Capn Style Perpetual Grow Room Question

[blitzman734]

Hey everyone,
I'm looking to build out capn style perpetual grow room in my garage and I'm curious to get some feedback on my layout but most importantly on how I should ventilate it.

I chose to separate the flower rooms so I could air dry for the 4-5 days during harvest right inside the room. This would obviously delay the perpetual nature of it a bit lol but I can at least ensure proper climate / humidity and darkness with this type of layout.

I'm in michigan so my garage can get a little chilly in the winter time, ive already insulated the door with R7 rigid foam board and applied weather stripping to the sides and top to keep the drafts down as well as placing some foam in between the tracks a bit to keep the wind from pushing it open to much. I dont want to permanently seal it but I dont park any vehicles inside of it so there isnt the day to day need to open it.

My ventilation questions are where should I place the carbon filter or filters. As well as how large should my filtered passive air intakes be and should the flower rooms have there own or should I utilize the veg room as a complete lung room and place the carbon filter and intake only within it and place light proof vents between the veg and flower rooms with the negative pressure sucking into veg and out a carbon filter. There are too many options and without prior experience i'm curious how this great community would do it. I've attached a image below of the layout I came up with.

Each of these rooms would be roughly 246 cubic feet.

I know this was a lot to ask and had a lot of information and appreciate your input.

 

[blitzman734]

Im also toying with the idea of combining the two flower rooms and just having like a mylar curtain to block the direct light from the drying bud

 

[scruffy420]

Well, to start off, are these rooms physically separated by walls, or are they just partitioned into different sections? If the rooms are basically air tight from the outside, it makes it easier to ventilate each room individually. If they are open air, it would probably be easier to just run a system for the garage as a whole, essentially. I've heard "rules of thumb" say that you want to move the volume of your room between once every minute, to once every five minutes. That doesn't seem like a lot, but it is a huge difference. If you're going to be running 2 4x4s for flower, and drying in there, you're gonna want some serious fire power. So, just for the sake of showing you how to do it so that you can extrapolate this to how you would prefer to do it, I'm going to assume that you just want to ventilate the three rooms you've shown here.

Take the volume of all three rooms:

246ft^3 x 3 = 738ft^3

Giving a range of venting fresh air between once every 1 to 5 minutes:

738 CFM (once per minute)

or 738 ft^3 / 5= 147.6 CFM

Now, this gives you the range of 147.6-738 CFM. Keep in mind that this is ONLY to supply fresh air to the plants. That doesn't really take into account the heat given off by your lights. If you're using HID lights, you'll probably want to add some (perhaps, around 25%). Also, if smell is an issue, you'll want carbon filters. You have a decently large setup, so depending on how air tight this place is, you might want two filters. Add 25% for carbon filters. I'll give the worst-case scenario numbers:

147.6 CFM x 1.5 (25% for both cases listed above) = 221.4 CFM
738 CFM x 1.5 = 1107 CFM

Somewhere in this range is where you'll want to be. As long as your temps are okay, I've always read that more ventilation is always better. More air = more CO2 = more green stuff. Therefore, it wouldn't be a bad idea to go with the higher side of the numbers here. I definitely wouldn't do the 221 CFM. 221 CFM, in this case, is a MINIMUM.

Now, we have your required air flow. Let's talk about setup. I like to filter my incoming air. Keep nasty crap out of the garden. Also, if you ever start to want to breed, HEPA filters will take the pollen out of the air for you. So, what my thoughts on the topic are:
-Run two fans with separate filters
-Place both in your veg room, with passive intakes in each of the flower rooms.

The reason I say this is that, in the event that one fan fails, the other can still operate and provide negative pressure to both flower rooms and keep air moving. When in doubt, fail conservatively.

So, given the setup I've suggested, we need to talk about passive intakes. I would say go with some HEPA filters on your intakes. Nothing too fancy, just your regular filters that you put in household ventilation systems. You can get these in a large range of sizes and qualities, so pick what works best for you, but I'll just assume the standard size of 20"x20". We'll assume that you'll run two 8" fans, each pulling 710 CFM, max (speed controllers will let you turn this down to, say, 500 CFM each). So. A total flow of 1420 CFM, minus losses due to the carbon filters and other various things that cause pressure drops, probably does put you around about 1000 CFM. We'll use 1000 CFM for ease of math. The maximum face velocity of most of the HEPA filters is 500 FPM (ft per minute). We'll be pulling 1000 CFM through them. I'd say one per flower room will do nicely. We assume that both flower rooms, and therefore the pressure drops that occur within them, are identical and equal. This means that we can calculate based on only one room, and using 50% of the total air flow. Math time:

20"x20" = 400 sq in. (each filter)
400 sq in / 144 sq in (1 sq ft = 144 sq in) = 2.8 sq ft of filter area
Flow through the filter = 500 CFM (total flow/2)

500 ft^3 / 2.8sqft = 178.6 FPM

178.6 FPM is less than the maximum velocity that the filter can handle, so that checks out. The filter is more than large enough to supply all of the flow for your room, so that checks out. Your fans are pulling enough flow to ventilate your room, so that checks out, and you simply have to match your carbon filter to your fan. I suggest running 2 of the same fan/carbon filter setups. As a side note, you can reduce the pressure drop that occurs across your carbon filters by buying larger filters, (your diameter must match your fan still, but the lengths of different filters vary) which will help you maintain higher flow through your ventilation system. I'll include some links to items that may be of interest:

Fan - Amazon - Hyper Fan 8" 710 CFM Inline With Speed Controller - Hydroponics Medicinal Grow Ventilation

HEPA filters (notice that this is a pack of 6, and also the highest quality filters. You can definitely downgrade and get some cheaper ones, it won't affect a whole lot.) - Amazon: US Home Filter SC80-20X20X1-6 MERV 13 Pleated Air Filter

Anyway, that's how I would do it. Two fans in parallel, pulling in veg, with passive intakes in flowering/drying rooms. Putting a fan in each flower room means that if one fails, the other won't ventilate the room with no fan. I like redundancy, for protection. Also, if your lights are HID, you may think about running them on their own ventilation fans or systems. It keeps the temps in the room down a lot if you ventilate the hood itself. I think most hoods are 6" ducts, but with a few cheap parts, you could run your light hoods directly off of your 8" exhaust fans (all you would really need is an 8" to 6" reducer, available at home depot, or other hardware stores). If your lights are LEDs, you needn't really worry about it. I hope this helped, and didn't make you want to kill me, because this is a lonnnnnggggg post. I wish you all the luck, and happy growing!

 

[Weaselcracker]

Just my 2c. I have an 8' x8' flowering room. In that room two hps lights run, each covering an area about 3.5' x 4' and producing about a pound per harvest for each light. I made a drying box out of a mini fridge (about 2' square and 3' high) which sits in the corner of the flowering room. With staggered harvests meaning I never have to harvest more than three plants on any given week- I've never needed more space than that little fridge to dry my buds in. It would be nice to have a dedicated room for drying, but it's not really necessary to have anywhere near that much space, and would tie up your whole room when you're drying.