Fan Sizing

[DeJa]

Hey guys,

how big of a can fan will i need to cool a 150 cubic foot grow tent with 3 passive air ports [dark room]

I will be using 600 hps and 400 mh inside a growzilla hood over 6 plants

I will be running my fan at 40-80% capacity [controlled by variac]



can i get by using this can33 combo?
http://organic-hydroponicsupplies.t...2=680488228&CategoryID=45&Target=products.asp

or will i need something bigger like the can66
http://organic-hydroponicsupplies.t...2=680488228&CategoryID=45&Target=products.asp

 

[FreezerBoy]

fan-intake calculator

Ventilation 101

 

[Philosophelon]

You can probably get away with a Can 6HO and a Can 33, but you'll probably need to run it at full speed. If you have high intake temps and/or lots of ducting, you might want to get an 8" and use a speed control. You can always lower your fan speed, but you can't increase it (beyond full speed).

 

[DeJa]

You can probably get away with a Can 6HO and a Can 33, but you'll probably need to run it at full speed. If you have high intake temps and/or lots of ducting, you might want to get an 8" and use a speed control. You can always lower your fan speed, but you can't increase it (beyond full speed).

i cant use the 6HO with the 33 because the can33 has a max airflow of 200cfm


would this setup work at 60% speed?

http://organic-hydroponicsupplies.th...t=products.asp

 

[Philosophelon]

I couldn't get the link to work, so I'm just assuming it's a centrifugal blower.

Can you run it at 60%?
Yes, you just need a speed control.

Regarding the airflow of your fan, keep in mind that it will not pull its max rated airflow, due to static pressure added by your ducting, carbon filter, etc. For example, a Can 6HO is rated at 392 cfm with unrestricted airflow. But when operating under 1.25" W.G. (0.0452 P.S.I.), it only moves 179 cfm.

Here's another way to think about it that is (perhaps) more intuitive:

30 Degree bend -- reduces airflow by up to 20%
45 Degree bend -- reduces airflow by up to 30%
90 Degree bend -- reduces airflow by up to 60%

So even though the fan is rated at 392 cfm (for example), when installed it will move considerably less air than that, and you will probably have to run it at or near full speed.

 

[Vegan]

I couldn't get the link to work, so I'm just assuming it's a centrifugal blower.

Can you run it at 60%?
Yes, you just need a speed control.

Regarding the airflow of your fan, keep in mind that it will not pull its max rated airflow, due to static pressure added by your ducting, carbon filter, etc. For example, a Can 6HO is rated at 392 cfm with unrestricted airflow. But when operating under 1.25" W.G. (0.0452 P.S.I.), it only moves 179 cfm.

Here's another way to think about it that is (perhaps) more intuitive:

30 Degree bend -- reduces airflow by up to 20%
45 Degree bend -- reduces airflow by up to 30%
90 Degree bend -- reduces airflow by up to 60%

So even though the fan is rated at 392 cfm (for example), when installed it will move considerably less air than that, and you will probably have to run it at or near full speed.

I'm not so sure on those #'s
i have one of every bend listed above and my 4" is only running half speed and creates plenty of negative pressure in a walk in closet

to the OP
just get the can 66 that way you dont have to spend a small fortune on reducers and such

 

[DeJa]

sorry for the bad link guys

i really appreciate the help

heres a link to the can66 combo

http://organic-hydroponicsupplies.t...2=519340157&CategoryID=45&Target=products.asp

its an 8inch fan rated at 493 cfm

so i figure with the resistance of the carbon filter and ducting
i will be around 300-400 cfm

Im using my darkroom 150, 5'x5'x6'7"' around 160 cubic feet

i dont think i should count my intake because i wil be running a passive intake, 2-3 side screens and a 6" intake with a damper on it

i want the fan to be running 24/7 so that i dont have growroom smell leaking out my screened vents

if running the fan 24/7 will take too much power i can run it twelve and use passive air intakes with dampers on them, but i figure 24 hour air will be worth it for the health of my plants

i want the fan on 12 hours 70% while the lights are on
and 12 hours at 30-40% at lights off

i have yet to have someone accurately describe to me how i can have a variac control the fan and change between two different speeds without me having to go in every 12 hours and physically change the speed on the variac


thanks very much for the help guys

 

[Philosophelon]

I'm not so sure on those #'s
i have one of every bend listed above and my 4" is only running half speed and creates plenty of negative pressure in a walk in closet

First, all that a large amount of negative pressure means is that there is a large difference in pressure between your intake and exhaust, it has nothing to do with the amount of air moved.

Second, sorry about the scary percentages, I should probably clarify that a bit. The numbers for the % reduction of each bend are a conservative estimate of the worst-case scenario, e.g. pushing rather than pulling, a weak fan, flex ducting, narrow gauge ducting, etc., that's why I said "up to XX%" -- it's unlikely that you will lose the full percentage for every bend (or any of them, really). If you have the fan pulling, a powerful fan, larger diameter ducting, rigid/semi-rigid ducting, etc., you won't lose as much power. Again, not a particularly accurate way to measure resistance, but it's all I got if you don't have much HVAC knowledge.

If you want an accurate measurement of how much air will be moved, you have to know the exact amount of static pressure on the fan. This is actually kind of tricky and involves some math, as well as knowing the various drag coefficients of your materials, length of runs, bends, duct shape/size, etc. Then you look on the technical specs for the fan and see how much air it moves at that amount of pressure. Totally not worth the work unless you're setting up a pretty large grow, and if you are then you ain't here asking me HVAC questions.

As far as running your fan at different speeds during different times of the day is concerned, you've got me stumped. I've not run into any programmable rheostats with timers on them or anything (I live in the states), although I've never really looked. I can ask a couple of friends who still work at grow shops and see if they know of anything, but you might just be SOL.

 

[DeJa]

 

[Vegan]

First, all that a large amount of negative pressure means is that there is a large difference in pressure between your intake and exhaust, it has nothing to do with the amount of air moved.

Second, sorry about the scary percentages, I should probably clarify that a bit. The numbers for the % reduction of each bend are a conservative estimate of the worst-case scenario, e.g. pushing rather than pulling, a weak fan, flex ducting, narrow gauge ducting, etc., that's why I said "up to XX%" -- it's unlikely that you will lose the full percentage for every bend (or any of them, really). If you have the fan pulling, a powerful fan, larger diameter ducting, rigid/semi-rigid ducting, etc., you won't lose as much power. Again, not a particularly accurate way to measure resistance, but it's all I got if you don't have much HVAC knowledge.

If you want an accurate measurement of how much air will be moved, you have to know the exact amount of static pressure on the fan. This is actually kind of tricky and involves some math, as well as knowing the various drag coefficients of your materials, length of runs, bends, duct shape/size, etc. Then you look on the technical specs for the fan and see how much air it moves at that amount of pressure. Totally not worth the work unless you're setting up a pretty large grow, and if you are then you ain't here asking me HVAC questions.

As far as running your fan at different speeds during different times of the day is concerned, you've got me stumped. I've not run into any programmable rheostats with timers on them or anything (I live in the states), although I've never really looked. I can ask a couple of friends who still work at grow shops and see if they know of anything, but you might just be SOL.

Ok as far as worst case scenario I follow ya on those #'s

now on runnin two diffrent speeds at diffrent times..

i figured out how to but cost wise IDK

basically it would involve
two speed controllers
2 timers
and
a power strip or two
and some splicing

if you run power from one strip
24/7 then set the timer on variac for say 12am-noon then the other time from 1201 to 1159
both speed controllers would have to be piggy backed /attached to the fan..

could work??

 

[DeJa]

What if I got a lower cfm fan and just had it run full speed during lights on


then I could have the variac kick in at lights off and lower it down to 60%


My only problem is I don't want it to be too loud.

i feel like having a stronger fan running 35% and 70% would be much quieter

however if I am going to have to splice my fan cord, i think it might be a no go


anybody got any other ideas? =]

 

[Philosophelon]

What if I got a lower cfm fan and just had it run full speed during lights on then I could have the variac kick in at lights off and lower it down to 60%

The problem with that is that your fan has to be plugged into the variac in order for it to be able to kick in at all. In order to have your variac kick in at lights out, you would still have to go in at lights out and turn your variac down from 100% to 60%, or unplug your fan from a regular outlet and plug it into your variac which is already set at 60%.

That being said, if you spliced another plug onto your fan, plugged one into a regular receptacle and one into a rheostat-controlled receptacle (variac) and installed a timed relay to switch current between the two receptacles (like a tiny flip-flop box), it would work. But that will be kind of expensive and requires some electrical knowledge and experience, and may be dangerous (i.e. start a fire) if you do it wrong.

 

[DeJa]

DAG NABBIT



maybe i will just get a big fan and run it at 60% all day every day.


will that get expensive???


do most people run their fans that much?


would it be better to just hook up the fan to a thermostat that turns it on when the room needs cooling?

 

[Philosophelon]

I run my recirculating scrubber 24/7, because I have sealed rooms. If I had vented rooms instead, I'd run the exhaust 24/7, to keep smell from escaping. It's pretty standard to run either a recirculating or exhaust carbon scrubber 24/7, and a fan's power draw is minor compared to the draw of lamps, A/C, dehuey, etc.

 

[DeJa]

what kind of increase in my electricity bill should i expect?

with 1000w hid, fan running 24/7 and possibly an A/C

 

[DeJa]

hey guys i got another question


the grow tent is 160 cubit feet [5x5x6.5]

it will be in an 810 cubic foot room [9x10x9]

the door will remain closed, for obvious reasons


so how much heat is going to build up if I have my fan on 24/7?


am i going to need a source of fresh air or possibly an A/C?


i have central air conditioning that turns on about 3-4 times a day, but i dont know how much that will help.


and i would rather run an A/C in the room rather than cool my whole house, just to drop temps in the grow room.

there is a window, but i think we all know leaving that open will be a bit sketchy as my neighbors window is directly across, both on 2nd floor

 

[Philosophelon]

what kind of increase in my electricity bill should i expect?

with 1000w hid, fan running 24/7 and possibly an A/C

That all depends on how much electricity costs where you live. It's easy to fairly accurately estimate your electrical cost.

1) Figure out the total cost (including taxes and shit) of each kilowatt hour.

2) Figure out how many kilowatt hours each piece of equipment in your garden will use each day.

For example, a 1K mag ballast uses about 1.1Kw, and multiplied by 12 hours in use each day, your 1K mag ballast uses 13.2 Kwh/day.

Another example, say your can fan uses 200w, multiplied by 24 hours in use each day, your fan uses 4.8Kwh/day.

And so on with A/C, dehuey, oscillating fans, etc.

3) Add up the total Kwh draw per day.

4) Multiply your daily total by 30 to get your total monthly Kwh consumption.

5) Multiply your total monthly Kwh consumption by the cost per Kwh.

6) That's how much it's gonna cost ya per month.

 

[Vegan]

That all depends on how much electricity costs where you live. It's easy to fairly accurately estimate your electrical cost.

1) Figure out the total cost (including taxes and shit) of each kilowatt hour.

2) Figure out how many kilowatt hours each piece of equipment in your garden will use each day.

For example, a 1K mag ballast uses about 1.1Kw, and multiplied by 12 hours in use each day, your 1K mag ballast uses 13.2 Kwh/day.

Another example, say your can fan uses 200w, multiplied by 24 hours in use each day, your fan uses 4.8Kwh/day.

And so on with A/C, dehuey, oscillating fans, etc.

3) Add up the total Kwh draw per day.

4) Multiply your daily total by 30 to get your total monthly Kwh consumption.

5) Multiply your total monthly Kwh consumption by the cost per Kwh.

6) That's how much it's gonna cost ya per month.

nice informative post

 

[petemoss]

DeJa,
dongle69 posted a pic of a fan speed controller that should work for you. Her post is here:
http://www.icmag.com/ic/showpost.php?p=2082072&postcount=21

 

[Vegan]

DeJa,
dongle69 posted a pic of a fan speed controller that should work for you. Her post is here:
http://www.icmag.com/ic/showpost.php?p=2082072&postcount=21

nice unit!!!!!!!!!!!