IAQ options
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Thread: IAQ options

  1. #1
    Join Date
    May 2004
    Posts
    58
    I know this has been beat to death on here, BUT.

    Climate = Maryland (mixed humid)
    House = 2 story cape, open great room, SPRAY INPLACE FOAM
    Dual Infinity heat pumps.

    This house is getting a dehumidifier w/fresh air intake.
    While this will controll indoor humidity, is it enough for air exchange in a tight house ? or should an ERV be added for winter time use and the Ultra-aire for summer ? While the ultra-aire has fresh make up air, it does not extange as an HRV/ERV would.

    I would seem that I need 2 systems to takle 2 seperate issues.

    The HVAC contractor has an April-air ERV sitting in the basement (it is bought and paid for), but I am trying to hammer out exactly what systems I realy need and want in this home.

    Any idea's , TB?

    Thanks,
    Nick

  2. #2
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,633
    You'd be better off posting in the residential section. Humidity control and fresh air intake is for HVAC pros and not the average IAQ person. Unfortunately this pro can't give you an informed opinion because my part of the country is very dry. Though I can say that knowing how much fresh air is enough is difficult unless you do a blower door test to determine natural infiltration. Of course, what blower door people won't tell you is that their test can be fairly accurate or it can be hugely inaccurate and they have no way of telling which it is. And of course, even if natural infiltration is perfect it's still better to seal that down to as near zero as possible and control the ventilation mechanically. Is that clear as mud?

    [Edited by Irascible on 02-19-2005 at 12:44 AM]

  3. #3
    Join Date
    Aug 2003
    Posts
    626
    I use a blower door as part of my services, so I guess that makes me a "blower door person". I can tell you that if done properly they are accurate. Tests using tracer gas have confirmed this. Blower doors have been used for more than twenty years with exellent success and are a valuable tool.

    In terms of this particular problem, you have to do the math. An HRV will save energy over the Ultra-air. Are you going to live in the home long enough to repay for the initial cost? That is the question you have to answer. One of the most cost effective methods I use is Aircycler with a Hoyme motorless HRV, and a stand alone dehumidifyer like Sante-Fe.

  4. #4
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,633
    On average they're accurate. On a specific house they may not be.

    Take a (hypothetical) hermetically sealed two story house. Punch a fat hole in the wall of the upstairs bedroom near the ceiling. Then make the same hole on the opposite wall downstairs near the floor. Stack effect and winds will both make for a nice breeze through those holes. Now take the same two holes but put them near the floor on the lower level right next to each other. Same size holes, but now the infiltration is vastly different. No stack effect and no winds to help.

    A blower door can identify an amount of leakage based on a purely hypothetical environmental condition. Namely, it tests as though the pressure on the house was exactly the same on all parts of the house. But the pressure is not the same in the real world. And the location of the leaks has a big impact on how much leakage occurs. Hence my statement remains true. I know it’s not in the manual. But the manual doesn’t tell you what they don’t want you to know.

  5. #5
    Join Date
    Aug 2003
    Posts
    626
    One doesn't use a blower door to test for very accurate natural infiltration. One uses a blower door to determine the effective leakage area or "size of holes" or the cfm flow into and out of the home at a set pressure level. This can give a person who is experienced in this procedure the information on how much air is to be brought in mechanically. You are correct in saying one should tighten the house as much as possible and mechanically ventilate. In spring and fall when there is little difference in indoor/outdoor temp. and little wind--all homes no matter how many holes, are underventilated.

  6. #6
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,633
    Originally posted by uktra
    One doesn't use a blower door to test for very accurate natural infiltration.
    Well good. At least that makes you different from the blower door dudes I've met thus far. You may notice that in the sentence right before my statement regarding a blower door's potential inaccuracy I mentioned infiltration. Infiltration is what I was referring to. So we both agree that natural infiltration is very difficult to determine. And we both agree that a blower door is quite good at figuring out how big a hole the house has.

  7. #7
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,232
    Originally posted by nicholasa
    I know this has been beat to death on here, BUT.

    Climate = Maryland (mixed humid)
    House = 2 story cape, open great room, SPRAY INPLACE FOAM
    Dual Infinity heat pumps.

    This house is getting a dehumidifier w/fresh air intake.
    While this will controll indoor humidity, is it enough for air exchange in a tight house ? or should an ERV be added for winter time use and the Ultra-aire for summer ? While the ultra-aire has fresh make up air, it does not extange as an HRV/ERV would.

    I would seem that I need 2 systems to takle 2 seperate issues.

    The HVAC contractor has an April-air ERV sitting in the basement (it is bought and paid for), but I am trying to hammer out exactly what systems I realy need and want in this home.

    Any idea's , TB?

    Thanks,
    Nick
    In your climate, a ERV will not save enough to pay for itself. The Ultra-Aire will provide enough fresh air throughout the year to provide oxygen, make-up air and purge pollutants. But if I had the ERV on site, paid for and I was into technology like you are, I would install it and play with it. If your home is all spary foam insulated, you will need some winter ventilation. ERV saves $50-$75 a season. Use the UA for spring, summer, and fall to provide make-up air and positive pressure during high outdoor humidity.

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