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

  1. #41

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

    but let me insist in the Behike test...

    Just we smoke a bit the Cohiba to obtain nice "smoke threads" floating static in the air, when we start the fans we have to see how the "smoke threads" (specially those on the trays) go to the outlet smoothly, showing that fluid on the areas emiting fumes go to the outlet without mixing in the rest of the darkroom. This is the ideal situation, with a moderate flow we keep fumes far from us.

    If we don't get this then we'll need a large flow and anyway we'll be in contact (more or less) with the fumes.

  2. #42
    Drew Wiley
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    Re: Darkroom Exhaust Fan(400 CFM) For Positive Pressure, Plus DR Design?

    No generic figure can be given for the number of "air changes" needed. It depends on what you are specifically doing as well as the overall efficiency of your exhaust system. If you work with color chem or certain kinds of alt chemistry, you probably need at least the capacity for more air exchange than for ordinary black and white work. For mixing noxious stuff I supplement my big fume hood with a mini fume hood on a flexible hose connected to a booster fan which feeds into the main system. It is noisy, so I only use it only briefly on demand. I also have a secondary hood over a drum processor, likewise feeding into the main duct. But most color work I run in a separate portable drum processor outdoors, because I'm slightly allergic to RA4 fumes. The inline Panasonic Whisperlite fan which I use for my bathrooms in the house rather than darkroom is 440 CFM, extremely quiet, and is mounted in the attic, roof-ducted, rather than on an outdoor wall. Highly recommended. You
    can adapt them for indoor wall mounting if needed - unsightly, but a simple box could be built around them in the darkroom.

  3. #43

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

    Do I understand correctly that the ft2 of the inlets should at least equal ft2 of the outlets, regardless of push or pull? How do the length of the duct runs (and their size) figure into the calculations?
    --- Steve from Missouri ---

  4. #44
    Thalmees's Avatar
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    Re: Darkroom Exhaust Fan(400 CFM) For Positive Pressure, Plus DR Design?

    Quote Originally Posted by Pere Casals View Post
    As you see, ...
    ...
    Pere, I'm unable to thank you enough for your input.
    Thanks sooooo much.
    Will comeback with to comment and final(hope) request after I draw a better refined design.
    Best Regards.

    The generosity of spirit in this forum is great, its warmly appreciated.
    ------------------------------

  5. #45

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

    I must be the outlier here. best labs I've worked in had L traps passages so no push, but good ventilation/ exchange thru several large ducts (one of which is maneuverable to place over trays or while mixing dry chemistry). Never noticed any more dust in these darkrooms either. tbh, I really dislike doors in darkrooms
    notch codes ? I only use one film...

  6. #46
    jp's Avatar
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    Re: Darkroom Exhaust Fan(400 CFM) For Positive Pressure, Plus DR Design?

    My experience in moving air is to keep computers cool and clean in small datacenter environments.. Dust prevention is the same goal for the darkroom. Positive pressure is good if you filter the air being forced in. Clean air leaking out the door frames or other leaky places is better than drawing in dusty air from other places. We had an economizer bringing in outside air. I used quality hepa furnace filters to keep it clean, then it was positive pressure from the air handlers to move it to it's destination. When that wasn't needed, the filters cleaned the circulated air conditioning.

    In a darkroom, find a readily available size of hepa furnace filter and put it over your intake air. You'll lose a little flow, but it will be clean fresh air. Make a box around it, and slide in new filters when needed.

    I have the same Honeywell hepa air cleaner in my darkroom. It keeps my negatives drying dust free. I would like to add fresh air at some point as it heats up in the summer while I work in there and gets cool in the winter. Most likely I'll use a Panasonic bathroom fan and build a light tight box for the air path.

  7. #47
    Drew Wiley
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    Re: Darkroom Exhaust Fan(400 CFM) For Positive Pressure, Plus DR Design?

    While home air cleaners can be helpful is many situations, there is a big difference between something containing a so-called HEPA filter and a true HEPA system. Most items marketed as HEPA do not even begin to meet the EPA definition of that term, let alone more stringent EU requirements. I call it the BS coefficient. HEPA furnace filters are another example of abuse of the terminology, though they obviously have legitimate applications. I sold millions of dollars worth of true HEPA equipment over the last decade, prior to retirement, related to potential control of actual toxic dusts. There are all kinds of devices out there that are not properly rim-sealed regardless of what the filter itself is. Stuff gets around the filter. Fortunately, in most darkroom situations the intake vents merely need to filter out dust to a minor degree. If you need true HEPA intake air, maybe you should move! I can sympathize with anyone with pollen allergies, etc., but those are fairly large particles. Why do I even bring up this kind of seemingly nitpicky distinction? Well, it can make a big difference if you are planning to experiment with a photographic process requiring toxic powders like chromium salts that you don't want accidentally dispersed, or need to clean up after an accidental spill. I've met quite a few artists who have serious long-term health effects from that kind of scenario. Otherwise, for garden variety black-and-white printing, a certain amount of compromise in fuss and economy is generally OK.

  8. #48

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

    Quote Originally Posted by Drew Wiley View Post
    so-called HEPA filter and a true HEPA system.
    HEPA flters range from E10 to U17, all are true norm EN 1822:2009 HEPA filters. Performance depends on the specified grade...

    HEPA filters, as defined by the United States Department of Energy (DOE) are H13 in the European Union. See Specification section here:

    https://en.wikipedia.org/wiki/HEPA

    Those that are used by lots of people suffering allergies (pollen, acari) are an overkill for a drakroom. For example my cheap Honeywell 16000 is H13.

  9. #49

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

    Quote Originally Posted by Luis-F-S View Post

    Just don't go crazy with it and don't loose any sleep over it.
    L
    From post #9............you may want to disregard a lot of the next 40 posts.
    L

  10. #50
    Drew Wiley
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    Re: Darkroom Exhaust Fan(400 CFM) For Positive Pressure, Plus DR Design?

    Luis - these threads get perused for all kinds of reasons besides the original question. So a bit of info overkill might be of real benefit to certain people. For example, in some parts of the country, a darkroom might well be constructed in a basement with radon issues. There are basic timed, automated easy-install fan systems from these same manufacturers designed to address that specific problem. In urban areas like around here, darkrooms and other craft spaces are often put in old industrial or military buildings with serious hazmat issues. Some of these involves rental spaces where a neighbor might be carelessly spraying something hazardous. The average photographer or artist tends to be very naive about these risks.
    You can personally do everything right yet be affected by something else nearby. Less than a year ago, I attended the funeral of a friend who died at 34 due to merely living adjacent to something like that, and there was another friend not long before. Several others are terribly ill due to being exposed to substances in those kinds of buildings. I've seen people with hair falling out and all kinds of wierd cancers, kidney failure, you name it. Don't assume anything... And Pere, you seem to rely a lot on generic Wicki information. I have an actual EPA Instructors license related to hazmat. I haven't renewed it because I'm retired now, and it's expensive to do so. I'm not guessing about any of this. I've worked directly with the German engineers in charge of designing the proper kinds of extraction equipment that is now sold worldwide. And EU standards are in fact way more stringent than those in the US. If you want to learn about it, there are Govt manuals as thick as a phone book - quite different from a brief Wiki paragraph. But your description of smoke studies in confined spaces is certainly helpful. That also applies to getting properly fitted with a respirator when basic room control itself is not adequate. They are tested in small smoke chambers. Due to all the tech industry around here, there are a number of businesses entirely dedicated to industrial safety as well as cleanroom supplies. For others, I recommend LSS (Lab Safety Supply) as a web or phone order source - huge selection of not only safety gear but also all kinds of lab items useful to any serious darkroom.

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