Ventilation into dark room
From The Star And Shadow Cinema Wiki
Hi Ian,
So it seems 10 air changes per hour is sufficient, but others have put it at 20 for smaller rooms. How about we aim for between 10 and 12? Or maybe just go with 10. By my calculations, the room is approximately 10'x10'x10' - so 1000 cubic foot. The calculation above, to work out 10 air changes per minute, suggests dividing the cubic footage by 6 = 167 cfm. So per second its about 2.7 cfm. So if we go for 10 air changes per minute which is more than we thought (4!) is the power of the vent as important as the width of the ducting? The other thing is how to make it light tight...
Anyway, hope below is enough info for ya.
here are some useful links:
http://www.darkroomsource.net/ventilation.shtml
http://www.richards.uk.com/smallev1.htm - shows a similar dark room installation for a slightly smaller room, using 100m pipe.
Christo
Installing a fan for ventilation ventilation fan Selection criteria
- The volume of air must be sufficient to cycle the air in the darkroom at least 10 times per hour. To calculate this number, multiple the room dimensions and divide by 6 (a 4' by 6' by 8' room is 192 divided by 6 is 32 cubic feet per minute (cfm). When buying a fan, get one that does at least that many cfm (my 8x8x8 room uses 100cfm).
- The best fans I found were ceiling mount bathroom fans, the come with a louver, and are built into a metal box, with tabs for nailing onto 2x4 studs.
- You can mount this fan in the wall or make it into a portable unit, if you use the portable unit, you will still need a way to vent through a wall to the outside. I recommend in the wall, it is much simpler!
The easy answer is to buy a darkroom fan and darkroom vents. These are manufactured devices that are light proof and have a fan or not.
I would be careful venting into a crawl space. I would run a duct from the exhaust to the outside.
For 880 cf, you want a fan of between 88 and 220 cfm. That will give you between 6 and 15 air changes per hour. Remember to take into account that ducting will reduce the air flow of the fan due to backpressure (technically static pressure losses).
The best setup for a darkroom is a combination of positive and negative pressure ventilation. You blow filtered air into the darkroom and you power exhaust air at the same time. You size the fans such that you blow in slightly more air than the draw out. This way any leaks leak air out of the darkroom, rather than in carrying dust.
THe best place to exhaust is over the sink. This way the chemical vapors and dusts are removed closest to the source. The absolute best way is via a slot hood. This is an opening about 1-2 inches high the width of the sink. This is the exhaust port. You then size the exhaust fan to suck about 200-400 cfm throught the slot. Antyhing from the sink rises slightly and then back and out the exhaust. I built this for my sink and it works great.
BTW my background includes industrial ventilation design for contaminant control. So I am giving you advice to make a GREAT setup. The other posts will work, maybe not as well, but they will work. The big thing is to exhaust near the source and get enough airflow.
-- Terry Carraway, September 01, 2000.
