exhaust--how much

how much airflow would you need if you had roughly 80 cubic foot (3.5' x 4' x 6'5" OD) cab with 400w hps

the ambient outside temp is around 64

the max internal temp after baking with 0 airflow under direct light is 100... 6 inches off center 95... will not get hotter than that ever with zero airflow... no fans... no extraction

so with a circulation fan i'm guessing the direct light temp will drop to slightly below 95 and the off center in the upper 80s... i'll test that and update later on

light does not have air cooled hood

with that said... what kind of airflow would be needed to get it down to about 75-80... what size ducting do you think it would take... probably one smooth turn and one 90.. no more than 8 feet of duct... probably less...


the short of it: how many CFM and what size ducting would you recommend?


EDIT: to clarify... what cfm exhaust would i need... intake i can probably over do passively... could push it in if i wanted i guess but noise is an issue and i can take exhaust ... nevermind... just answer the question... lol

intake is what will really"cool the room of course with circulation its even better. Ive always went 1/4 cfm per cu. ft. so if you have a 500 cu. ft room you need at least 125 cfm exh. fan but the intake should be much more than this .. anyone else??!!

bumpity bump...

i ran an open door test... no circulation at all... just opened the cab door... temps dropped to 85 under direct light

so how many cfm will it take to swap out enough air to keep it cool?

i'm running a test now with door closed and circulation fan on... but i'm waiting for you guys to chime in before i make up my mind on exhaust

so the test today... direct light.. fan off... 104... direct light fan on... 97

open door... under 83 in less than 5 minutes... got bored after that

this is all with the circulation fan on


currently have the thermometer at canopy level but out of direct center of the light to see what the actual air temp is with the door closed

any thoughts?

6 inch ducting is what i ran with two 4 inch passive intakes.

https://www.rollitup.org/grow-room-design-setup/301332-close-finishing-400w-cab.html

so... door closed with circulation fan on low air temp is 97 at 18 inches from light

door opened for 30 minutes with fan on low air temp is 77 at 18 inches from light

so how much air flow will i need to get it around 77-80?

buggin69 said:

how much airflow would you need if you had roughly 80 cubic foot (3.5' x 4' x 6'5" OD) cab with 400w hps

the ambient outside temp is around 64

the max internal temp after baking with 0 airflow under direct light is 100... 6 inches off center 95... will not get hotter than that ever with zero airflow... no fans... no extraction

so with a circulation fan i'm guessing the direct light temp will drop to slightly below 95 and the off center in the upper 80s... i'll test that and update later on

light does not have air cooled hood

with that said... what kind of airflow would be needed to get it down to about 75-80... what size ducting do you think it would take... probably one smooth turn and one 90.. no more than 8 feet of duct... probably less...


the short of it: how many CFM and what size ducting would you recommend?


EDIT: to clarify... what cfm exhaust would i need... intake i can probably over do passively... could push it in if i wanted i guess but noise is an issue and i can take exhaust ... nevermind... just answer the question... lol

Click to expand...

the math is pretty easy. say if you want to exhange the air 5 times an hour you would need a 400 CFM fan for 80 Cubic Feet area. I would suggest if you want to cut down on smell as well as heat i would go with an air exchange of at least 5 times an hour. Just my thoughts. According to my CFM chart here on my desk a 6" round duct can handle about 150 CFM at .5 static pressure (resistance in the line).

Sour

how does that math work?? how do you get to 400 cubic feet a minute changing 80 cubic feet of air every 12 minutes?

that's what i don't understand

UNICRONLIVES said:

intake is what will really"cool the room of course with circulation its even better. Ive always went 1/4 cfm per cu. ft. so if you have a 500 cu. ft room you need at least 125 cfm exh. fan but the intake should be much more than this .. anyone else??!!

Click to expand...

http://www.briteideashydro.com/calc-calculator.php

this website would agree with you.... but i intend to do my intake passively so i should probably take it up closer to 80... which would be a 1:1 which maybe will be sufficient

wow some really good posts here anyway the key would be totol isolation . especially if outside temp is cool . I have 10 x 15 x12 with about 4400w. of light and i prefer clean intake and exit unless i can use to heat somthing else up with twin fans i.e. intake and exhaust . but with only one is fine w/ outside intake and external exit ofcouse . I do like the .025% per cu. ft. i will definatley do the math and get back

when i speak of intake and exhaust im talking strickly cooled lighting seperate from clean air in and out for entire room in my case overkill is always better but im sure it could be engineered per space!

bigdw said:

when i speak of intake and exhaust im talking strickly cooled lighting seperate from clean air in and out for entire room in my case overkill is always better but im sure it could be engineered per space!

Click to expand...

i'm saving the cooled light for the bump up to 600

for now the light is not cooled... just the room will be exhausted

but like i said 77 with the door open... so if i can exchange the air twice an hour (which we know isn't enough) that should be enough for the temperature


and on that note... i scavenged a microwave oven twin blower and a squirrel cage fan tonight for all of 0 dollars... i have a feeling either one will do the trick just fine... but it's nice to have options

buggin69 said:

how does that math work?? how do you get to 400 cubic feet a minute changing 80 cubic feet of air every 12 minutes?

that's what i don't understand

Click to expand...

what do you mean? 400 Cubic feet per minute fan would circulate an 80 Cubic foot area 5 times. It is elementry division. oh you quoted me but had a question about the original post? yeah i dont understand that either.

stonesour said:

what do you mean? 400 Cubic feet per minute fan would circulate an 80 Cubic foot area 5 times. It is elementry division. oh you quoted me but had a question about the original post? yeah i dont understand that either.

Click to expand...

yeah.. 5 times a minute

you're working in minutes then just happily converting to hours at the end without actually doing any converting... that's what i didn't understand... but i got it now

for anyone that reads this later or anyone wanting to contribute...

just adding a 6x5 inch passive intake and 4 inch round passive exhaust the high temp dropped almost 10 degrees to right above 90 and it took quite a bit longer to get there... (when i say passive i mean no fans at all... just open holes... the intake even has a light filter)


i have the microwave blower wired up with a power cord and plug from a pc power supply and then i have that wired to a 3 way light switch... the light switch controls low and high speed (which is built in to the blower fan)... and now i'm just waiting on a capacitor to start the motor (missing part)... and all that is installed inside a box i built that has a hole cut in it to attach the ducting and exhaust ports with the blower mounted air tight to the back side...
when i get eth capacitor i'll test it out... low should be good because high should be over 200 cfm based on generic microwave blower speeds

in the mean time i'm testing a pc fan from the power supply i destroyed to get power into my blower box... have that wired to a 12v power supply and inserted in the formerly passive exhaust future ducted exhaust hole... this thing is blowing dust around so it's moving some air... i'll bet the temps have dropped already but i'll check later on and report back

down to 87 in an hour with just the pos 80mm pc fan... i think the microwave blower will do fine

microwave vent blower rigged up with shitty leaky cardboard ducting got the temps down to 83 from 88 in a matter of minutes with the door closed... on low...

right now the duct is only a couple feet long but like i said it's a leaky cardboard box and tape concoction and it takes two 90 degree turns

okay... to update anyone that has these questions in the future...

I got the microwave blower all wired up and sealed inside a box with a on/off switch, three way switch to control high/low... cut a big hole in the back and attached it to 6 inch hard ducting... takes two 90 degree turns and seems to be keeping temps in the mid 70s... actually 73.8 on high... testing low now but there doesn't seem to be much difference

so in summary... that's three 6x5 inch (5x4inch effectively) passive intakes and one 6 inch hard exhaust line running through two 90 degree turns and being pulled by a OTR microwave blower motor... 400 watts of hps in about 75 cubic feet wooden cabinet... also has one 8 inch and one 4 inch fan inside for circulation

so far the temp on low is 75.6

we'll see what happens after a full 13 hr cycle with the door shut most of the day (if i can control myself) tomorrow

should be about to turn off now

That's some great work you did figuring it all out like that. I would like to know what the ambient temperature is at this point since that will certainly affect temps inside. Is it still the same? Better yet, how much warmer inside is the box compared to ambient? I would expect a similar ratio regardless of outside temp.