HVAC genius?

[growclean]

Ok, so I have got repeatedly lost during my HVAC plans, but am finally to the point of purchasing it all for the install.

I am trying to run an eventual 6 lights (4 1ks and 2 600s) on a closed system. I am buying all 8" hoods. To start we will have only one 600 and 2 1ks. We are going to be using 3 538 cmf fans (1 to start with). I went to an HVAC store today that usually only sells to installers and explained what we were doing. He admitted that the calculations were a little above him, but he ended up giving us a filtered 16x20 air return and proper reducers to take it down to 8" for intake and then just an 8" stove pipe type setup for the the exhaust.

I repeatedly tried to explain that I thought that we need a LARGER exhaust then we had for the intake. He didn't seem to think so.

1. Is that size of intake correct?
2. Is there a better method of exhaust?
3. Are we correct in thinking that we could have our first fan AFTER the first two lights and then essentially in line after every two after that? So pulling the air.


THANK YOU!!!

 

[PeteWeedSeed]

Its a tricky question, it all really depends on the setup and room setup. But a couple things to remember.
If your using one fan, It's always better to push air into the lights rather then pull so your not heating up the fan and burning it up faster. But if your dont care about that and dont replacing them you can pull the hot air.
for multiple fans, I have a 700cfm pulling from carbon filter and pushing over 2x 1kw into a master exhaust 20"x10"? something like that. there are 4 rows like this and they all tap into the master exhaust, which is much much bigger then the 8" intakes. Theres always an ozone gen before the first light, so the ozone has a long time to travel in to ducts cleaning the air. There is negative pressure in the room, the door takes some force to open and slams shut if you leave it open! my intake in the same size as exhaust, however it goes through a regular furnace filter first, so there is some slow down.

It's really hard to predict exactly, thats why I always go overkill. The dynamics of the room really change how much heat gets trapped when your over 5k power. So you will probably end up upgrading the fans or adding ducting paths, like I had too.

 

[BonsaiBud]

Throw enough high power, inline, axial fans in the works and that 8 inch stove pipe exhaust will be no problem. Add plenty of aluminum foil tape on every duct seam and get the expensive flex ducting from the hydro shop. You can get fish-tank thermal probes to put in the duct if you are worried about cooking your fan motor. If you get leaks around the glass of the hoods then get some super-low-profile, teardrop, white silicone door/window gasket from the hardware store.

I don't think you would have trouble pushing the air over the lights if you have enough fan power. Pull though a charcoal filter; push over lights; you will still have a room at neg pressure.

 

[freeganja]

I think pushing the air through the ducts would be a better idea than pulling the air through. How many lights are you going to use per fan? I dont have my book so I couldnt tell you the exact CFM you will need. As for the intake, it should be fine, but the more air flow you can get through your lights the better. You could use 1 fan per 2 lights pushing the air through and if you have no other ridiculously high ambient temperatures, you should be fine

 

[Lazyman]

Better to pull the air in from outside and blow it through the hoods back outside, that way the air never gets odorized by the smelly room, and you still can have a mostly airtight room you can run CO2 in. If you exhaust room air outside you can't run CO2 in most cases. In some grows you actually NEED the heat from open hoods and gas-fired CO2 generators, but it's often a mix of things to get your temps dialed in.

 

[Lazyman]

Oh yeah, and I usually figure 120-130 CFM per hood to keep em around 100*F output at the end.

 

[growclean]

Thanks again for all the replies! I think it sounds like we can make this set up work! We are drywalling today, so the duct work has a couple of days, but I will let you know how it turns out.