How exactly does cubic feet per minute work ?

Saerimmner said:

Actually its the other way round you want the air in the room exchanged 2-3 times per minute, not once every 2-3 minutes so you need a higher CFM fan that the cubic capacity of your room i.e. if your room is say 7 cubic metres then you want to exchange over 21 cubic metres of air per minute

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So if you have an 8x12 room 8 foot tall you're saying you need to use 2304 cubic feet of air circulation, which means that if you're using a 6" inline fan that does 400 CFM attached to a carbon filter which cuts the CFM by at least 1/4th you'd need 7 approximately 1400 dollars in inline fans and carbon filters just to properly scrub you're room....lol

lol 2-3 times a min is just crazy.... wont leave plants time to think

This is where my knowledge of grow room design stems from.


http://urbangardenmagazine.com/2010/07/planning-your-grow/



Enjoy the read.



J

jondamon said:

This is where my knowledge of grow room design stems from.


http://urbangardenmagazine.com/2010/07/planning-your-grow/



Enjoy the read.



J

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It states 1x per minute, not 3x per minute

Actually it mentions this.


‘Summer sized fans’ are also not always the answer to a warm indoor garden. There comes a point where it doesn’t matter how much air your extracting, if your incoming air is warm your room will stay warm. If you can’t keep the heat down and you’re changing the air in your garden more than three times a minute, you need to consider installing air conditioning or using air-cooled or water-cooled grow lights.


If you are exceeding 3x per minute consider using AC or air cooled reflectors.


I hate it when people quote something without reading the whole fucking thing.

Like I said in an earlier post 3x is the max. I work on 1x per minute then allow for everything else.



J

skunky33 said:

So if you have an 8x12 room 8 foot tall you're saying you need to use 2304 cubic feet of air circulation, which means that if you're using a 6" inline fan that does 400 CFM attached to a carbon filter which cuts the CFM by at least 1/4th you'd need 7 approximately 1400 dollars in inline fans and carbon filters just to properly scrub you're room....lol

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lol i dont even remember that post/this thread, musta been well fucked up when i posted it lol even i can see its beyond wrong lmao

Trying to srub the air 3 times a minute in a room of any size at all is a waste of energy and equipment and is totally not needed, at least in growing. Once every few minutes is all that is needed, anymore, is just more and nothing else, no improvement in air quality to be measured.

Peace

Asmallvoice

ASMALLVOICE said:

Trying to srub the air 3 times a minute in a room of any size at all is a waste of energy and equipment and is totally not needed, at least in growing. Once every few minutes is all that is needed, anymore, is just more and nothing else, no improvement in air quality to be measured.

Peace

Asmallvoice

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I agree it is a waste. However the max a room can be exhausted should be 3x. I'm not saying this is the norm it is the MAX if you find yourself toying with 3x then its time to consider AC and air cooling.

Personally if I didn't start at 1x then add all the restriction %'s then my room would not be cool enough as I don't have AC seeing as I live in the UK.

If you have house AC that can be used then 1x or less maybe sufficient.

Again though the link I posted to talks about basing your fan on the actual growing area NOT the room size.



J

Grow4tho187 said:

I'm using a 2000 cfm carbon filter and a 8'' vortex in-line as air in-take and 8'' vortex sucking air out the filter ( which is almost bigger then me ) through 4 cooled reflectors and out side of a 8x8 tent ! Now I know its way over kill lol I put a speed control on in-take to have a negative pressure , so no leaks ! . Im starting a new show with a 10x10x6.5 tent , Not the gear that is missing just the full knowledge of how to calculate cfm's thx for the help

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those 8" vortex are sweet.

Jesus fucking christ people. How do you all ever manage to get through a day of life without electrocuting yourself or running yourself over with your own car?

Jondamon (fucking stupid name BTW) you are talking about somethign entirely different than the OP. His question was about what CFM for scrubbing a room, not how much CFM to cool a room with outside air.

A couple guidlines that have not been taken form a single source, but have come from multiple sources and designing, building and operating multiple grow room.

SCRUBBING: all the air every 3 minutes. In high humidity areas, better spec out every 2 minutes. So your CFM on your fan should be 1/3 or 1/2 of the room volume.

FLOW FOR AIRCOOLING HOODS: 6" for 5 hoods or less in a row, 8" for more than that in a row. A single cheap 6" inline will effectively cool 4 hoods. Anything over 5 hoods in a row, you would do well to put a booster fan on the inlet. After about 7 hoods, the last 2-3 hoods in the chain are not gettign cooled at all really.

AIRFLOW FOR COOLING: this is WAY to complex for discussion here as there are a vast multitiude of variables that come into play. inlet size, outlet size, locations of inlets and outlets, ari flow pattern in the room, total air cirulcation, outside temperature, how big your plants are, bare bulb vs non bare bulb. At any rate, for most temperate climates your starting point CFM is indeed the volume of your room. You should have that CFM on BOTH the inlet and the outlet. having a passive outlet or inlet will really kill flow rates.

For a super small can like that I would just use a
Cheap ass Home Depot inline booster fan. The 4" has a real world cfl in the range of 150 or so.

you have a room of 700 cubic feet, you want to change the air lets say every 3 minutes. You would need 20 air changes an hour. the formula for this is cfm x 60 (minutes in an hour) divide by the cubic feet of the room. CFM cubic feet per minute. At 225 cfm. 225 x 60 = 13500 cubic feet per hour. divided by your cubic feet. 13500 / 700 = 19.29 air exchanges per hour. You will need about 225 cfm fan with no restrictions. that is at a .1 static pressure from your exhaust system.

legallyflying said:

I think that the general rule of thumb is that for carbon filtering, you want to scrub the whole room in under 5 minutes, preferably 3. So what this means is that the entire volume of your room passes through the filter in 3 minutes. Therefore, the CFM rating of your fan should be 1/3 the volume of your room. Your filter should be sized according to manufactures specifications. Don't put a lare filter on a small fan or vs versa.

If your scrubbing and your in a tightly sealed room, you can go with a lower CFM. However, pleae note that te efficiency of your carbon depends on the humidity. When you get above 60% it falls off rapidly. So don't go too low.
Cheers
LF

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Bingo. 1/3 to 1/5 the room volume has been my rule of thumb. I have a 335 cfm fan servicing an appx. 900-cubic-foot room. What I've done though is use a variable transformer to dial the fan waaay back, and I'm probably drawing less than 50cfm through it. That one fan cools my light and filters the tent's air ... and it all works great so far. cn

On the opposite side of the spectrum I just bought and built an enclosure for an 1800cfm blower that is hooked to a 18" by 40" carbon filter. . Man that thing moves some air when I put it on high!