Darkroom ventilation (choosing from two systems)

[arigram]

There has been talk about ventilation in the darkroom before.
What I need you to help with, is to choose between two different set ups that are offered by the same company.
Those two models are sold here and I am not willing to look for something else really, especially since its very hard to find most recomendations here in Crete, or even Greece. Also because of the bulk and weight I rather not order from abroad.

The two offers are made by an italian company, Aspira.
My choices are:

* a direct wall mounted air exhaust
- large size of 34x34cm sqaure
- needs a new hole on the darkroom wall around 26cm square
- gives me about 20-25 changes of air in an hour (680 m3/h)
- makes noise of about 49dB from within 1,5m
- will be mounted on the wall at the right of the sink, just where it ends
- it has grilles and opening and closing flaps
- comes with seperate speed control unit
- it doesn't really stick out much
- its the more expensive

* an in-line centrifugal fan
- can be attached to the same pipe I had of a dead exaust unit
- it will need a bit of pipe more to sit properly and protect the fan opening
- it will stick out (about 20cm diameter)
- it will give me about ten changes of air in an hour (235 m3/h)
- it doesn't have a speed control unit
- makes noise of about 62dB
- I can find larger and stronger models but they can become really large
- its cheaper

My darkroom for those who haven't seen it in the darkroom photo thread its about 3x3x2m.
Air will come in from the opposite end of the room via an air conditioning unit.
My darkroom is mostly in the open, apart from the wall that the sink rests against which is the wall of another similar room. All the other three walls are outside walls.

Please look at the included photo.
a) is where the direct fan will sit
b) is about where the in-line fan with a pipe will sit
c) is where the old unit was

What do you suggest?

 

[Robert Hall]

One thing to note is where the fresh air supply comes from. If it is the door, you will not get much of a help from a fan.

You need to have the fresh air come from one side near the bottom, and exit the other side, near the top.

Otherwise, it looks like any of what you have there will do.

Good Luck.

 

[arigram]

One thing to note is where the fresh air supply comes from. If it is the door, you will not get much of a help from a fan.

Thank you Robert.
I've noted that fresh air comes from an airconditioner at the exact opposite side of the darkroom, so its pushed in, filtered and its cool.

How many changes of air I need per hour?

 

[resummerfield]

Get the one with the most airflow (680 m3/h). Depending on how you arrange the make-up air, the air changes per hour will be less than advertised. Sometimes much less. And like others have said, locate the make-up air for cross ventilation. And, the high flow model is even quieter.

 

[Robert Hall]

Yes, Eric has a good point, and quiet is very nice. I run 2 600cfm fans, one in each room, I have the doors ventilated with light baffles. I have them set on timers that go on 4 times a day and I turn them on when needed as well during toning or some such.

 

[arigram]

I ended up buying the first one, the big, square type. Tomorrow the worker will come by to open the hole and I will fit it these days. The only concern I have is that it might not be light-tight so I might have to improvise something. I thought of a squared plastic garbage can that I can fit on the outside wall and make a hole in the bottom so the light doesn't enter.

 

[RJS]

If you set up so air is blown in you will slightly pressuize your room which is a good thing. Helps keep dust out. I did it this way with a squirrel cage blower and an exhaust vent in the door. I could hear things 'creak' a little when I turned on the blower so indeed, it did build slight pressure!

 

[blansky]

As I preach every time I see a darkroom ventilation thread, I cover my trays that emit fumes with plexiglass.

Fixer and selenium toner cannot be noticed in my darkroom even with the fan off.

So a huge abundance of air replacement is not as necessary.

Nice looking darkroom by the way, Ari.


Michael

 

[arigram]

Thank you Michael. I have trouble with humidity so its not as sparkling clean at the moment as it used to be but considering this was a post-war laundry room, it transfered well into a darkroom.

 

[Robert Hall]

sounds like a good idea. Here's to good air!

 

[arigram]

Light-tight ventilation

Just as I expected, the exaust is not light tight.
So, yesterday I bought a custom-made alluminum pipe to help with the matter. It still didn't make the system light tight even though the inside was painted black and the extension of the pipe is somewhat long. It must be the large opening (30cm diameter) that lets a lot of light in.

I have included a photo of the outside of the pipe and a diagram of it. In pinkish purple I have drawn what I think two or three pieces of sheet would act as baffles to elliminate the problem.
The alluminum corner is very expensive and getting another one apart from the cost would also mean that I will have to take the thing apart, take it back to the store and also its not a guarantee that it will work.

What do you think?
Will it affect the airflow too much?
Do you have any other ideas?

 

[Roger Hicks]

Dear Aristotelis,

My impeller isn't light-tight either (despite being sold as such) so I have a plenum chamber on the outside: essentially, a box painted on the inside with blackboard paint and equipped with baffles (also blackboard-painted) so the air can be sucked in freely.

At the other end of the darkroom I have an extractor fan venting into the space between the ceiling and the floor of the room above. The extractor is rated at a lower volume/minute than the impeller and is probably further constricted by the space into which it vents, thus resulting in a very, very slight positive pressure.

Our darkroom is the old wine cellar, maybe 200 years old, and the big problem is humidity: it's built into the side of a hill. We have to run a dehumidifier constantly, which warms the room quite a bit. Very welcome in winter; very unwelcome in summer.

There are pictures of the darkroom in the free 'our darkrooms' module in the Photo School at www.rogerandfrances.com. One of the tricks I'm quite proud of is the Nova
slot processor recessed into the work surface.

Cheers,

Roger

 

[Steve Smith]

Another idea. What about placing some sort of fairly coarse dark foam into the pipe (a bit like a filter)? Something about 50 to 70mm thick and cut into a circle just big enough to fit into the pipe and hold itself in place. Obviously it does not want to be so dense as to restrict the air flow.


Steve.

 

[DWThomas]

How about swiveling the existing ell to point upward and putting two more ells in to create an inverted U against the wall? All would painted flat black inside, ideally. You might want some sort of bracket or brace, or maybe just a fastener through the bottom edge to avoid it getting too wobbly.

(Excuse the 1906 CAD ...)

Dave T

 

[DWThomas]

More thoughts.

You could add one more ell on the bottom of the tube, ideally with the opening pointed north, or located such that it never gets direct sun.

In addition, a diagonally cut section of pipe could be added to shade the opening.

Obviously the more bends added, the more impedance to air flow, but I think this would be a reasonable compromise.

DaveT

 

[Robert Hall]

They're right, you need at least one more bend.

 

[arigram]

Another bend would cost a lot, can't I get away with it with three sheet baffles like I demonstrated?

 

[DWThomas]

Another bend would cost a lot, can't I get away with it with three sheet baffles like I demonstrated?

Maybe -- I'm certainly no authority on this stuff. I was thinking the bend might be a standard plumbing item something like what is called "stovepipe" over here. I would think you could cut some cardboard baffles and tape them in the way you show in your drawing. That would likely not be a permanent solution, but it would provide a way to try the idea. Looking at your picture, it occurs to me you could surround the bottom of the pipe with a box or upside down trash can or similar enclosure. Have a hole cut in the bottom (now facing up) to snuggly fit the pipe and seal the joint with tape and some sort of black goop. Cut part of one side out of the box or can, maybe even put in a screen or louvered baffle. Then orient the opening toward that wall to avoid direct sunlight entering, leaving enough clearance from the wall to get good air flow.

Just writing/thinking out loud here. I'm not a ventilation or darkroom construction wizard but those are ideas I would probably try.

DaveT

 

[arigram]

Thank you Dave for your ideas.

It seems in the end I only needed two alluminum sheets to act as baffles. Its completely light tight now.

I only have one question:
The frame of the exaust doesn't fit completely around on the wall. There is a metallic frame inside the wall though so it doesn't leak light or air and the fan doesn't "feel" those small openings on the frame.
Do I need to fill them so the frame sits perfectly?

 

[DWThomas]

I'm not sure I follow you here. The outside looks well sealed in the picture. If it's inside, I guess one question is does it leave voids that open into the interior of the wall -- that might result in dust being sucked into the room.

If it's a matter of the fan box/plenum or whatever not filling the wall opening, perhaps you could cut and fit some trim moulding around it, nailing it into the wall?

Is it a structural issue -- does the fan assembly wobble? Perhaps some wooden strips could be wedged in as shims. If it's just a cosmetic issue, you could probably even use some sort of tape to cover the gaps and paint it to match the wall.

So there's a few random ideas but I'm not sure if they address your problem.

Anyway, it sounds like you are making progress. One of these days I need to do some work on mine.

DaveT

 

[arigram]

Phew!
Its done!
After the constructing, the filling and the painting, I expect to move back to my darkroom tomorrow (after some time at the beach ofcourse). The installation of the new exaust gave me the excuse to take care of other things from electrical wires and new light to cleaning rust and wall painting. It took me a while because its not easy to work during August in Crete especially during a heat wave!
This is how the new exaust looks like now.

Thank you all again for your ideas and suggestions.