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  1. #1

    Condo building in Chicago is too humid in the winter (strange, I know). Thoughts?

    My condo building in chicago is a 4 story, 36 unit building. It was built in 2005. Bricks and concrete. The furnaces are electric furnaces (unusual, I know).

    Many of the units are way too humid in the winter, causing lots of condensation on the windows that drips down and gets everything wet. I promise the humidifiers built in to the ductwork are completely off.

    Have any thoughts about the root cause / how to fix it?

    We had used a portable style dehumidifier, but we are now renting the place out and want a more permanent fix.

    We got an estimate for a "whole house" dehumidifier, but were told it would be too big to fit in the (not tiny) crawlspace where the furnace is located. The estimate calls for a Honeywell TrueDry 65 to be put in the bedroom, which isn't a great solution (noise). The condo unit is under 1000 square feet, how big should the dehumidifier be?

    Another suggestion I got from someone else was to use a "fancy" thermostat that runs the AC unit in the winter as a dehumidifier. Thoughts on this? Danger to the AC unit if the temperatures get to low (snow, ice, etc)? They said I would need to have a low ambient control. Is this a reasonable and safe course of action?

    Lots of questions, thanks for any help!

  2. #2
    Join Date
    Mar 2010
    Location
    Morgan Hill Ca.
    Posts
    1,171
    Has anyone looked into some outside air? Sounds idiotic, but think about it, when that 20 degree air hits the 65-70 degree room it will turn out to be pretty dry...Just a thought. You wont need very much air at all and air quality should get better as well.

    Being as I am not familiar with codes in your area (I'm on the other coast) this would need to be run by a mechanical expert in your neck of the woods.

    Good luck.

    GT
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

  3. #3
    Join Date
    Oct 2006
    Location
    So. NH
    Posts
    740
    Are there working exhaust fans vented to the outside in all the units?

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,062
    Quote Originally Posted by HumidInChicago View Post
    My condo building in chicago is a 4 story, 36 unit building. It was built in 2005. Bricks and concrete. The furnaces are electric furnaces (unusual, I know).

    Many of the units are way too humid in the winter, causing lots of condensation on the windows that drips down and gets everything wet. I promise the humidifiers built in to the ductwork are completely off.

    Have any thoughts about the root cause / how to fix it?

    We had used a portable style dehumidifier, but we are now renting the place out and want a more permanent fix.

    We got an estimate for a "whole house" dehumidifier, but were told it would be too big to fit in the (not tiny) crawlspace where the furnace is located. The estimate calls for a Honeywell TrueDry 65 to be put in the bedroom, which isn't a great solution (noise). The condo unit is under 1000 square feet, how big should the dehumidifier be?

    Another suggestion I got from someone else was to use a "fancy" thermostat that runs the AC unit in the winter as a dehumidifier. Thoughts on this? Danger to the AC unit if the temperatures get to low (snow, ice, etc)? They said I would need to have a low ambient control. Is this a reasonable and safe course of action?

    Lots of questions, thanks for any help!

    Moisture on windows during cold weather is a sign of a lack of fresh air infiltration, excess moistue generation, and/or cold window surfaces. Well built multi-family buildings have little exterior surface area to leak and therefore are typically under-ventilated without mechanical ventilation. There is not enough fresh air to purge indoor pollutants year around. Keep in mind that during cold windy weather, natural infiltration is much more than during calm moderate temp weather. Measuring CO2 levels or moisture content inside the space will confirm the lack of fresh air.
    All occupied space needs a minimum of an air change in 4-5 hours to purge indoor pollutants and renew oxygen. With 1,000 sqft., 50 cfm of fresh air does the job typically. Two occupants in 1,000 sqft. of space adding 1 lb. of moisture per hour get a a 35^F reduction in the inside/outside dew point. More air reduces the inside dew point more. The winter moisture problem is fixed with fresh air ventilation, not a dehumidifier.
    Simple, add fresh dry outside air until the windows stop sweating. This fixes two problems, eliminates you winter moisture problem and dramatically improves your indoor air quality. Reduced pollutants and increased oxygen level are critical for optimum health. Typical indoor odors go away, you sleep better, and generally feel better.
    As outdoor dew points rise in spring and your natural ventilation declines to near zero, your need for mechanical fresh air actually increases during warm calm weather. A sign of adeature air change is the tracking of indoor dew points. The indoor dew points are more than outside depending on the air change rate. Ideal indoor dew points are <55^F which results in 75^,50%RH. As stated above, two adults add 1 lb. per hour moisture. Here is were the dehumidifier comes in, dehumidification is required when the outdoor dew points are +55^F. The a/c will keep the space dry during high cooling loads. 3-4 lbs. per hour dehumidifier is need during low/no cooling loads. The whole house ventilaing dehumidifier, needs a 6" fresh air inlet connected to the outside. Installed correctly, the dehu will blend in the fresh air and circulate it throughout the space.
    The Honeywell or Ultra-Aire whole house dehumidifiers have a optional ventilation option that combines fresh air ventilation, air filtering, and dehumidification into one package. Also you mentioned crawlspace, It is important to cover any earth and close exterior venting to stop infiltrating moistue when the outdoor dew points are high.
    Its worth the extra effort to fit the 65-70 dehumidifier into the space.
    Keep us posted.
    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"

  5. #5
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    +1 ... You likely have a ventilation issue... meaning not enough fresh air, and/or need better exhaust fans in the bathroom and kitchen vent hood. A lot of mdern condos...especially converted commerical./industrial spaces.. have gone to using spray foam over brick walls and installing fairly tight windows. That makes for a very tight home over a residential stick construction...especailly if you have just 1 or 2 outside walls. Additonally spaces <1500sqft (typcial for condo) have the same occupancy as a larger home, but have less volume and air leaksage, so they get humid fast.

    I'd start with looking at your exhaust fans sicne adding fresh air may not be simple. You could get a newer exhaust fan that run continously at low speed, then speeds up usign a swithc or with a motion sensor (when occupied). Panasonic makes some of these. Not cheap, but very low energy consumption. Next option is to add ventilation to your HVAC system somehow. Even better is a whole house dehumidifier mentoned above, but they aren't cheap.... but will save you energy year round and make the space much more comfortable.


    To run an AC below 50F, it needs to have a low ambient kit installed unless it's a higher end unit (not liekly in a condo) like a Carrier Infinity and has low ambient operation standard sicne it has additonal electronic controls integrated in it. A low ambient kit usually just cycles the condenser fan based on refrigerant pressure. Additonally, run times liekly won;t be long enough ot remove much humidity. You'll get the coil wet, then it will jsut reevaporate.

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