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  1. #16
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    Feb 2016
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    There are always plenty of second hand "Buffalo" style gas heaters on Gumtree.

    These have a monster 12 inch fan in them. I know this as there is one here. I hate it. Its grossly inefficient. I was under the house just 3 weeks ago re-taping all the joins.

    Perhaps one of these fans ripped from an old unit? They are supposed to be variable speed (ours has an ancient controller).

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  3. #17
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    Feb 2016
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    Canberra
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    Default metre readings and Dr. Wood Dust

    I could imagine those air vents at commercial sites must be a new form of unholy hell. I shudder to think.

    ..

    On trying to get to a practical outcome, I thought to read a bit about what Bill Pentz and Matt Wandel say about such things. I found this article to be illuminating in many ways https://woodgears.ca/dust/dylos.html

    Especially about the needle felt filters and the use of various low-tech solutions (I remember BobL saying, a long time ago in a post on dust collectors and PF's, how efficient they really are, despite their apparent nastiness).

    Worth the time to read it, including the final thoughts and conclusions at the bottom....

    I really need to buy one of those 2.5ppm particle detectors. https://www.ebay.com.au/itm/Household-PM2-5-Detector-Module-Air-Quality-Dust-Sensor-Tester-LCD-Display-2-8/192876810276



  4. #18
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    Feb 2006
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    Perth
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    Quote Originally Posted by woodPixel View Post
    I could imagine those air vents at commercial sites must be a new form of unholy hell. I shudder to think.
    Doesn't even have to be commercial. Even in domestic situations centrally ducted AC has its problems with some bugs growing inside return ducting. Apparently human breath contains lots of ammonia and under certain conditions it plus other dust like skin cells condense inside AC return ducts where all manner of bugs feed and multiply on it. That's not usually the reason for using filters on the +ve pressure side of ducted AC but there would probably be more health issues if there were no filter. This is more of a problem in moist climates or where water leaks into an AC system. Legionella can also be spread via larger ducted AC systems.

    Especially about the needle felt filters and the use of various low-tech solutions (I remember BobL saying, a long time ago in a post on dust collectors and PF's, how efficient they really are, despite their apparent nastiness).
    Not sure what your are referring thin that last bit.

  5. #19
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    Feb 2016
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    Canberra
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    Quote Originally Posted by BobL View Post
    Not sure what your are referring thin that last bit.
    Youve written a few excellent articles that need to be pinned.

    This is one: How long does it take to "condition" a DC needle felt filter .... its from 2013!

    and there is another, which immediately comes to mind, that discussed several tests you did for colleagues on-site with their setups and leaks.... let me see if I can find that one.

  6. #20
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    Feb 2006
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    Perth
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    Quote Originally Posted by woodPixel View Post
    Youve written a few excellent articles that need to be pinned.

    This is one: How long does it take to "condition" a DC needle felt filter .... its from 2013!

    and there is another, which immediately comes to mind, that discussed several tests you did for colleagues on-site with their setups and leaks.... let me see if I can find that one.
    OK now I know what you mean. The same conditioning principle applies to most filters except HEPAs because they have to work straight out of the box.

  7. #21
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    Feb 2016
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    Canberra
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    Default MERV13 and the JET AFS2000 room air filter

    A question of a curious mind!

    If one were to run TWO filters, would the result be "better".

    I understand it will create a bigger pressure drop, but I've an opportunity to buy multiple for a low price.

    I've the Jet AFS2000. It uses a pre-filter of 20x24x2 at around MERV8. The primary internal bag filter is also 20x24 but is an 8-pocket type. Its MERV rating is utterly unpublished. Jet itself is absolutely appalling in their weasel-word non-explanation and should be the target of a lawsuit. Its evasive language and deliberate non-specificity leads me to think that it is no better than ABSOLUTE JUNK.... https://www.jettools.com/us/en/p/afs...control/708615

    The replacements are equally deliberately vague https://www.amazon.com/Jet-708723-AF.../dp/B0009H5RJI and even going to Actifil (Allwin), the makers of these filters, has ZERO information on them. Interesting considering every other product they sell has copious labelling as to efficiency.

    I wrote to JET to enquire.... silence.

    As I said. Untrustworthy junk.



    Now, I can acquire decent filters from a few places!



    AirePleat M13 HC Merv 13 508x610x100mm https://shop.airepure.com.au/1304202...0x100mm/pd.php @ $95

    FilterBuy USA - 20x24x4 https://filterbuy.com/air-filters/20x24x4/ .... Six for USD$119 and AUD$97 shipping (ShopAndShip.com)

    Bison CPF20244.13 https://www.bisonfilters.com.au/p-28...ant-media.aspx AUD$68 delivered.



    The US option is cheapest, but one needs to buy 6. I can acquire 4 at the same price, but the postage remains almost the same.... so may as well get 6!

    If I were to put TWO of these in the JET, would I be better off filtration wise?

    OR would I be better off using just one and leaving it on for longer?

  8. #22
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    Feb 2006
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    Perth
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    Quote Originally Posted by woodPixel View Post
    The US option is cheapest, but one needs to buy 6. I can acquire 4 at the same price, but the postage remains almost the same.... so may as well get 6!

    If I were to put TWO of these in the JET, would I be better off filtration wise?

    OR would I be better off using just one and leaving it on for longer?
    Filters in theory work like this. The theory is more likely to occur in relatively clean air to begin with but less so in a workshop situation.

    Lets say you have two filters that are 90% efficient at 1 micron or greater.
    In theory the first filter removes 90% of the dust and lets 10% through.
    The second filter removes 90% of the 10% or 9% of the original dust in the ant and lets 1% through.
    However, this assumes the dust particle size distributions stay the same (they wont) as the air moves it's way through the filters and there's no filtering effect of the dust clogging up the filters.
    If the two filters start out the same, the filtering effect of dust clogging up the filters is going make the first one in the air path remove more fine stuff as it ages which means the second one will do less and less.

    Coarser (Pre) filters are often used to protect finer filters in many applications. In the clean rooms we wold wash/replace pre filters every 1/2 months which meant the fine filters lasted for years and only replaced. If you cannot wash the filter repeated replacement becomes expensive. At work we experimented with using polyester fibre similar to that used in pillows as prefilter media. We bought a huge 2m wide roll of it and cut it up to suit. It worked quite well and it could be washed so we hardly used up any of the roll - I often wonder what happened to it. I also wondered what would happen if one just used polyesters pillow stuffing?

    Grey poly foam sheeting also makes a good prefilter and it's washable. Many commercial HEPA filter units come with these as standard. We tried using it in our labs but the acid fumes disintegrated it within a couple of years.

    My take on RAFs is you want them to removed the dust as quickly as possible so it doesn't settle out so its just as important to maximise air flow so as you say its aways a trade of between filtering the air more thoroughly with each pass or using more passes. I've done some calcs to try and model this but in practice only measurements will determine which works more effectively for a given situation

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