CFM correct?

[greenduck]

what's the best CFM's needed in my 1500 cubic foot room to clean the air? should it be cleaned every 3,5,or 10 minutes? please help thanks.

I need to purchase a new carbon filter for my blower to scrub the room. i have two options. a 6inch and an 8 inch. i havent looked at the CFM's on either vortex blower but im curious to know if my calculation is correct and if you can let me know what to use to get the best filtration. my goals are to filter the smell as well as anything else and im guess with one you get the other?

to know the cfm's needed:
my room volume is 1500 cubic feet. if i wanted to clean the air in 5 minutes. thats 1500/min's.= cfm. or volume / mins. =cfm.

this correct?? so
1500ft cubed/5mins =300 cfms.

again, lets say i use a bigger filter and blower with higher cfms. id get
1500/3 mins= 500 cfm. so 500 cfm's to clean the entire room in 3 mins.

also, does the white fiberous scrubber that surrounds the carbon filter restrict the fan? if so, how do i calculate that in the mix. thanks.

-GD

 

[Bennyweed1]

Your formula is off.

Basically it should look like this:

Room cubic feet X the amount of exchanges in 1 hour.

In your case 2 exchanges per minute is 120 exchanges in 1 hour (multiple amount of desired exchanges by 1 hour).

1500cuft X 120 per hour = 180,000 cuft of hourly volume

180,000cuft / 60 minutes = 3000 cfm needed.

Thats a massive amount of space your growing in...

 

[Hydrolized]

I've never done exchanges per hour, always minutes per exchange, as OP asked. Usually my rooms are 1 exchange every 5 minutes and that's never been a problem so 300CFM will work fine. The carbon in the filter will do most of the restricting, that foam pre filter will add negligible static pressure....1500 Cubic Feet is about a 10' x 18' x 8' room...not really that massive at all.

Keep in mind that whatever CFM you decide, you will need to pick a fan that will move that CFM at the static pressure of your setup. Most carbon filters create about .75" W.C. SP, which will make most fans move about half the "rated" CFM listed on the box @ 0" W.C. Any fan worth the money will have a chart showing the CFM at various static pressures, so if you pick 300CFM, just go on the chart and find .75" and find which fan will move 300CFM etc.

 

[greenduck]

@bw. it's 1500 CUBIC FEET. i think your equation is off but thanks for the reply.

@hydrolized. perfect explanation and im glad i was close. im a bit confused on the W.C. thing but ill look up each of my blowers and see what the rating is and the. i also look at the carbon filter W.C. i guess you are saying. if i want 300 CFM, maybe the CFM's on my blower should be around 450-550 to create the needed 300cfm movement.

 

[Bennyweed1]

My bad, I always shot for 2 exchanges per minute. Didnt recognize you meant 1 exchange ever 3,5, or 10 mins.

must be using sealed hoods or have a/c? Both?

 

[greenduck]

here is what i have.

8 inch Elicent - 640cfms on 250 watts.
and
8 inch Vortex- 747 cfms on 260 watts.

would like the 8x24 inch Phresh Filter rated to a max of 750cfm's so looks like i can use either but i cant find if either have .75" W.C. static pressure. if they do, then it would just do this.
.75 x 747cfm's (vortex 8inch) = 560 cfm's output with the filter??

guess ill just go with the Vortex cause it starts at 747cfm's.

let me know, thanks

 

[greenduck]

no worries bw. 2 exchanges perminute would be a lot unless you have a micro grow?

i have a split a/c unit, its ice cold!! no cooling my fans. i like the closed system of my room. no air leaves and no bugs enter... or we hope for lol.

 

[SacredBreh]

Full room exchanges every 30sec?

Full room exchanges every 30sec?

That is is extreme over kill unless you have like a crazy heat problem and then over all design is the issue.

Peace

 

[greenduck]

and, it looks like i only need around 300-400 cfm's so i may just use my 6 inch fan because i think it's some where around 440cfm's

 

[greenduck]

scaredbreh, i think he mean's a micro grow. but we'll see

 

[Bennyweed1]

scaredbreh, i think he mean's a micro grow. but we'll see

Oh sorry peeps. I run 2000w vertical bare bulbs in 224cuft and it takes twice a min air exch. to get temps in check without A/C. I forget the game is different with hoods because I haven't grown with them in so long.

 

[SacredBreh]

Here is a calculation method that is fairly simple.....

Here is a calculation method that is fairly simple.....

Hope this helps out. One thing to consider... A fan running at its max will make a huge amount of noise compared to running at say 50% power so I always go oversized on the fan and the ducting and then put speed control on it. Plus, with humidity, temp, and other conditional changes over the year and seasons, you will be able to adjust for them.

Also, I have tried numerous different types of fans and by far the best are Vortex..... little more costly but worth every penny.

http://www.bghydro.com/BGH/static/articles/0606_vent.asp
Ventilation Explained
Part 1 - Ventilating your growing area
Correctly ventilating your growing area is a vital part of greenhouse/grow room design. Adequate ventilation in the grow room is important for a number of reasons – temperature, humidity, disease and odor control, and fresh/stale air exchange. The calculations that are used to correctly design a ventilation system can be quite complex and require numerous known variables. The purpose of this article is to simplify these calculations while helping you to better understand grow room ventilation.


How to size your exhaust fan

There are many calculations on the web for sizing a fan for ventilating grow rooms; however, what these calculations fail to take into consideration is the friction loss on carbon filters, increased temperatures from HID lights and CO2, etc. The following calculation can be used as a guide for sizing an exhaust fan for a growing area (keep in mind that this calculation will give you the lowest required CFM required to ventilate the grow room):

Step 1 – Room Volume
First the volume of the room needs to be calculated. To calculate multiply length x width x height of growing area e.g. A room that is 8' x 8' x 8' will have a volume of 512 cubic feet.

Step 2 – CFM Required
The fan should be able to adequately exchange the air in a grow room once every three minutes. Therefore, 512 cubic feet/3 minutes = 171 cfm. This will be the absolute minimum cfm for exchanging the air in a grow room.

Step 3 – Additional factors


Unfortunately, the minimum cfm needed to ventilate a grow room is never quite that simple. Once the grower has calculated the minimum cfm required for their grow room the following additional factors need to be considered:

1. Number of HID lights – add 5% per air cooled light or 10-15% per non-air cooled light. CO2 – add 5% for rooms with CO2 enrichment
   Filters – if a carbon filter is to be used with the exhaust system then add 20%
   
2. Ambient temperature – for hot climates (such as Southern California) add 25%, for hot and humid climates (such as Florida) add up to 40%.

Example 1:

In our 8’ x 8’ room we have 2 x 1000w air cooled lights, and we plan to use a carbon filter. We also plan to use CO2 in this room. The ambient temperature is 90°F, however, we will be using air from another room that is air-conditioned.

Minimum Required CFM to ventilate room:

(CFM required for room – step 2) + (CFM required for room – step 2 x 10% (2 air cooled lights)) + (CFM required for room – step 2 x 5% (CO2)) + (CFM required for room – step 2 x 20% (Carbon Filter)) + (Ambient Temperature 0 (Air coming from air-conditioned room)).

= (171cfm) + (171cfm x 10%) +
(171cfm x 5%) + (171cfm x 20%) + ( 0 )


= 231cfm – this is the absolute minimum cfm required to ventilate your room.


The next step would be to match the closest fan to this CFM. As we are using a carbon filter we will need to match the fan with the filter so that the fan that will neatly fit onto the filter. The filter that we will use is a Dutch Breeze Carbon Filter - DFS4. The DFS4 has a 6" flange. Our options for 6" fans are as follows:

- Eco Plus 6” – 440cfm
- Fantech 6” – 252cfm
- Fantech 6” XL – 392cfm
- Elicient 150B – 309cfm



The DFS4 filter has a cfm rating of 255-309, so the fan that we will choose for our room will be the Elicient 6” fan. This will be an ideal fan for this room and carbon filter, since the extra cfm will help compensate for the small amount of ducting we may have to run.

If only step one and two was used (the calculation that is most commonly displayed on garden websites) then the grower would have chosen a 4” fan and a 4” carbon filter; the grower would have soon found out that this fan and carbon filter would have been inadequate for their grow room.



Example 2:

If all the variables are kept the same and we changed the room size from 8’ x 8’ to a 12’ x 12’ then the minimum required CFM would be 519 cfm, thus the fan would be Fantech 8” XL, Elicient 8” or EcoPlus 8” and the DFS5 or DFS6 Dutch Breeze carbon filter.


The Really Simple Method:
If you want to keep things really simple, just remember that you want to replace the air in your grow room every one to three minutes. If you're in a hot area, exchange it every minute; if you're in a cooler area, you can take up to three minutes.

Peace

 

[greenduck]

thanks for the details scaredbreh. its not stated above but you humid and warm air increases molecule size those your calculating for this which would increase the CFM's because of the weight slowing down the air flow??

ALSO, im not ventilating my air out of the room. so, im just recirculating through a carbon filter...different story, right? maybe not since you are accounting for variable. sorry, im a few beers deep trying to understand this all. lol.

the above details just say "10-15% per non air cooled light" what if im using 11, 600 watt bulbs verse 11, 1000 watt bulbs?

 

[greenduck]

indeed benny, i had a feeling you were in a small area with non a/c. good luck with that, atleast your bill is probably really low

 

[SacredBreh]

yes different story.......

yes different story.......

How are you getting new air in or are you running a sealed CO2 room. If not sealed CO2 room you have to have new air.

Peace

 

[Scrappy-doo]

What happens if you don't have a big enough cfm fan/filter? Aside from heat. That's not an issue in my situation.

 

[greenduck]

its a sealed co2 room with a split a/c. im pretty sure if i do atleast 300cfm's that will be fine. 500 would be plenty. your thoughts? im really only scrubbing the air for smell to no piss off the neighbors...and it cleans the airborne microbes.

 

[greenduck]

scrappy, you in a sealed room or venting new air? if your in a sealed room, you just arent cleaning the air as often. with the vented room there are issues of heat and humidity build up unless you have a dehumidifier. that's all i know lol