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  1. #40
    Join Date
    Sep 2011
    Posts
    36
    Quote Originally Posted by breathe easy View Post
    Frankly, I would go with the Honeywell media filter base. You can buy replacement filters in a MERV 11 which is probably all you need. These filters are easy to find, relatively inexpensive, have low pressure drop and should last about 6 months. No need for a pre-filter. They should capture somewhere around 95% of airborne allergens.

    If allergens are a problem, you might also check my post on the "In search of better air" thread.

    We are testing the HC16 now. The initial tests are right on the money. Very efficient and 0.31wg pressure drop. However, to achieve this they probably had to charge the heck out of the fibers which will neutralize in about a month. (meaning pressure drop will go up and efficiency will decrease dramatically) Efficiency has dropped from 85% at 0.3 microns to 79% in the first week. We have had to temporarily stop the test. Should start up again later this week. If it turns out OK, I will let you know. If you go with the Honeywell, you can always switch to the HC16 since the filters are the same size.
    I am considering going to a non-electronic solution based a consumer reports article recommendation for the LENNOX HC16 (and by default HC10). Specifically: Honeywell F100, MERV 11 with a sp drop of .23. I think this is the one you are speaking of above.

    Can you help me not with a particulate efficiency question, but with a question on resistance efficiency?

    The static pressure drop on many electronic units ranges from .18 to .27. In the same range as some of these 4 or 5" thick non-electronic media filters.

    How can I think of pressure drop when:
    - eg my AHU/DUCT system measures .5 SP no filter in? ( I chose .5 as I read this is a max objective for sp on a system)
    - filter sp rating is .25
    - filter note says filter at .5
    - the AHU operates up to .8 sp

    So when filter is new, sp is starts at .5 + .25 = .75.
    This looks to me like I only have .05 of static to raise before I have to replace the filter!!

    Is it correct to think of this that way? Margin for loading the filter with particulates is way too low?
    What am I missing?
    Thanks

  2. #41
    Join Date
    Sep 2011
    Posts
    36
    Quote Originally Posted by pmeunier View Post
    R J Cedar, your situation is a textbook case for using a HEPA filter. Connect the intake of the HEPA filter to the woodshop area, and the exhaust in the heated area. Have a smallish passive vent between the two that will complete the air path (so the air speed through it >500 fpm but not high enough to whistle much). Because the woodshop will be under continuous, strong negative pressure, only a little will escape when you'll open the door, and whatever does will likely be captured back after the door is closed. If you do this then you don't have to worry about anything regarding your regular HVAC unit, if it doesn't have any duct connecting to the woodshop area.
    Ok, thanks.

    So this would be the same as a in-shop room air filtration system, but instead of the air circulating in the shop, it would discharge into the house circulated air (which I was trying to keep isolated from my dusty air) (but now it would be as clean as the filter would allow) and the passive return would allow heat pump heated air back into the shop so I would then not have to heat that separately.

    Maybe then too, I don’t have to worry so much about going to a filter in the AHU that would capture any escaped woodshop dust, as the HEPA installed as you describe would do the main work. Not sure I need to go HEPA….. MERV 15…..do you think so? I guess that would be safest. Espeially if I forgot about going to a MERV 11 filter in the AHU and went to the MERV 5 my contractor wants to put in which has an initial SP rating of only .08. So low. 5" media and elecontronic SPs are up around .23 or so, so much higher I have concerns with that as expressed in the post above.

    Are you thinking of a home made blower in a box and just stick in a HEPA filter?

    You mentioned a smallish passive return. Why smallish?
    This IS A REVIEW OF WHAT I HAVE: tHE smallish passive return gives the shop negative pressure and minimal return of house air back to the shop. In the AHU area which is in a heated area of the basement, there are 3 ducts out from the AHU - study, hallway, AHU area. The cold air return for the basement is in the hallway (to move it further away from the woodshop) and it is sized so there is a positive pressure to the heated basement area, so the woodshop air does not drift into the clean area...the clean air drifts to the woodshop, not the reverse. Given that, we now have +ve pressure in the clean air zone and -ve pressure in the dirty air zone....so...even more clean air flows to the woodwork shop. Ok that is good. Dont want the reverse. What you suggest works with what was earlier planed.

  3. #42
    Join Date
    Aug 2003
    Posts
    906
    Quote Originally Posted by R J Cedar View Post
    Are you thinking of a home made blower in a box and just stick in a HEPA filter?
    I wasn't. It's possible for someone to make something better than what is being sold as residential HEPA filters. You could also make a filter box with a MERV x filter and some blower. However, I think it's better value and much easier to buy something like a Fantech HEPA as a starting point. You could build a pre-filter box for it to be able to use cheap standard furnace filters (e.g., MERV 11) and extend the life of the HEPA media itself.

    COPD is for life, do yourself a favor and don't skimp -- get a HEPA filter. The finest dust is the worst for your lungs and that's what a HEPA filter captures.

    Quote Originally Posted by R J Cedar View Post
    You mentioned a smallish passive return. Why smallish?
    The larger it is, the more it will dissipate the negative pressure in the woodshop, and allow particles to escape. If it's too small, the door will be difficult to close, you'll get loud whistling, the filter won't have good air flow and the motor could overheat while consuming more electricity. So, there needs to be a vent, but of a size that is small enough to have a resistance to the air flow to maintain the negative pressure.
    -If you won't turn it on then nothing else matters.

  4. #43
    Join Date
    Aug 2003
    Posts
    906
    RJ, I found this link which recommends venting outside:

    http://billpentz.com/woodworking/cyclone/index.cfm

    Doing that would also maintain a negative pressure in the shop. In any case, the HEPA filter would only protect people in the rest of the house, and wouldn't be sufficient to protect you or anyone else in the woodshop.
    -If you won't turn it on then nothing else matters.

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