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InvisibleGod
Yahweh

Registered: 09/26/08
Posts: 434
cab design
    #251548 - 07/19/09 10:44 PM (7 years, 4 months ago)

So I've been thinking a lot about how to design my perpetual harvest cab, and here's what I've come up with so far:


(Sorry if there's any confusion with all the numbers, I tried to color code to make things easier.  Blue arrows are airflow, numbered so you hopefully don't get lost.)

Total cab volume is about 80ft3.  The air will flow from the light into the electronics chamber through 6" ducting.  The carbon filter will be connected to the fan with the same.


I have a few places that I've started to get stuck, so hopefully some of you can help me.

1. I'd like the only fan to be the 160cfm at the end of the line, and for all intake to be passive, starting from the floor of the mom room, via the negative pressure in the cab.  Assuming the cab is airtight, can I rely on the physics of pressure?

2. I'd like to route air to parts of the cab that need it (around plant soil level) with PVC piping.  I could use a little help calculating how much cross-sectional area of piping I'll need.  If my fan is 6" in diameter (28.25"2 area), should I just use a combined area of ~28"2 of PVC for the intake?  I realize that the less area of pipe I use, the faster the air will have to travel through it.  I don't want to pummel my plants!  (Also, I know there'll be some drag in those pipes.  How to calculate/compensate?)

3. I can't decide what to do with the mom/clone area.  I could use both chambers for moms, I guess, or use the upper chamber for housing nutrients, etc., but I think it'd be put to best use as a clone chamber.  If so, can it afford to be smaller than the mom chamber, or should it be larger to accommodate clones' vegetative growth?  I've got 3.75' of height to work with.

4. Carbon filters.  I know how they work, and how to make one, but how big should they be?  I figure one that's about a foot long and 6-8" wide should be fine for this size cab.  Thoughts?

5. My fan has issues.  It runs fine, but when it's on its side (or in any position other than blowing air vertically), it makes some pretty obnoxious rattling noises and the fan slows considerably.  I want to run it in a vertical position, so this may not be a problem, but I wanted some others' thoughts on the subject.  Also, some suggestions on how to dampen fan vibrations would be great.

I may post follow-up questions as I think of them.  Please don't hesitate to critique any parts of the cab that I didn't ask about.  Thanks!


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InvisibleGod
Yahweh

Registered: 09/26/08
Posts: 434
Re: cab design [Re: God]
    #251824 - 07/20/09 01:14 PM (7 years, 4 months ago)

I know it's a bit long, but does anyone have any ideas/questions/concerns?


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Offline81renaissance
Coachella '13 KKOTY
Male


Registered: 04/20/08
Posts: 4,181
Loc: State of Mind Flag
Last seen: 4 months, 27 days
Trusted Cultivator
Re: cab design [Re: God]
    #251899 - 07/20/09 02:34 PM (7 years, 4 months ago)

1. Yes...there's a reason why they're called laws of physics. :smirk:
2. Use the KISS rule and put an oscillating fan in there. If you don't want to do that, post again and I'll link you to a formula to calculate for ventilation
3. As long as you're aware that you'll need to make that "clone chamber" completely lightproof and that it will need it's own light, then you're fine.  Same is true of the mom box.  I would actually build a separate space just to cut down on heat and also for the sake of convenience ("can I get into my clone box right now? No, my plants in the flower chamber are on their dark cycle...etc.")
4. I don't know...I buy filters.
5. If it isn't a problem don't worry about it. If it is, either buy a new fan or take it to a service tech who can fix it.  That seems pretty basic.  As far as dampening the noise use the search function or browse the grow journals and cult forums...there have been several posts about that.


--------------------
"So it goes."
-Kurt Vonnegut


BlueBerry_Swisher said:I want French fries. No, I want a penis French. Thank you. I'm so excited. I can not contain myself. Now I eat chocolate. It is so good. I'm trying to rub it all over myself. And then lick. Now I need a hot shower. The end.


Edited by 81renaissance (07/20/09 08:03 PM)


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Invisiblejwes420
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Registered: 05/13/09
Posts: 258
Loc: NE Great Lake Region
Re: cab design [Re: 81renaissance]
    #251912 - 07/20/09 03:26 PM (7 years, 4 months ago)

#5: Sounds like the bearing in your fan is blown. Get a new fan.


--------------------
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.........."And You Will Come to Find, that WE are ALL, ONE MIND.....
.....Capable of ALL that's IMAGINED, and ALL That's CONCIEVABLE.....


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InvisibleGod
Yahweh

Registered: 09/26/08
Posts: 434
Re: cab design [Re: 81renaissance]
    #252156 - 07/21/09 01:28 AM (7 years, 4 months ago)

1. I guess what I meant was, am I understanding physics properly? I didn't want to set out to do the impossible.
2. An oscillating fan was what I first considered, but I disregarded it due to space limitations and the extra noise it will contribute. I'd like for my cab to be as close to silent as possible, as it would be odd for whirring noises to be coming from my "equipment cabinet." :wink: Perhaps a small, quiet fan is the best option. I'll do more research, but would definitely appreciate the linkage. I have all the equipment and most of the know-how necessary to construct the PVC system, but I get so lost when trying to wade through physics beyond my normal scope. I feel like I could use PV=nRT, but with all the variability, I was hoping for something more specific.
3. A very good point that I hadn't given enough thought to. After doing so, I think I will leave the design as it is, with the exception of using two seperate doors: one covering just the flower chamber, the other covering the moms, clones, and electronics.
4. Out of curiosity, why do you buy filters? For simplicity and professional reliability, I assume. I'm tight on cash, so building whatever I can is my best option.
5. Again with my lack of funds, I was wondering if anyone had any ideas on what could be wrong and how I could fix it myself. If that's not reasonable, I'll have to buy another, I guess. This fan has never been used, I got it from HTG Supply when purchasing my light. Not sure that it's the best quality; GrowBright?


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Offline81renaissance
Coachella '13 KKOTY
Male


Registered: 04/20/08
Posts: 4,181
Loc: State of Mind Flag
Last seen: 4 months, 27 days
Trusted Cultivator
Re: cab design [Re: God]
    #252160 - 07/21/09 01:40 AM (7 years, 4 months ago)

Some info here regarding airflow in cabs...I use a passive flow system and I think that in your case you won't have a problem...you aren't gonna lose HALF of your cfm to drag.  You can apply this info to the PVC flow system as well, just calculate the total volume of the pvc you're using, multiply by a reasonable drag coefficient (maybe .15 tops) and get the closest fan you can find.


--------------------
"So it goes."
-Kurt Vonnegut


BlueBerry_Swisher said:I want French fries. No, I want a penis French. Thank you. I'm so excited. I can not contain myself. Now I eat chocolate. It is so good. I'm trying to rub it all over myself. And then lick. Now I need a hot shower. The end.


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InvisibleGod
Yahweh

Registered: 09/26/08
Posts: 434
Re: cab design [Re: 81renaissance]
    #252389 - 07/21/09 03:06 PM (7 years, 4 months ago)

There's some great information in there, thank you!  I'm considering just turning most of the floor of the Mom chamber into an baffled intake (no PVC, to save space). Same with the Clone chamber, only using PVC to carry air from clones to Flower chamber. But I'm concerned about fresh air just hugging the walls and not touching the Moms and clones. I know I can disperse it with oscillating fans, but I'm trying to save space and avoid unnecessary noise. Would sticking with my slightly bulky PVC idea be more efficient, or do you have any other ideas? Thanks for all your help.


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Offline81renaissance
Coachella '13 KKOTY
Male


Registered: 04/20/08
Posts: 4,181
Loc: State of Mind Flag
Last seen: 4 months, 27 days
Trusted Cultivator
Re: cab design [Re: God]
    #252617 - 07/21/09 09:29 PM (7 years, 4 months ago)

Oh I've always got more advice! :grin: :wink:
The PVC thing would work I think (I'm actually toying with the idea myself thanks to you), but whether you use it or just baffle the passive intake from the floor up, just vary the direction that each hole faces so as to create your own "oscillating" effect.


--------------------
"So it goes."
-Kurt Vonnegut


BlueBerry_Swisher said:I want French fries. No, I want a penis French. Thank you. I'm so excited. I can not contain myself. Now I eat chocolate. It is so good. I'm trying to rub it all over myself. And then lick. Now I need a hot shower. The end.


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InvisibleGod
Yahweh

Registered: 09/26/08
Posts: 434
Re: cab design [Re: 81renaissance]
    #252822 - 07/22/09 04:08 PM (7 years, 4 months ago)

Good to know that I've inspired some thought!  I've been thinking about it a lot, and have finally come up with this idea:



This is two side views of the Mom and Clone chambers.  The left half is the left wall of the Mom (bottom) and Clone (top) chambers, and the right half is the right wall of the same.  Air flows in through the bottom left of the Mom chamber via six 3" PVC pipes (ID=3.042", OD=3.5"--> that's 43.61"2), exits those pipes through (at least) 222, 0.5" holes (that's 43.59"2) drilled all over for the "oscillating" effect that you mentioned (I didn't draw them all, obviously).  From there, air flows across the Mom chamber to an identical setup on the right wall, where it then flows up through the Mom ceiling/Clone floor, flows out via the same concept as before, and into six more 3" PVC pipes, which flow into the Flower chamber and distribute air evenly in a way that I'm still working out the kinks in, but will post more about soon.  Whew!

For reference's sake, both chambers are 48" deep by 17-20" wide (haven't decided exactly, but it's to make up for the extra 7" of pipe inside the chamber) by 27" (Mom) and 18" (Clone) high.  I may end up altering this design to minimize extra pipe thickness by using more, smaller PVC.  I haven't decided if it's worth it, since each decrease in size increases the amount of PVC needed exponentially.

I think this will work better than any of my previous ideas, as it will (hopefully) achieve laminar flow across all of the plants in all chambers, eliminating the need for potentially noisy fans.

Thoughts?


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InvisibleGod
Yahweh

Registered: 09/26/08
Posts: 434
Re: cab design [Re: God]
    #253093 - 07/23/09 04:04 AM (7 years, 4 months ago)

Also, I started another thread on the subject of perpetual harvest, if you're into that sort of thing...


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