less then the passive intake holes on the partition wall, will it be negated due to physics of negative pressure?
I can take pictures, or draw a diagram if any of this is not clear with my words.
Thoughts?