Darkroom Exhaust Fan(400 CFM) For Positive Pressure, Plus DR Design?

[Drew Wiley]

Guess there are some people that can't appreciate true cleanroom standards in a personal darkroom. Maybe they enjoy endless spotting; I dunno. A true HEPA "system" traps all the air via tight gasketing and conveys it through the filter, both preventing any other route of airflow which might either damage the motor or might allow fine dust any alternate path out. This also makes a real difference, as someone already noted, at the mounting station. Permanent cold mount foils, now routinely used for color prints, are extremely unforgiving. If dust gets stuck there, that's it. Then when one is doing even ordinary framing using acrylic, which is quite electrostatic, any dust or lint around the room is going to spell a serious headache if it gets trapped behind, and you have to take the whole frame apart to remove the "fish" (the term used by pro framers) from within the fishbowl. So I don't know what Jac means by "our darkrooms". But it doesn't sound like any kind of darkroom I'd want. Those of us who once did a lot of big Ciba prints know what kind of hell its own electrostatic properties
were capable of. Working clean was not an option; you either did it or went both broke and insane.

[Luis-F-S]

Thanks so much Luis. It is of great help.
Let me please try to understand what you mean exactly.

There are four(4) fans, only, No louvres.
Two(2) Fans are fit on the door for Positive Pressure(intake). The other two(2) are on the other side of the same wall, for exhaust(draw air out). No passive louvres.
If I understand you correctly, you mean to take one Positive Pressure Fan from its sealed place in the door, leaving only the opening, beside the other working Positive Pressure Fan.
My apologies Luis if my understanding is not correct.
I think that will disturbs the Air Pressure Gradient. Plus, some light will leak from the corridor to the darkroom.
The same case for Positive Pressure Gradation, even if I replaced the Positive Pressure Fan, with a light tight passive louvre.
.

What actually happen, is connecting each two(2) fans in each area, to an extension power cable with individual "On/Off" switches. If I need two(2) fans to work together, will use the main switch, if I need only one(1) to work, will use the individual switch.
.

I may settle on this solution.
But before that, I wish I can validate my primary design(or any better alternative) through this thread.
Until now, I do not know if inverting exhaust fans(to work as Positive Air Pressure), is appropriate or just arbitrary experimental?
Appreciate your input.
Regards.

Doran fans have 2 louvers to make light tight. If you remove one it doubles the fan output.
Read the instructions on the fan.

[Drew Wiley]

Those Doran light traps aren't perfect. Their intake vents are best installed on the side of a building normally shaded, or else mount a simple shade above them. Set them in with dark adhesive caulking, not clear. Same goes for fans. Another reason I prefer an exterior mounted fan with a long indirect duct.

[Jac@stafford.net]

So I don't know what Jac means by "our darkrooms". But it doesn't sound like any kind of darkroom I'd want.

Just curious - do you wear long sleeves, a hair net (even if no hair), face mask and cotton gloves in your ideal darkroom?

[Leszek Vogt]

There are many ways to do this. Not really understanding the layout....I could offer this...

**Fans by Fulltech Electric (sold by Jameco) 226 CFM each (120V) - they force air out
**The sketch is an overkill on light tightness (loosely based on Chris's idea)
**If the window is sliding then it could be installed and part blocked with plywood piece

You can install more than two fans if you desire. Care must be taken to make sure critters don't have a chance to get in via the duct. Don't have the data how quiet the fans are. I have installed Broan (super quiet - not the conventional type) fans in the bathroom and they are still quiet - 10yrs later. Panasonic fans seem to be even quieter. I've stood appx 2 ft away from one and could barely hear its purrrrring. Both fans can be installed on individual switches/dimmers....or just one. Any sort of rubber type gasket (in the install) will help preventing metal to metal noise. You can also add an inline fan (depends on you) to force the air out more efficiently. Good luck.

Les

[Drew Wiley]

Hi Jac. Depends on what I'm doing. For film work I swab down the entire cleanroom, ceiling to floor. The room is equipped with an industrial air cleaner and triple filtered air. I wear an all-dacron cleanroom smock, which resembles a full-length lab coat but generates no lint. Last time I bought one it was only about thirty bucks, so these are certainly reasonable for every darkroom worker who wants to reduce spotting. In my case, where multiple contact negatives or masks might be required for a single color image, every bit of dust prevention up front is worth it. 8x10 film ain't cheap. But because this particular darkroom is my smallest and easiest to keep comfortable in winter, I also do black and white printing in there, but never at the same time as color work because fiber based paper obviously generates some fibers. I have a different room where the big 8x10 enlargers are, cutting table, etc., and yet another room for mounting prints. The sink room is separate from all of this, and no, I don't wear cleanroom gear in there, just chem gloves etc. Then the shop is peripheral to all of this, but itself quite clean due to the kind of equipment I use (otherwise, I do woodworking outside under a covered porch). Having a HEPA dust extraction system saves tons of time during shop work, well worth it, though I'll admit I had an inside track acquiring it. Every single serious cabinet shop and museum shop in this area is now equipped with that sort of clean machinery, otherwise
they would no longer be competitive. Working clean equates to working efficiently, which in turns means working profitably. Certainly not every photographer is going to have this kind of gear, but the same basic cleanroom habits are applicable everywhere, even with digital printing operations, because dust removal isn't fun in that case either. I'd think one would want to be rather fussy about the topic when scanning. Hair and beard covers aren't at all unrealistic in cleanrooms; in fact, they're mandatory in industrial ones. It takes half an hour just to suit up in the pharmaceutical labs. That amount of fuss would obviously be overkill for any darkroom; but still, perusal through a cleanroom supply catalog or website can teach photographers about numerous ways to save headaches down the line. You must be of my brother's generation. He passed away, but I still remember his first professional darkroom in an old barn in Santa Barbara with the walls lined with Natl Geo maps, and that old hairdryer-looking Beseler enlarger which he bought second-hand. It doubled as a bathroom. That old building probably sold for several million bucks later on, given its proximity to the beach. He did well in photography for awhile, and then got tempted to become a local realtor himself. But he'd farm out color printing to me.

[Duolab123]

My biggest source of contamination is ME. I sometimes think I am shedding more than my cats. I leave any street shirts out of the darkroom while I'm printing. I wear a clear t shirt and a cap. And then I'm very careful. Who ever is in charge at Ilford, get rid of the static black plastic bags, maybe Lead would work :-) . I still have some of the nice old Kodak 3 ply bags, craft paper on the outside, with plastic /metal foil laminate on the inside.
I got my hands on one of the old Kodak 5kV static eliminators with a camel hair brush. Boy that gets rid of static on plastic. It's a bit intimidating, turn it on and it's humming, you can smell, Ozone??? Dust is a pain.

[Luis-F-S]

Those Doran light traps aren't perfect. Their intake vents are best installed on the side of a building normally shaded, or else mount a simple shade above them. Set them in with dark adhesive caulking, not clear. Same goes for fans. Another reason I prefer an exterior mounted fan with a long indirect duct.

If you would read the OP's posts, he said that the intake and exhaust are located on the same wall in an interior corridor. Mine exhaust to an exterior wall and I've never had an issue with the factory louvers. Doran fans have a double louver to make light tight enough (though maybe not for Drew), you can often remove one of the louvers and double the flow. It might be better if you fur down and build a plenum over door to extend the full 4.5 m length of the wall; put an A/C register with an air filter for the intake of the plenum and then install the fans on the plenum. You should paint the inside of the plenum black. You could then center the fans a little better on the plenum rather than on the same wall as the exhaust.

You can look at how I did the exhaust in my darkroom to get ideas, except I used it on the exhaust and you would do the same on the intake. L

[Drew Wiley]

Intake and exhaust vents in proximity is counterproductive - risks drawing the fumes right back in.