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  1. #11
    Sean's Avatar
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    Thanks all, well I made some progress. I found a few remaining air leaks coming from the bottom of one of the walls. Nothing some spray foam couldn't handle. After sealing those leaks I could then feel a gentle air coming through the intake vent. The fan is rated for a room 20x20ft and with my new wall in the darkroom in now 17 1/2 x 11ft, however the ceiling is on a slope up to 9ft so that ads extra volume. I'm not sure if I'll need a vent hood or not? Is there a trick to determining this? Would like to hear from people with a darkroom my size to see what they do. Also the fan's out nozzle had a stamped metal cover with holes in it (I assume to keep critters out), I got a nibbler tool and cut that out and I think it's probably increased airflow atleast 20%.

  2. #12

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    In my last company, we did a lot of work with an air-flow/extraction system that we used. For OSH and general comfort issues it was fairly important that we got it right, so we did quite a lot of investigation. The general steps to improving the efficiency were ...

    1. check the volume of air is not restricted at any point in the system. So the inwards vent should have the same size opening as the extractor fan. The idea is to keep the air flowing at a constant speed (i.e. not slowing down OR speeding up anywhere). Restricting the size of an airway will speed up the air; conversely increasing the size of an airway will slow down the speed of the airflow. A big darkroom will slow down the air so much that it would have difficulty being efficient (sorry).

    2. check for leaks that could bring in air from where you don't want it to.

    3. specific extraction points sometimes need ducting directed to those points (eg like the chem trays).

    The first two steps were considered necessary; and the last by assessment. First steps are probably easier, but if there is still a problem, then it might be more affective to draw the chem vapours off the trays before they are distributed into the general airspace of the darkroom.

    I have an aquaintance who recently set up her home darkroom after 20yrs professional B&W wet printing in a lab. She is elderly now, doesn't use gloves and her darkroom is relatively small. She did go to the effort of putting a hood over the trays.

    But like all things, just a suggestion! It may not be necessary.

    best,
    john.

  3. #13
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    Just give us a day or two, Sean, and we'll design a system of localized ducting that will require a 15hp, 3-phase motor to do the air handling. Then, you'll have better justification for installing your own power sub-station to handle that other big enlarger.
    [COLOR=SlateGray]"You can't depend on your eyes if your imagination is out of focus." -Mark Twain[/COLOR]

    Ralph Barker
    Rio Rancho, NM

  4. #14
    Sean's Avatar
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    Maybe I can purchase a used helicopter engine and place it on the roof

    Well, another long day working on the darkroom and 1st coat of paint is on, everything is sealed and spray foam under two walls that had big gaps (the joys of converting a garage!). The fan seems to be doing well, plenty of air coming out of it and when I put my face infront of the intake which is placed on the opposite wall/opposite side I feel a good breeze blowing in. I have a filter on the backside of the intake and the intake is a doran lightproof vent. Now eventhough a good breeze is coming out of the vent, when I open my darkroom door I can hear the exhaust fan rev up quite a bit. I suppose my light tight vent + filter media is decreasing the efficiency. Would it help much if I added another vent or maybe I need a better filter media that allows more air flow? hmm..

  5. #15

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    Sean. how noisy is it? I've got the smaller Dorian with matched inlet and it seems to do a decent job (I can tell the difference between having it running or not!) but it's very noisy. One day I'll move the thing somewhere further away by putting some ducting between it and my darkroom.

  6. #16
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    Sean, you might want to look into a residential kitchen cook top hood for the chemical trays (fixer area) as these are inexpensive and easy to install. Remember to keep the front edge where it is hard to bang your head on it. Do a mock-up by bending at the trays to make sure you have room for clearance. Paint the inside of any duct work with black paint and put in a couple of 90 degree bends to cut down on light, and a grill on the outside with a boxed cover and open bottom for air escape. You can get a small louver from a building supply which goes in a gable end (roof vent in the side wall).

  7. #17
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    The fact that the fan revs up tells me you are working a negative pressure balance in the darkroom and will tend to suck dust in from the outside every time you open the door. What you might eventually do if this bothers you is to put a fan on the intake side with maybe 50% more cfm capacity than the existing exhaust fan. This will reverse the pressure balance in the room, even a fractional psi on the positive will blow dust away from any openings in the darkroom. Both fans working together will insure an efficient air exchange.
    Gary Beasley

  8. #18
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    I did mine just the opposite - I put the fan/filter combination in the interior wall and over near the trays is just a vent to the outside. That way it sort of keeps the room pressurized and seems to help get rid of dust instead of sucking it in. I still avoid the flashlight test, though. I might see a dust particle and feel compelled to re-engineer the whole thing again, my wife would shoot me!

    BTW - I didn't want to pay the outrageous prices for the doran fans and grills, so I bought a (much quieter) 300cfm bathroom fan and constructed a light proof grill for it out of oak and 2" roof flashing. It works quite well and allows a good airflow. If anyone is interested I can work up a web page explaining the construction.
    Bruce

  9. #19

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    I think Bruce and Gary's suggestions are good too fwiw. The noise of the fan is something to be aware of.
    Generally the motors are designed for a particular airflow capacity. We previously attached ducting and airbags that were too big (and allowed too much air-flow) for the motor on an extraction system. As a consequence the motor speed up and came close to overheating. So, it may be more important to keep the air intake close to design levels rather than making it very much bigger. The documentation should have suggestions about that.

  10. #20
    Sean's Avatar
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    Thanks for the info everyone

    I still avoid the flashlight test, though.
    I wish I would have never picked up that flashlight! hehe

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