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  1. #1
    Join Date
    Oct 2008
    Location
    Berlin, Maryland
    Posts
    9

    Energy Recovery Ventilators (ERV's)

    I was reading a brochure printed be a home performance company that stated (ERV's) typically make summertime mold and humidity problems worse, not better. Anybody know why?

    Mike

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,644
    This is one of the great mistries of life. First, congrats on your concern for getting real fresh air into your home. Any good a/c guy here nows that you should do everything possible to avoid getting fresh air into your home because it causes mold and dust mites.
    Green grass climates have outdoor dew points of as high as 75^F. For comfort and mold/mite control, you need <55^F indoor dew point inside your home. ASHRAE suggests an air change in 4-5 hours to purge indoor pollutants and renew oxygen. This is about 80-100 cfm of fresh air. With high cooling loads, your a/c easily removes the 3-5 lbs. of moisture per hour to keep the home dry. With low/no cooling loads of cool wet weather, the a/c is unable to keep the home dry. Your home would grow mold. Appreciate their concern for avoiding fresh air??? I agree better to breath polluted, low oxygen air than have moldy home.
    When the wind is at +10 mph, even a tight home leaks enough fresh air to get enough fresh air. When the wind is calm, even leaky homes get very little fresh air.
    They are right that you a/c is unable to deal with moisture without significant cooling loads.
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  3. #3
    Join Date
    May 2012
    Location
    San Diego, CA
    Posts
    352
    Yep, if you let in humid outside air the ERV doesn't work well in removing the humidity. Check to see if your AC/thermostat if you can run the air to dehumidify or is your unit only temperature based.
    You can call me Sam

    It should be a crime to be a mechanical engineer in San Diego
    Summer Design Temperature: 83 F Dry Bulb ~ 69 F Wet Bulb (California Climate Zone 7)

  4. #4
    Join Date
    Aug 2003
    Posts
    907
    TB, your sarcasm might confuse beginners...

    To the OP: bringing any humid air into your home will increase the humidity. Using an ERV to do so is better than using a fan, but it still brings in humid air. In either case you need some way to dehumidify the air. The people you talked to probably meant that *needlessly* running an ERV is a bad idea. However, you need fresh air to be healthy, and you need to dehumidify it to prevent high humidity issues like mold.

  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,644
    Quote Originally Posted by pmeunier View Post
    TB, your sarcasm might confuse beginners...

    To the OP: bringing any humid air into your home will increase the humidity. Using an ERV to do so is better than using a fan, but it still brings in humid air. In either case you need some way to dehumidify the air. The people you talked to probably meant that *needlessly* running an ERV is a bad idea. However, you need fresh air to be healthy, and you need to dehumidify it to prevent high humidity issues like mold.
    Thanks for pulling me up a little. I am a little frustrated by the lack of concern by the a/c trade to provide fresh air as part of the package. Sarcasm/humor is fine line. Keep me in line.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

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