Discussion in 'Smokers Lounge' started by Justcheckingitout, May 22, 2018.
Exaust will go outside
For the exhaust to flow outside, just as much air will have to come in to the house from somewhere. If the house was perfectly sealed, the air couldn't flow. You ok with air leaking into the house from outside through every crack and crevice?
I was looking at it like a air cooled hood, with the exaust fan on the left side of the hood and the fresh air duct open on the right, now picture the hood as a sealed grow cab, the exaust suckung would not be sufficient to pull in the air from the fresh air duct? Just a thought, I am second guessing my self on putting a Sep can fan to push air inside. It seems The vent for fresh air would be about 5' from cab. I am going to draw a pic with dimensions of whole set up planned and see if you guys get what I am thinking,
Edit: I just re read the last post and get what your saying now OldSmokey....my confusion on my part... thinking having a open end air intake to the cab would cause a smooth exaust flow...here is the pic below I was talking about. The fresh air duct would be going into cab from the bottom...I drew it by mistake going in on top....
Do you use the dryer? Probably not a good idea to tap into the exhaust if you do.
78F in the house... With AC? If so, you'd be better off dumping the exhaust into the house and having the AC cool it again. I guess it would depend on the temp outside.
You mentioned having the air inlet at the bottom of the cabinet. In addition, having the inlet pick up air at floor level is often helpful to get the coldest air.
Edit: Maybe dumping exhaust air back into the house would cause a big problem with excess humidity and require a dehumidifier running all the time.
I do have a dehumidifier in my house ac, I use the dryer but am thinking of just running exaust to roof vent in attic at roof top edge. I was thinking grow cab for flower is only going to be 2x4'-5'x 6' high that's 60 sq feet max. Was rule of thumb 3x sq exaust set up? If so I will prob need to pump in fresh air, I hadn't thought about the rule of thumb.
I may have missed it but what room of the house will the grow cabinet be in Check?
I always try to pull air from as 'cool' a source as I can and looks like you have that covered. Venting air out is not so big an issue so long as you have the smell aspect covered. A suggestion would be to use...forgive my pun here... a 'check' valve (aka one-way valve) downwind of your exhaust fan if you are going to use the dryer vent as your exhaust route. That way you allow your vented air to past through, but none of the dryer air can enter the grow. Of course that would depend on your fan being running or not. If it's running then dryer air should not backfeed since the pressure is less than your exhaust fan. You are correct on your rule of thumb too. At least that's how I always heard it. You want to be able to remove at least 3x's the volume of air in the growspace in one minute.
Does the rule of thumb change when LEDs are the light source?
That's a good question. I know my cob LEDs run 10* cooler than my 600 w hps.
Copied from RIU, posted by "coreywebster":
This is not my work, its copied from another forum. Credit goes to Anonamiss.
It boils down to CFM = 3.16 x Watts / DT(°F)
Watts is the lighting power (and any other 'hot' things in the grow space) in Watts.
DT is the allowable temperature rise within the enclosure (i.e. desired temperature minus ambient temperature) in °F.
So, to work out the size of fan required (in CFM) simply plug your lighting Wattage into the equation along with the DT value.
An example is:
Ambient temerature = 20 °C
Target temperature of the enclosure = 25 °C
DT in °C = 25 - 20 = 5
DT in °F = 5 x (9 / 5) = 9
Lighting Wattage = 250 Watts
Plugging these values into the equation gives:
CFM = 3.16 x 250 / 9 = 87.77
This represents the actual throughput required but it doesn't take account of the static pressure necessary to overcome the system impedance (how hard the fan has to suck or blow). But for a free-air system with no ducting or filters it should be fairly accurate.
For those who want a bit more info on how to work it out, here it is.
First, you'll need to know the amount of heat that needs to be dissipated.
The general equation for heat transfer is:
q = Cp x W x DT
q = amount of heat transferred
Cp = specific heat of air
DT = allowable temperature rise within the enclosure
W = mass flow
Mass flow is defined as:
W = CFM x Density
DT is the difference between the ambient air (room) temperature and the target temperature inside the grow space in °F.
At sea level the density of air is 1.2041 kg/m3 (at 20°C) and the specific heat capacity (under typical room conditions) is 1.006 kJ/kgC. After doing some substitution and conversion this gives:
CFM = 3.16 x Watts / DT(°F)
I saw this the other day and thought it might be useful. I haven't tried out the formula in the real world, but it seems to suggest I have more than twice the fan power that I need. No wonder my garden is chilly.
That's why I use a fan speed controller. My fan is way over-sized but I can always reduce the airflow if need be. Better to have and not need...etc etc.
That's my issue. I got a 375 cfm fan and if I ran it at high speed it would suck more air than needed, wasting my frosty ac. It's so dam hot again I wait till 8pm to mow yard.
That's some good info Oldsmokey. We should sticky that somewhere.
Same here...100 all damn week long.
I got to figure out how to do the doors....any good ideas on how to go about it? It's really the only thing I have never been able to do good.
Yeah doors are a B I T C H....or can be. Do you have pics of them for reference? Inside and outside...angles. That sorta thing would be helpful.
I have no clue what I am going to do. Last time I used flat hinges and tried weather striping but still had gaps.
Can you possibly hang something such as black plastic from the top, inside of the cabinet, across it's full width, and to the bottom.....right behind the doors? Maybe even heavy white plastic. I seem to recall seeing some that was black and white on opposing sides. That way you just create a false front and the doors simply secure the cabinet.
If you are going for stealth and no hermies, zero light leaks are allowed. With my cabinet, having the doors seal perfectly isn't as important as keeping the light where it belongs. Check out the gap in the gasket at the corner. It's not leaking any light though.
One thing that I found important was to paint black the surfaces that mated with my door gasket and the areas where any leaking light would hit. If I left the surface white, it leaked lots of light. Also, having a recessed door kept people from sighting down the edge of the door into the gasket area.
I recessed the hinges into the door with a router and a jig that I made up. Apparently I went a bit too deep. The hinges aren't real heavy duty, so I made up for it by using a lot of em. Seven on each side. Each door is half a sheet of 3/4 plywood and even that isn't enough thickness to keep the door from flexing outward. It needed the aluminum angle to give the edge enough rigidity to remain straight...
One thing about door gasket: Sealing requires compressing the gasket ever so slightly. Lots of linear leet of gasket requires lots of pressure to compress. That caught me by surprise, though it shouldn't have.
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