Darkroom Ventilation Design.

[Bill Kumpf]

It is time to upgrade my sink and ventilation system. The ceiling fan in the converted bathroom just isn't doing the job. I thinking of an outlet duct just above tray height on the sink back with a fan mounted in the attic. This would be combined with a filtered inlet fan to create a slight positive pressure.

After viewing several treads here and a web search I have not found the air flow rate and velocity required extract the fumes. One site refers to a Kodax recomendation of 75 fpm at the tray and a room exchange rate of 5 times per hour,

Does anyone have design criteria or recomend a reference source?

Thanks in advance

[Henry Ambrose]

Hi Bill,

I think ventilation requirements depend partly on the room size. My last darkroom was 6x8 feet with 9 foot ceiling. I used a smallish bathroom vent fan mounted in a shelf above the sink and at the far end of the room from the door. Fresh air entered through the entry door vent. This gave a nice flow across my sink work area pulling fresh air past me and sending the fumes out the side of the room. I think the air path may be more important than the amount that is moved.

I have some of this stuff (vent fan, door louvers, etc. in boxes here. My new darkroom (converted laundry room) has a vent fan and an entry that allows me to crack the door for air with no light so I don't need this stuff. If you can use it you can have it. I also have a nice used sink if you want one. I've moved and made a larger one at the new place. You can have the old one. Just come get it - I'm not that far away from you.

Henry

[resummerfield]

My darkroom is approximately 1800 cubic feet, so allowing for 5 air changes per hour, in theory I only need to run my system at about 150 cfm.

I have a variable speed 600 cfm exhaust fan mounted outside the darkroom, which pulls air from my backsplash which slightly overhangs a 9-foot sink, and a variable speed filtered inlet blower on the other side of the darkroom (inside) for positive pressure. In practice, I find it works best to run the exhaust fan at about 1/2 capacity and leave the inlet blower off, letting my make-up air flow through the inlet filters. Although this results in a negative pressure, it is much quieter.

I have 2 suggestions or comments for any new system…

First, duct the make-up air to the front of the sink. This set-up would flow air over the trays (covering your trays with an “air sheet”) and exhaust the air at the back side of the sink. You would need less air and thus have a quieter system.

Second, install higher capacity, variable speed fans, so you can adjust the flow to the conditions.

There is a good discussion of darkroom ventilation on this APUG thread.

[Drew Wiley]

I also recommend a pull fan with variable power mounted outside. Ideally, air should
be drawn across the sink away from you, not up past your face. And inlet air should
be behind you. The flaw in merely recommending so many CFM is that the formula
becomes drastically affected by both humdity and any corrugations or sharp bends in the exit path; and obviously, you can't create a direct exit of light will get in!
In other words, the more CFM, the better. You can always turn the power lower if
you have surplus in the first place. On a rainy or humid day, a 250CFM fan will only
move about half that amount at best. I really like something in the 600CFM range.

[Graham Patterson]

There's a side effect to fan location which may be worth considering. A ceiling mounted extract fan will also remove hot air, which may not be desirable all year round.

[Keith Pitman]

I can't answer your question, but this site: http://www.eepjon.com/ should provide some useful information.

[John Powers]

Bill,

I agree with all that has been said here and would ask if sound level is important to you? I built my darkroom 11x13 feet by 7’ 2” height in 2004. I have bad allergies, wanted a good flow of clean air, and quiet either as quiet or not intruding on a good sound system. Every bathroom fan I had heard was noisy and for me irritating. Many had very short life spans. Someone recommended Panasonic fans. I must admit that I had thought of Panasonic as sound and video systems.

All wall and ceiling joints are sealed with tape to avoid dust. The door has rubber insulation around it. I bought two inline fans that fit in the rafters. I used white septic system 4” PVC pipe coming down from the sealed rafters to an 8 foot sink along a basement wall. The two pipes come down to points at 2 and 6 feet at the sink back. The pipe on the developer, stop, first fix side of the sink has a T opening taking air in from either side of the pipe. The wash, second fix pipe has a curved 90 degree opening pointing at the second fix. The fans exhaust two feet to the outside through drier type trap doors. One does not want summer bees visiting the darkroom.

Air coming into the room goes through a high quality furnace filter into a wall fan on the wall opposite the sink. The fresh air comes by me over the sink and trays when I am standing at the sink. The fans are so quiet that I only hear moving air in the PVC pipes. There have been no maintenance or service problems in this time. The fans were mail ordered from a CA building supply distributor.

If you get up to the Cleveland, OH area you are certainly invited to have a look.

http://www2.panasonic.com/consumer-e...00000000005702

John

[Roger Thoms]

Hey, don't forget to filter your make up air. In my last darkroom I incorporated a 3M furnace filter into the make up air vent, worked like a charm, and don't forget to change the filter periodically because it will get dirty.

Roger