Calling SpaceNeedle. HVAC question.

I was told to search you out because my question wasn't getting answered in my thread here:

http://boards.cannabis.com/indoor-gr...fans-fans.html

Ultimately my question boils down to this:

(from the thread) I guess I just wanted to know where in an 18 foot run of duct that has a light in the middle of the run, would you place a 275 cfm and a 175 cfm fan to get the best cooling possible. Forget all that other stuff, if someone could just answer that it would be great.

If you could take a look at my problem and dispense some of your expert knowledge and opinion, I would appreciate it very much.

hmmm, well, my duct fan specifically instructs to use it ONLY for 'pushing' cool air, and not 'pulling' hot air into the fan motor ... but, since it's intended use is for assisting furnace air to be moved, I can't see the heat bothering the motor (but, I'm a truckdriver, not a HVAC guy :D) ... not knowing shit about HVAC, I would think you would want the 175cfm at the Inlet, and the 275cfm at the Outlet ... I'm thinking if that was reversed, the first fan would be fighting against some back-pressure, when it encounters the slower fan ... well, that's the theory for exhaust pipes, anyway :D

Ok, I've read your thread. Your 6" inline 267 cfm fan should suffice for what you want to accomplish. You did however state that you are using 4" lines. Well, I am saying you should use 6" a line. I knew you weren't gonna like that. If you cannot use 6" lines throughout, can you do the majority of your line 6"? I don't know what kind of pipe you are using. If you're using coiled flexible dryer vent line, get rid of it. You need to make the line as 'smooth' as you can to get the best possible airflow. The flexible lines, especially for a long run such as yours is going to hinder airflow due to the ribs (coils) inside where the air is supposed to flow. One of the answers you had on your thread is to have as few turns and bends as possible. If you do have a bend let it be as gentle as possible. The smoother your pipe is on the inside, the better your airflow. That's why an airplane has a smooth surface....and an airplane wing without rivets protruding on the surface will fly better/faster.

Going back to the size of your line. You should be using 6" warm air pipe. If there is an area where this is impossible, then use the 4" where you have to, then using a 6"to 4" reducer, continue with the 6". Please be aware however, whenever you do, there is a lot more pressure in the area of the 4", and it will produce turbulence which is not good for airflow -- similarily if you run a 90 degree elbow.... your are hindering airflow again.
Your fan should PUSH, not pull.
I have the same fan you have, using 6" lines (mainly 6" warm air pipe) and only using flexible line for maybe 2 ft on each of THREE 1000 watts lights, and I have total of about 20 feet from start to finish.....no problem.

You haven't mentioned anything about the internal ventilation of your room. oh, yea, you're using CO2.... that could be another problem without A/C . No matter what size fan you have to get rid of the heat from under the lights, a 600 watt bulb puts out 2000 btu's of heat, you will never get 100% of those btu's removed with the fan. After your light has been on for a couple of hours, touch your hood. I'll bet it's hotter than the ambient air inside your room. Eventually that will heat up your room just as if you have a frying pan heating up in there.
SpaceNeedle

What a load of info. And how unusual... It all makes sense.

I can't thank you enough for your help. I see that the image reaper agrees with you and Zandor about the fan pushing air over the light. That's good enough for me. I will make sure that happens.

I hereby vow to do everything whithin my power to:

1) Replace coiled line with real ducting whenever possible.
2) Take out as many bends as possible.
3) Make any bends as gentle as possible.
4) Use 6" line whenever possible.
5) Make the run of ducting as short as possible.

A lot of possiblities, and a lot more work for me ahead. The above, with my new larger fan, jut might do the trick.

I have the same fan you have, using 6" lines (mainly 6" warm air pipe) and only using flexible line for maybe 2 ft on each of THREE 1000 watts lights, and I have total of about 20 feet from start to finish.....no problem.

Good Lord! You are my hero. Is there a picture of this posted somewhere?

Again, thank you.

NO,no pics. Unless you still have a copy of overgrow....
You know I do regret not stating this: One of your comments in your orig thread was something like this "please don't tell me to use 6" when I have 4". Well right there you are cutting capacity by one third!
To be perfectly truthful, I should have said I had my 6" fan blowing thru 3 1000w lights. I don't anymore. I don't use CO2, and I have a charcoal filter, the largest available and a 12" fan runs that, which cleans the smelly warm air, cleans it and sends it outside. A while back I changed the ductwork whereby after the air is cleaned, part of it gets piped back thru the lights, and exhausts it back into the 'clean' side 12" exhaust. So now I have a 12" scrubber, and a total of 5 lights circulating all on the one 12" 1000cfm fan. Of course the air that goes thru the lights is already pre-heated to some extent, but it saves running 2 six inch fans. One fan was running 3 lights, the other was running 2.
SN

Quote:

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Originally Posted by SpaceNeedle

So now I have a 12" scrubber, and a total of 5 lights circulating all on the one 12" 1000cfm fan.

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OK, so you're still my hero.

Quote:

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Originally Posted by SpaceNeedle

Unless you still have a copy of overgrow....

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Wouldn't that be awsome. I wonder how many GB that would take up. I'll bet someone has it somewhere.

spaceneedle, i have a thread i could use your expertise on, in the closest section (title is- i couldn't help myself) sorry for hijackin

buy some kd (knock down) rigid duct from home depot, and remember every 90 degree elbow is like running 30 feet of straight duct. more 90s, more static pressure build up, fan has to work harder. would not recommend dryer vent at all. put damper (or fan controller)in supply so u can regulate negative pressure in room. if using co2 put backdraft damper in supply so no air escape through supply and electric damper on exhaust so it will open and shut when fan comes on and off. just my 2 cents, but don't trust me i have only been doing hvac for 11 years.

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Originally Posted by armbar

just my 2 cents, but don't trust me i have only been doing hvac for 11 years.

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For the most part, I trust everyone until they give me a reason not to.

And your advice sounds very reasonable. Thank you.