This tek is part of bod's cultivation is easy as fuck link list


Bod's Easy AF Laminar Flow Cabinet Build
Here's how I made my 24"x24" laminar flow cabinet

What I used.
Flanders Pureform High Capacity "nuclear grade" HEPA filter. New old stock.
24x24x12 0.004% (99.996%) with a SP of 1.60 Resistance (W.G.) at 2000CFM test
$150 shipped

Dayton 1TDU2. (new in opened box)
$165 shipped

4'x8'x0.75" piece of 5 ply void free Maple plywood
$53

Hardware, Silicone, Etc.. I had already but
$15-20

Total assembled cost = $368-388



To build a flow hood you need
A filter and a fan to work in harmony.
A HEPA filter can come in 99.97% or more efficient at 0.3 microns.
You ideally will build a hood with a HEPA filter that is 99.99% or more efficient.
A HEPA for laminar flow will be pleated and usually 5-12 inches thick.
As air flows through the filter there's a resistance. This resistance will change with the velocity of air through the filter. There's an initial resistance, a certain pressure that appears as soon as any air even begins to move through the filter.
YOU WANT TO KNOW the resistance the filter has at the DESIRED FLOW RATE for your FILTER SIZE.
AGAIN if you have a 24x24 that's 400CFM you want blowing at you (100FPM = 0.5m/s). so your filter needs to have give or take 0.8-1.2 INCHES Water Gauge (in.w.g.) at the CFM requirement your size filter needs for your flow hood.
My filter has resistance of 1.6 inches w.g. at a test flow of 2000CFM. The initial resistance is likely 0.8. I couldn't find the graph for my filter but likely at 400CFM the resistance the filter develops is above 0.8" and likely above 1" as well and quite a bit below 1.6" so this will work perfectly.
This is why it's called STATIC PRESSURE. Your fan will blow a CONSTANT VELOCITY against a CONSTANT RESISTANCE(at that velocity) your fan needs to blow your CFM requirement at the S.P. your filter develops at that CFM. it's a balancing act.

If my filter had a static pressure of 1.2" (guessing here but it's a close guess)
that means I would need a blower that delivers AT LEAST 400CFM(actually you want it to be able to deliver 20% more at least so 500CFM bare minimum to last the length of your filter getting progressively more clogged)

If your fan delivers more CFM at the resistance of your filter at the laminar flow velocity then you can always choke back the intake of your fan or stack pre-filters.
most blowers do not like speed controllers.

I used the dayton 1TDU2

here's it's graph
as you can see it delivers over 1000CFM at no resistance
and about 450 CFM at 1.6" of resistance


at 1.2" (my theorized filter's resistance at 400-500CFM) the 1TDU2 delivers over 800 CFM still
So this fan is more than powerful enough. Which is wonderful because I would like to use pre-filters in front of the blower to keep the HEPA lasting a very long time.

regardless you can always ask the manufacturer for any clarification needed

Quote:

Your filter is rated 500 FPM  ( 2000 CFM ) @ 1.6” WG.  The filter is scanned test @ 100 FPM as that’s the capacity of the test instrument.  Running the filter at 100 FPM will give you laminar flow below the filter.

Laminar flow is when the air flow  is 90FPM +/-  20%.  ( 72FPM to 108 FPM ).

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Basically you build a box around the filter that the fan can blow into. You want there to be a plenum, a space for air pressure to equalize over the back of the filter for even air flow. The plenum should be at least as deep as your filter is deep. In this case my box is 24" deep 12 for the filter and 12 for the plenum. If you can't build a box stop, this TEK isn't for you. you need to know how to wire a blower and build a box if you want to do this.

How fast can the flow be?
100 FPM is 0.5 meters per second.
Laminar flow can come at any speed even 1000mph but we want something we can work in front of. The flow needs to be fast enough to keep our work clean from contamination but not so fast it blows shit out of the way. So our limits are based on what's realistically usable. which is like 0.3-0.7m/s or 60-140 feet per second.

since we're usually dealing with perfect square feet(12x24 or 24x24 or even 24x36) or half square feet(12x18) it's easy to calculate CUBIC feet per minute or vice versa. as 100FPM over 1.5(12"x18")sq.ft. is 150CFM and likewise 100FPM over a 24x24sq.ft area makes 400CFM

Of course the lighter test is our "Scientific" approach to gauging the flow being correct or not. A flame from a cigarette lighter should bend at about a 45 degree angle 6 inches from the front of the filter when everything is all dialed in.


now get to work


oh wait I forgot something

that's more like it


more updates and pictures to come

Xerbia said:

Thanks man, nice write up. How long can one expect something like this to last?

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Tmethyl said:

You are a fucking beast Bodhi.
A very intelligent and helpful beast.



You use beer to make agar?

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