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


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#1
jcj77d

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


#2
Tihspeed

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#3
jcj77d

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#4
Tihspeed

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#5
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#6
whitekush

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@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 :D

#7
jcj77d

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#8
jcj77d

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#9
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#10
Tihspeed

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#11
jamesreed

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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.

#12
jcj77d

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#13
jamesreed

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(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.
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#14
Tihspeed

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#15
jamesreed

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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.

#16
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#17
jcj77d

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#18
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#19
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#20
Tihspeed

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