Ventilating 2-Chamber Tent with 1 Fan

[stratagem]

Here is what I was thinking. Let me know if it's possible or how I should tweak it.



I need to vent the two sections of my split tent (made from B&W Poly) and I figured since neither section is all that large I might be able to get away with a single 4" or 6" centrifugal fan. The tent will be inside of a closet with ducting that would tie into a roof vent also being used by a dryer unit to exhaust heat. I'd use something like this:

1. Can I get away with a single centrifugal fan? Or would I need to individually ventilate each section?

2. How large of passive intakes would I need in vegging section and from vegging to flowering?

3. Should I go 4" or 6" for fan and ducting? Vortex seems to be pretty popular, any other recommendations?

4. If I ventilated the vegging section separately, do you think a PC fan on the exhaust and a slightly less powerful PC fan on the intake would do the job? I figured I might run into issues with this if I don't exhaust the heat out of the closet.

5. Do you think I can get away with 400 HPS or would 250 HPS be better for this size flowering area? (2'3" wide x 2'3" deep x 5'6" high) I already own a electronic ballast for 400W HPS. But I was looking at the HIDHUT 250W interchangeable eBallasts.

 

[stratagem]

Anyone? (bump)

 

[stratagem]

Don't make me beg peoples.

 

[Nicoli]

You've got it figured out. I'd go with a 400 though for your flowering space. The Splitter will work fine to exhaust both tents. Just make sure you use a big enough fan.. 6" vortex will cool 1000 watts easy

 

[stratagem]

You've got it figured out. I'd go with a 400 though for your flowering space. The Splitter will work fine to exhaust both tents. Just make sure you use a big enough fan.. 6" vortex will cool 1000 watts easy

I don't want to run a duct to each section of the tent with the splitter. I suspect that would greatly affect air flow. I want to intake air from the room/closet into veg then continue that flow of air from veg to flower. The splitter is so I can use the existing ductwork running to the roof currently being used by the dryer unit which is directly adjacent to the closet. I'll put a hole through the wall from the closet to run the ducting through. I've updated my diagram to depict this better.



How much CFM does the fan need to be rated for? Both tents together are just over 43 cubic feet. If I want to get the temps down 10 degrees (if say intake temp is max 85-90 degrees but should be rare since I have central a/c) I'm guessing I'll need to move the total volume up to 3 or 4 times a minute. So now we're talking upwards of 172 CFM. But with all the ducting, possibly a cool tube (or ventilated hood) and the carbon filter can I expect a 50% decrease in air movement or MORE? Should I be aiming for around a 344 CFM fan or is that way overkill? I'd like to get one of those router speed adjusters and see if I can quiet it down a bit as well. Since the fan will be outside the tent at the top, I can probably wrap the fan in a box with noise muffling materials surrounding it.

Where is the best place to buy fans?

How large should the passive intake be? How about the vent between veg and flower? Double the ducting size or more?

 

[Norkali]

strata, I'm down to help you, but I'm just too out of it to really help right now and to deal with the numbers. I will be back tomorrow morning to answer your questions, but from what can see - it looks like you are set dude - good job doing the research work and sketch...

 

[inphu510n]

The ICMag Ventilation 101 thread absolutely rules for this kind of info. Should be able to find the info there.

 

[hush_free]

look like in ur pic ur only using 1 filter so the airflow from veg room wil flow much easyer than the fillter u could try and put a towel over the pipe in veg room to match up airflow

 

[stratagem]

look like in ur pic ur only using 1 filter so the airflow from veg room wil flow much easyer than the fillter u could try and put a towel over the pipe in veg room to match up airflow

I don't plan on having any ducts running to my veg room just air intakes vents. Although I'm undecided on the vents. I've looked at the darkroom louvers (But for $26 per? How much reduction in airflow is there?), standard wall vents (will they be good enough for light trapping?), and I've thought about multiple 90 degree PVC Bends (might lose too much space inside tent) like they do on wooden cabs but I'm afraid of how it might work on a tent with 6mil B&W poly. I'll be adding more cross-sections to my tent to minimize on the amount the walls of the tent will suck inwards.

I figured if I get enough surface area on my carbon filter, which I'll most likely make myself, and I properly size my vents then air flow shouldn't be a problem. Mainly I'm trying to get an accurate idea or really good estimate of how large of a fan I need and how large of vents (and which type) would suit my design best. Surely this will come with experience.

The ICMag Ventilation 101 thread absolutely rules for this kind of info. Should be able to find the info there.

I've read over this post but it doesn't specifically cover my design. I was hoping someone could explain why my design would or wouldn't work and help me figure out the specifics of vent sizing and CFM needs.

If I take the formula: CFM = 3.16*Watts/TDelta (let's say 10 since my dwelling is A/Ced when it's especially hot outside - let's say a range of 64F to 85F). So 568 watts for all my lights. I'm not going to count my fan since it'll be outside the tent. Although I'm not sure if it'll add extra heat to the closet. I'll also be adding a DIY aero-cloner which will means there will be a submersible pump. That's 36 more watts, but I'm thinking this won't affect my cooling needs much, if at all. So 568 * 3.16 / 10 = 179.488 CFM.

But how is this formula affected by two chambers venting into each other, with ducting, and possibly a cool tube/ventilated hood? Should I expect a 50% reduction in air flow and aim for a 360 CFM fan?
Would a 6" centrifugal fan turned down be more stealthy (quieter) than a 4" centrifugal fan running at full speed achieving the same air flow?

Let's say I go with a 6" centrifugal fan. Using the chart from Ventilation 101, that means I'd need a 7.5 inch square vent or use (9) 4" PVC pipes. And looking further down on V101, a 2-chamber design would use the same size intakes for the first chamber and for the section between chambers. Can I use these specs even though there will be a carbon filter and the vents are louvered or 90 degree PVC pipes?
How much air flow restriction is there on those 8"x8" darkroom louvers? Honestly, I don't want to pay $50+ for just vents anyway and I'm leaning more towards standard louvered vents from home depot with an added allergen filter.

Maybe I'm answering my own questions and just want some affirmation before I start buying $130+ pieces of equipment and cutting holes in my tent. Measure twice, cut once right? Or in my case, measure 1000x and cut once. I tend to over-analyze.

Perhaps I should be satisfied with Nicoli's response - 400 watts and a 6" vortex. Then cut my intakes and see how it works out. But I'm a greedy information whore. Heh.

Please quote my questions above.

Hey Norkali, I'm waiting on those number crunching skills!

 

[Norkali]

Dude I totally couldn't find this thread yesterday of this morning...gimme a bit.

 

[stratagem]

The Panasonic Whisper Fan Scrubber Tutorial just peaked my interest since noise is a big concern for me. The design of the carbon scrubber would help me gain real estate inside my tent as well. Removing the air from the closet all the way up to the roof will still need to be part of my plan. I'm hoping the length of ducting and bends won't affect air flow too much. Still reading through all posts in the thread but it looks promising.

 

[stratagem]

Dude I totally couldn't find this thread yesterday of this morning...gimme a bit.

Alright now I just think you're trying to tease me.

 

[Norkali]

Strata, you did the number crunching for me.... I don't even need to tell you this now, but your set like you thought. Sorry it took me so long to get to this, but I had a gnarly bit of work to do yesterday...

Go with a 6'' fan, ebay is good for fans. Vortex, Elicent, whatever floats your boat.

10% bigger intakes on each opening, so I'd go with the (black!) PVC elbows, and as you saw - plenty of them. Make sure that the flower intake is 10% bigger than exhaust, and make sure the veg is 10% bigger than the flower intake. I don't know exactly how much, but those louvers do take a big chunk out of CFM, so I'd personally stay away. Go with a High Output 6'' fan, to make up for the bends and static pressure. Speed controller is a good idea to adjust it if it is overkill. Next stop is the Canfan website to match up the CFM to which filter you want - even if your going with a homemade scrubber this will be massively helpful as you can then build your scrubber to the correct size/dimensions based upon CFM. It looks like your gonna be shooting for a Can 33 or a Can 50 or so....should work perfect with a High Output 6'' fan.

No on the PC fans, unless your growing in a shoebox, IMO. lol.

Let me know if you have any more questions.

 

[stratagem]

I appreciate everyone's help, thank you!

I'm leaning towards the S&P 5" TD125 or 6" TD150 since stealth will be a big concern for me. Hopefully the static pressure isn't too bad.

10% bigger intakes on each opening, so I'd go with the (black!) PVC elbows, and as you saw - plenty of them. Make sure that the flower intake is 10% bigger than exhaust, and make sure the veg is 10% bigger than the flower intake. I don't know exactly how much, but those louvers do take a big chunk out of CFM, so I'd personally stay away.

When you say 10% bigger, if say I go with the 6" fan and ducting, 10% larger than 6 inches round? So 6.6" round? And for the veg intake, 7.26" round? Obviously I'll need to determine how many 2", 3" or 4" 90 degree elbows I'll need by calculating area size. Actually, looking at the the ventilation 101 thread, the intake chart is indicating double the size, is this overkill then? And I'm looking closely at this chart now, and the suggested # of 1", 2" or 4" PVC seems WAY OFF. For example: Take the [Area Square Inches] of the 6" duct, which is 28.3. If i double that, it's 56.5, which is what the chart is suggesting as [Intake area square inches]. Now take the 56.5 and divide it by the 4" [area square inches] which is 12.6. That comes out to about 4.48. So how does a 6 inch duct equate to (9) 4" PVC elbows? (5) 4" PVC elbows would be more than double the area of (1) 6" duct. If you venture further into the posts, there is another chart that is more accurate HERE.. And Hoosierdaddy replies indicating the 10% is fine just as you have. Maybe I'm reading that first chart wrong, but there is way too much conflicting (or inaccurate) information floating around.

If I go with the 10% mark for flower chamber intake, then we're talking about 34.2 square inches needed for a 6" duct. So divided by 12.6 (area of 4" PVC) then that's about (2.7) 4" PVC elbows - round up (3) 4" PVC and I've got about a 34% increase. If I use 2" PVC elbows then we're talking like (10) of those but I could get closer to the 10% mark. If I can find 3" PVC, that's about 7.1 square inches of area which would call for (4.82) 3" PVC elbows. Rounded up to (5) 3" PVC and I've got about a 25% increase on the 6" duct for intake. Hopefully I'm making good sense of this math. heh. Sounds like (3) 4" Elbows or (5) 3" Elbows would be my goal here. I could also mix and match sizes to get closer to a 10% increase. And for veg intake, well I don't feel like doing any more math at the moment.

Something tells me ya can't really calculate this stuff exactly and ya just have to start building, turn on your fans, monitor your temps and adjust accordingly. Unfortunately, there may be some wasted materials.

 

[Norkali]

Yep, there are discrepancies - some call for double the area, while other figures call for just 10% more area. 10% is the minimum and double is overkill for sure. Notice that he says 'up to' double, in order to make up for losses (I figure this is where you account for bends and static pressure - and about where actual hands-on building and trial and error will come into play)

As for the 6.6'' and 7.2'' intakes - you followed me correctly. Just remember to make sure that the flower intake is at least 10% bigger than the exhaust, and accordingly - the veg intake at least 10% larger than the calculated flower intake.

Hopefully there will be no wasted materials, but such is usually the life of a novice grow-room builder. You'll find a use for the left-over materials eventually, trust me.

I recommend staying away from the S&P's, the mixed-flow fans such as those have a harder time with static pressure if I remember correctly....yep they do. I was gonna go the same route you did, thinking I wanted stealth as priority #1, but am honestly glad I went with an inline centrifugal fan, as static pressure builds up QUICKLY in the vast majority of grow-rooms. I can tell an S&P wouldn't have cut it, and I was in a much more simple closet set-up than yours.

 

[stratagem]

I was gonna go the same route you did, thinking I wanted stealth as priority #1, but am honestly glad I went with an inline centrifugal fan, as static pressure builds up QUICKLY in the vast majority of grow-rooms. I can tell an S&P wouldn't have cut it, and I was in a much more simple closet set-up than yours.

Which particular fan do you have and how loud is it really? There seems to be some varying opinions about how "noisy" they really are. Are you using any methods to cover up or hide the noise? If I hang the fan directly above my tent on bungee cords and maybe put a box around it with some sort of deadening material (not sure what that would be yet) can I expect it to still be noticeable by anyone walking into the room past the closet or near it?

 

[stratagem]

Also, this isn't exactly on topic, but is aerating your water/nutes (for hand watering/feeding) with an aquarium pump and air stone really necessary? I add a pinch of ascorbic acid per gallon and let my water sit for at least 4 hours. My tap water has chloramine. I didn't test my city's water but while in another city, I used an aquarium chlorine tester which indicated the presence of chlorine then I added a pinch of ascorbic acid and retested which resulted in the absence of chlorine. I suspect it's working on my city's water as well. I might grab a cheap dye tester myself though to confirm.