Need some ideas from some true Tech's/DIY'ies

Ok, so im having heat issues, not all the time, but IMO, any build-up of heat, isnt good.

my setup:
4x4x7 tent
400-1200w MH/HPS (currently running 1200w, dual 600w HPS)
Hydrofarm Radiant AC 8
8" inline duct booster fan 500cfm (exhaust)
8" window fan 500cfm

i have my hood connected to about 2-3ft of ducting that attaches to my 8" exhaust fan, which connects to about 4ft of ducting, which is connected to the 8" window fan (set to exhaust, which helps assist the duct fan from bogging down).

temps can reach to mid 90's depending on time of day.

so heres my idea on "boosting" my CFM's, or just to make a better exhaust fan, money is super tight ATM, so..........

I have lots of 120mm/4" CPU/axial fans, rated between 118cfm to 80cfm, & a few other sizes of CPU fans as well.

my idea was to take 3-4 of my 120mm (12v, .9amp, 118cfm), & somehow group them together to make 1 bigger fan, & then take this fan & either put it on the inside to push (boost) air through the booster/duct fan, or pull air through the other end (like the window fan) to help boost the booster/duct fans cfm/rpms.

these 118cfm fans are very very strong, considering they are .9amp each, just need somebody to so me how i can get them to fit into a 8" configuration to hook up to the 8" duct fan to boosts its cfm/rpms.

i plan to use 1-2 of my collection of cpu fans to build a carbon filter.

fyi, i have about 7-8 120mm fans, 2 80mm fans, 2 60mm fans, & various others laying around, all new, so if that helps.

so i just need help in designing a way to put them together in a group, or in a housing to hook up to the booster fan

Edited by jcj77d, 30 October 2010 - 12:36 AM.

is there any way you can air cool just your light with maybe room air? or room air to light to exhaust just the light?... this might solve your heat issues.. and then just lots of pc fans to just cool down your grow...

I actually read some place that you can stack pc fans, like literally stack them, and it helps.. but to what degree i don't know... and at what cost... but like you said you have lots of them you can plug a couple together real quick and see

I don't know what hemisphere you live in but its winter bro.... and its 90 in your grow space not cool(no pun intended)

where are you taking your temp readings?
pictures? grow space and fan locations will help.
exhaust temp?
intake temp?

is there any way you can air cool just your light with maybe room air? or room air to light to exhaust just the light?... this might solve your heat issues.. and then just lots of pc fans to just cool down your grow...

I actually read some place that you can stack pc fans, like literally stack them, and it helps.. but to what degree i don't know... and at what cost... but like you said you have lots of them you can plug a couple together real quick and see

I don't know what hemisphere you live in but its winter bro.... and its 90 in your grow space not cool(no pun intended)

where are you taking your temp readings?
pictures? grow space and fan locations will help.
exhaust temp?
intake temp?

im growing in a tent, using passive intake (air from outside the tent, room air), so i am pulling in air from the room, & i have 2 clip fans in the tent, 1 6" (160cfm), & 1 7" (190cfm) clip fans.

Ive asked that before, & was told stacking pc fans doesnt do anything, except increase their ability to move air through static pressure, it doesnt increase cfm's or anything like that, but i was told if you somehow left a 1/2" - 1" gap when stacking pc fans, & make the gap where air can easily be pulled in, & not pushed out, you MIGHT get a slight increase in cfm's.

down south, where its hot 90% of the time.
@ canopy level, no current pics, but look through my "threads" not posts, & i got an old old vid on youtube, search "green bud".
grow space is 4x4x7 tent in a 10x10x9 room, house ac is at 74f, but the room is warmer b/c of the tents radiant heat, & i dont measure exhaust/intake temps

90 most of the time is nice... with a slight breeze

Ok it wont hurt much to try this...

use some ducting and use room air to only cool the light and vent this outside the way you have it

use the pc fans to exhaust your grow space... maybe all of them...

when i get home ill do some math to see how many.. but your gonna have to use all your tents vent holes unless you can pony up some cash for a Duct fan like you already have... those are cheap anyway... but i believe this will solve your problems

whats the distance between your canopy and air cooled hood?

or.....

use your highest CFM rated fan and use that to only cool the light..... either exhausting into the room or to the outside.... just not with grow space air...

this might work as well... either way its easy to do and cheap..

@OP,

Friends tell me that using your highest CFM on the light would reduce alot of heat.

also since youre using duct, i use a duct inline fan going to some flexi-duct going out my window, but you could easily throw another inline fan in your set up, thats why they're inline

90 most of the time is nice... with a slight breeze

Ok it wont hurt much to try this...

use some ducting and use room air to only cool the light and vent this outside the way you have it

use the pc fans to exhaust your grow space... maybe all of them...

when i get home ill do some math to see how many.. but your gonna have to use all your tents vent holes unless you can pony up some cash for a Duct fan like you already have... those are cheap anyway... but i believe this will solve your problems

whats the distance between your canopy and air cooled hood?

i cant, the hood is so big, that there is no space to add ducting to both ends & still be able to zip the tent up, i prob could, but the ducting would get smashed, which would just reduce the air flow.

the glass is between 2" away, from 12" away, taller plants are on the outside, shorter plants are in the center, & i could get the hood closer, but then i get light bleaching

or.....

use your highest CFM rated fan and use that to only cool the light..... either exhausting into the room or to the outside.... just not with grow space air...

this might work as well... either way its easy to do and cheap..

i do, this is how it is:
hood ===> ducting ===> 8" 500cfm exhaust ===> ducting ===> 8" 500cfm window exhaust to outside (not room, but outside).

i think im gonna try to take 1 of my 118cfm fans & place it inside the housing of the 8" exhaust fan, having it blow directly on the fans blades, to see if this boosts the 8" fans speed

@OP,

Friends tell me that using your highest CFM on the light would reduce alot of heat.

also since youre using duct, i use a duct inline fan going to some flexi-duct going out my window, but you could easily throw another inline fan in your set up, thats why they're inline

thats how i have it, & i would get another duct fan, but have zero $, so why not use these pc fans i bought to cool the tent since i already have them

zero dollars get's you only as far as your feet can carry you

they make a dryer extender... it for like a four inch duct... but im sure they would make it for larger models, or you can make your own...
[ame=http://www.amazon.com/Tite-Fit-Dryer-Ducting-Degree/dp/B000H5OM34]Amazon.com: Tite Fit Dryer Ducting, 90 Degree 21" to 42": Patio, Lawn & Garden[/ame]

this way you can air cool only your light... all you would need is some cheap steel and some rivits or foil tape

Simple fix if I understand your situation correctly. You don't have an air movement problem that would be fixed by fans alone. You have an air flow problem. You state that you are using two 500cfm exhaust fans to dump air outside of the building envelope, and that that air is being pulled passively from the ambient in the room your tent is setup in; but you don't state how you are replacing that 1000cfm within the building. You are essentially attempting to vacuum out all the air in your house without a new supply. Something no combination of inline fans is going to overcome unless they are powerful enough to face an exponentially increasing static pressure.

Assuming you have 2 6" exhaust ducts (in bathrooms) and one 4" exhaust duct (over stove), you have a building capability of 750cfm of air replacement (providing all your weather sealing is up to par); and that's only when none of your building exhaust fans are running. In short, your maximum air supply is 250cfm short of your maximum exhaust capability.

The solution:

(1) 1000cfm is roughly 2.5tons of air conditioning. So in order to control your temps 100% you would need a minimum of a 2ton AC unit pulling in outside air. That's not going to be cheap!

(2) Since the laws of thermodynamics tell us that temperature exchange (cooling in this case) happens whenever 2 objects vary in temperature, and the temperature of your light fixture is undeniably higher than the outside air temps; You could just open any window in your house so that the open area = 72" Sq or more. If you want the air to be cooler when it reaches your tent, open the furthest window away. And if you wish to keep the humidity down in your home, you could run a 8" duct from said window to the intake side of your air handler so that the drawn air is conditioned upon arrival. None of that is ideal, but its near free for now.

If that doesn't resolve the problem in the short term, report back with the exact sizes of the passive intake vents in your tent.

Simple fix if I understand your situation correctly. You don't have an air movement problem that would be fixed by fans alone. You have an air flow problem. You state that you are using two 500cfm exhaust fans to dump air outside of the building envelope, and that that air is being pulled passively from the ambient in the room your tent is setup in; but you don't state how you are replacing that 1000cfm within the building. You are essentially attempting to vacuum out all the air in your house without a new supply. Something no combination of inline fans is going to overcome unless they are powerful enough to face an exponentially increasing static pressure.

Assuming you have 2 6" exhaust ducts (in bathrooms) and one 4" exhaust duct (over stove), you have a building capability of 750cfm of air replacement (providing all your weather sealing is up to par); and that's only when none of your building exhaust fans are running. In short, your maximum air supply is 250cfm short of your maximum exhaust capability.

The solution:

(1) 1000cfm is roughly 2.5tons of air conditioning. So in order to control your temps 100% you would need a minimum of a 2ton AC unit pulling in outside air. That's not going to be cheap!

(2) Since the laws of thermodynamics tell us that temperature exchange (cooling in this case) happens whenever 2 objects vary in temperature, and the temperature of your light fixture is undeniably higher than the outside air temps; You could just open any window in your house so that the open area = 72" Sq or more. If you want the air to be cooler when it reaches your tent, open the furthest window away. And if you wish to keep the humidity down in your home, you could run a 8" duct from said window to the intake side of your air handler so that the drawn air is conditioned upon arrival. None of that is ideal, but its near free for now.

If that doesn't resolve the problem in the short term, report back with the exact sizes of the passive intake vents in your tent.

ok, the window fan is a dual 8" window fan, each fan operates separately, so 1 of them is off (it needs to be fixed, it got wet, & now its very loud & squeaks, dont need that) & is use as a passive intake ATM, & inside this room is a AC vent, & a 1' x 1' connecting vent that connects to the next room, & ive checked to see if my setup is fighting any static pressure from the house, by opening the bedroom door, & then an door to the outside, & there is just barely barely a slight increase in the fans exhaust speed (i can hear it), & ive left it like that & the temps only dropped by 2 degrees, but thats b/c its pulling in cooler air from outside the room, but i cant keep the door open b/c of pets, security reasons, & it makes my AC run more, which = higher electric bill.

passive vents on tent = 3" x 2' flap, & there are 3 of them, all at the bottom, & are open

(3) 3"x24" openings would accommodate a maximum of 750cfm (3 x 250cfm) at the indistry standard static pressure of .1 IOW/100' (what most exhaust fans are built to overcome). So you are running a negative pressure for the building and the tent. Environmental design is difficult to accomplish from off-site, but if you're willing to try a few things, we might be able to sort it out. You may well need more than 1000cfm of exhaust to displace the heat build up from a 1200x HPS, but you are at capacity at the moment and that must be dealt with first.

First, Open one of your tent doors by 72" sq (3x24, 4x18, 9x8 etc) do not go overboard, stay as close to 72" as you can. Note whether the exhaust RPMs increase or not and what the tent temperature is, and then leave that flap open for the next bit.

Now,

You state that you have a 12"x12" transfer duct/vent to the next room, but also that the room has minor negative pressure which results in an rpm increase when the door is opened? Or does the RPM only increase when you open an outside door?

Do this,

Open the bedroom door with all outside doors closed. If the RPM increase is present when you open the bedroom door, remove the transfer vent and measure the actual duct size. 12"x12" duct should allow 850cfm; combined with the AC vent (what size is the AC vent ducting), you should not have a negative pressure for the room. Note your findings. Now close the bedroom door but leave the dent door open. Then open a window in another room and note if you detect an RPM increase. Then open the bedroom door with the window still open and note if you detect an RPM increase. Now, with the window and bedroom door still open, close the tent door and note if the fan slows down.

If the RPM increase is only present when you open the window, then you can leave the bedroom door closed and the tent door and window open. If you notice an increase when you opened the bedroom door, then leave it open as well. With the necessary air paths open, wait one hour from when you opened the tent door and noted the temp, then note the new temp and report back all the data from the above inquiries here.

(3) 3"x24" openings would accommodate a maximum of 750cfm (3 x 250cfm) at the indistry standard static pressure of .1 IOW/100' (what most exhaust fans are built to overcome). So you are running a negative pressure for the building and the tent. Environmental design is difficult to accomplish from off-site, but if you're willing to try a few things, we might be able to sort it out. You may well need more than 1000cfm of exhaust to displace the heat build up from a 1200x HPS, but you are at capacity at the moment and that must be dealt with first.

First, Open one of your tent doors by 72" sq (3x24, 4x18, 9x8 etc) do not go overboard, stay as close to 72" as you can. Note whether the exhaust RPMs increase or not and what the tent temperature is, and then leave that flap open for the next bit.

Now,

You state that you have a 12"x12" transfer duct/vent to the next room, but also that the room has minor negative pressure which results in an rpm increase when the door is opened? Or does the RPM only increase when you open an outside door?

Do this,

Open the bedroom door with all outside doors closed. If the RPM increase is present when you open the bedroom door, remove the transfer vent and measure the actual duct size. 12"x12" duct should allow 850cfm; combined with the AC vent (what size is the AC vent ducting), you should not have a negative pressure for the room. Note your findings. Now close the bedroom door but leave the dent door open. Then open a window in another room and note if you detect an RPM increase. Then open the bedroom door with the window still open and note if you detect an RPM increase. Now, with the window and bedroom door still open, close the tent door and note if the fan slows down.

If the RPM increase is only present when you open the window, then you can leave the bedroom door closed and the tent door and window open. If you notice an increase when you opened the bedroom door, then leave it open as well. With the necessary air paths open, wait one hour from when you opened the tent door and noted the temp, then note the new temp and report back all the data from the above inquiries here.

wow, where have you been? Nice deduction. Way to read threw the build without pics. Welcome to the site. Hope you picked a chair. This was a good read

Thanks for the welcome. I'm just trying to get jcj77d through the next month or so and then (even here in FL) the outside temps will solve his heat problem long enough for him to afford a more permanent solution. This is one of the reasons I avoid duct booster fans when designing AC systems. Their ability to overcome static pressure is very limited as they are designed to run optimally only when being forcefully supplied by the air handler. The 500cfm rating is likely not even close to what it is pushing with all the resistance being encountered. If it weren't for the window fan lending a hand, it would have probably shit the bed by now.

Well I can't wait to read your responses on new builds. Please take the time to spell things out for people. I'll be reading bro. I'll thank you for pot god. I keep reading thew you post seeing all the venting angles your looking at. It seems clear cut but it's not. And I have to do some more math to get everything your calculating. Crazy

(3) 3"x24" openings would accommodate a maximum of 750cfm (3 x 250cfm) at the indistry standard static pressure of .1 IOW/100' (what most exhaust fans are built to overcome). So you are running a negative pressure for the building and the tent. Environmental design is difficult to accomplish from off-site, but if you're willing to try a few things, we might be able to sort it out. You may well need more than 1000cfm of exhaust to displace the heat build up from a 1200x HPS, but you are at capacity at the moment and that must be dealt with first.

First, Open one of your tent doors by 72" sq (3x24, 4x18, 9x8 etc) do not go overboard, stay as close to 72" as you can. Note whether the exhaust RPMs increase or not and what the tent temperature is, and then leave that flap open for the next bit.

Now,

You state that you have a 12"x12" transfer duct/vent to the next room, but also that the room has minor negative pressure which results in an rpm increase when the door is opened? Or does the RPM only increase when you open an outside door?

Do this,

Open the bedroom door with all outside doors closed. If the RPM increase is present when you open the bedroom door, remove the transfer vent and measure the actual duct size. 12"x12" duct should allow 850cfm; combined with the AC vent (what size is the AC vent ducting), you should not have a negative pressure for the room. Note your findings. Now close the bedroom door but leave the dent door open. Then open a window in another room and note if you detect an RPM increase. Then open the bedroom door with the window still open and note if you detect an RPM increase. Now, with the window and bedroom door still open, close the tent door and note if the fan slows down.

If the RPM increase is only present when you open the window, then you can leave the bedroom door closed and the tent door and window open. If you notice an increase when you opened the bedroom door, then leave it open as well. With the necessary air paths open, wait one hour from when you opened the tent door and noted the temp, then note the new temp and report back all the data from the above inquiries here.

ive tryed this before, & there is only a slight rpm difference when i open an outside door, no matter which vents/windows/doors are open. yes there is a slight increase in rpms when i open the tent door, & temps do drop.

the screens on my tent vent/flaps are dirty, so cleaning them might help, + i have 2 6" round ducting holes/ties that are tied shut, 1 at the bottom, & 1 at the top, so i might take 1 of my 120mm 118cfm cpu fans & either use it as an exhaust for the top 6" vent, or as a intake for the bottom 6" vent.

the transfer vent duct is actually 18 x 18, & ac vent is 12 x 12, in both rooms

w/ tent closed & all doors closed, temps max @ 93, w/ tent door closed & bedroom door open, it drops to 88 (but makes house ac run more, not good), & w/ outside door open & everything else closed, temps are @ 92, & w/ tent & bedroom door open temps drop to 79, but i cant leave the tent open or the bedroom door, b/c the light from the tent (1200w) makes it to where you can see the light through the window, & i have dogs & cats & ferret, so i cant keep bedroom door open.

its getting cooler here @ night, so im gonna clean the tent vents, & try to fix the other 500cfm window fan, as intake

Thanks for the welcome. I'm just trying to get jcj77d through the next month or so and then (even here in FL) the outside temps will solve his heat problem long enough for him to afford a more permanent solution. This is one of the reasons I avoid duct booster fans when designing AC systems. Their ability to overcome static pressure is very limited as they are designed to run optimally only when being forcefully supplied by the air handler. The 500cfm rating is likely not even close to what it is pushing with all the resistance being encountered. If it weren't for the window fan lending a hand, it would have probably shit the bed by now.

100% spot on, & exactly why i attached it to the window fan, & i think somehow attaching a 120cfm pc fan blowing directly on the blades of the 8" booster fan will boots its rpms.

i mean these fans are strong, i hook them up to my 12v-13.8v 3amp dc power supply, & run the fans @ 13.8v the fan will hoover off the table about 1/8" like a UFO

i still had temp issues when i was running 360cfm + 500cfm, & the tent really had a negative pressure, the whole tent would suck in, but not as much as it does now

Well I can't wait to read your responses on new builds. Please take the time to spell things out for people. I'll be reading bro. I'll thank you for pot god. I keep reading thew you post seeing all the venting angles your looking at. It seems clear cut but it's not. And I have to do some more math to get everything your calculating. Crazy

i did thank him, using the rep system lol:D

i was not doubting you would at least say thanks.. i was just so impressed, especially from a new person... i just wanted to voice that in your absence he was thanked ahead of time... not trying to step on your toes...

hope you solve your problem... please keep us informed of your decisions... it will be interesting what you end up doing