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  1. #27
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    Quote Originally Posted by cramir View Post
    Teddy, what is the best schedule for fresh air here in north east Florida?

    C
    I would suggest fresh air whenever the home is occupied at an air change in 4-5 hours.
    Keep us posted on your home.
    Regards Teddy Bear
    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"

  2. #28
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    Nov 2017
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    Jacksonville, FL
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    Quote Originally Posted by teddy bear View Post
    I would suggest fresh air whenever the home is occupied at an air change in 4-5 hours.
    Keep us posted on your home.
    Regards Teddy Bear
    Teddy - changed 98h for a xt105h. System has a dedicated return centrally located in House. Supply is connected exactly in the middle of the supply main trunk (not plenum since plenum is not in the middle of the main line.). Dehumidifier is unable to bring RH to 45%... really frustrating because if system can’t get humidity under 50% this time of the year in north Florida, I can’t imagine in the middle of a humid/hot summer. What are your thoughts Teddy?

    Happy thanksgivin-

    C

  3. #29
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    Jun 2003
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    What to expect from a dehumidifier in hour home. During the high cooling loads when your home is being cooled by the a/c, the a/c must be setup to maintain your desired temp/%RH and the dehumidifier should not be operating. Slowing the the air flow through the cooling coil lowers the %RH in the home. An example is 75^F, 50%RH, a 55^F dew point requires the a/c to provide <49^F dew point cooled to the home. Increasing or decreasing the air flow through the cooling coil raises or lowers the dew point of the cool air to the home. Typically 30^F temp split between the return air temp and the coil temp.
    In most homes, +50%cooling cycle should be able to do this.
    During evening hours or rainy days with high outdoor dew points, the a/c will not run enough enough to remove the moisture from the infiltrating/ventilation and occupants. Enter the whole house dehumidifier. The dehumidifier is sized to remove the moisture from outdoor dew points that occur during moderate to low sensible cooling loads and from the occupants. As you dry below 50%RH, the dehu capacity decreases and amount of moisture to be removed increases. 50%RH is a good number.
    The a/c/dehumidifier interaction is commonly misunderstood. A correctly setup a/c will remove remove about 3 lbs. per ton per hour at 75^F, 50%RH, 55^F dew point. A 3 ton a/c should remove 9 lbs. of moisture per hour. During the same condition, the UA XT105H removes 3 lbs. per hour. Total 9 lbs. per hour will handle 150 cfm of 75^F dew points infiltrating fresh air and 6 occupants. Also reducing indoor airs %RH from 60%RH to 47%RH causes the moisture in the materials to slowly move to the air in the home. Could be 500 lbs. of moisture removal to equalize. Give is all a chance.
    Dehumidifiers set to maintain dew points below the a/c's dew point, reduce or stop the a/c from participating in the home's moisture removal. Then the dehu must be sized to remove all of moisture. Bigger dehumidifiers and much higher energy use is the result.
    If this is confusing, more explanation is required from us.
    Post confusing issues.
    Regards Teddy Bear
    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"

  4. #30
    Join Date
    Nov 2017
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    Jacksonville, FL
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    Quote Originally Posted by teddy bear View Post
    What to expect from a dehumidifier in hour home. During the high cooling loads when your home is being cooled by the a/c, the a/c must be setup to maintain your desired temp/%RH and the dehumidifier should not be operating. Slowing the the air flow through the cooling coil lowers the %RH in the home. An example is 75^F, 50%RH, a 55^F dew point requires the a/c to provide <49^F dew point cooled to the home. Increasing or decreasing the air flow through the cooling coil raises or lowers the dew point of the cool air to the home. Typically 30^F temp split between the return air temp and the coil temp.
    In most homes, +50%cooling cycle should be able to do this.
    During evening hours or rainy days with high outdoor dew points, the a/c will not run enough enough to remove the moisture from the infiltrating/ventilation and occupants. Enter the whole house dehumidifier. The dehumidifier is sized to remove the moisture from outdoor dew points that occur during moderate to low sensible cooling loads and from the occupants. As you dry below 50%RH, the dehu capacity decreases and amount of moisture to be removed increases. 50%RH is a good number.
    The a/c/dehumidifier interaction is commonly misunderstood. A correctly setup a/c will remove remove about 3 lbs. per ton per hour at 75^F, 50%RH, 55^F dew point. A 3 ton a/c should remove 9 lbs. of moisture per hour. During the same condition, the UA XT105H removes 3 lbs. per hour. Total 9 lbs. per hour will handle 150 cfm of 75^F dew points infiltrating fresh air and 6 occupants. Also reducing indoor airs %RH from 60%RH to 47%RH causes the moisture in the materials to slowly move to the air in the home. Could be 500 lbs. of moisture removal to equalize. Give is all a chance.
    Dehumidifiers set to maintain dew points below the a/c's dew point, reduce or stop the a/c from participating in the home's moisture removal. Then the dehu must be sized to remove all of moisture. Bigger dehumidifiers and much higher energy use is the result.
    If this is confusing, more explanation is required from us.
    Post confusing issues.
    Regards Teddy Bear
    Teddy - I see that ideal RH is 50%. My dehu struggles to get there with semi-dry outside conditions. Damp summer will be hard to dry up the house. I feel like if I want to have the house at 45% (even though you think 50 is ideal) I should be able to lower it to that point. Is it possible I’m just undersized? Again, my house is a 2200sq ft 1938 house with spray foam insulation. It is off grade with no insulation on the floor joists. Also, went from a 98h to the 105 and having same issue.

    C

  5. #31
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    Jun 2003
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    Quote Originally Posted by cramir View Post
    Teddy - I see that ideal RH is 50%. My dehu struggles to get there with semi-dry outside conditions. Damp summer will be hard to dry up the house. I feel like if I want to have the house at 45% (even though you think 50 is ideal) I should be able to lower it to that point. Is it possible I’m just undersized? Again, my house is a 2200sq ft 1938 house with spray foam insulation. It is off grade with no insulation on the floor joists. Also, went from a 98h to the 105 and having same issue.

    C
    What does off grade mean? Is that like crawlspace? How many lbs. or gals. of moisture is the dehu removing per hour at what temperature?
    The moisture level of the home is determined by the amount of outside air passing through the home at a specific dew point minus the moisture removed by a/c and dehumidification.

    I agree that a 100 pint per day dehumidifier will keep most homes <50%RH. Yet it depends on the amount of air passing through the home at what dew point and what is the dew point you want in the home.
    If you are talking 75^F, 50%RH is 55^F dew point. When the dew point outside is 50^F, there is no moisture load from the air passing through the home. Than the moisture load is from occupants or could from fish tanks or crawlspace earth.
    How much moisture is removed by the dehu? This tells us if the dehu is working properly.
    Your dehu is rated at 4 lbs. per hour at 80^F, 60% RH, 65^F dew point. As the temp/%RH/dew point decline, so does the capacity of the dehu.
    If you home is air tight with out moisture from other sources, expect <50%RH even during summer high heat and high dew point. I keep my Cape Coral home <55%RH throughout the summer with only the Ultra-Aire 98H. But the temperature inside the home goes up to +85^F during the heat of the day. 85^F, 50%RH is 65^F dew point. The outdoor dew points get up to 75^F during the summer. This a 10^ F reduction is dew point in side the home. Removing 4 lbs. per hour works.
    I need more info from you to comment on how your dehu is working.
    Regards Teddy Bear
    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"

  6. #32
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    Jun 2003
    Location
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    Basement home is FL has me concerned. Any exposed earth or open vents in this basement? Crictical to limit fresh air to an air change in 4-5 hours and any earth or wet spots must be covered with plastic. Also foam on a roof deck with a vented attic could be a problem.
    Also there have been several cases of moisture loading of the foam insulation on the bottom of roof decks.
    Also air leaking in or out of a/c ducts causes excess air movement through a home. Air movement causes high %RH when the outdoor dew points are high. Low %RH in the home when the dew points are <50^F outside.
    Take inside dew points verses outdoor dew point for a conformation of the effect.
    Your dehumidifier and a/c have limitations.
    Your early comments about 60-70%RH during peak summer cooling loads are an indication severe a/c system or air leakage problems.
    Your a/c and air leakage must be controlled to get you to 47%RH during high cooling loads. Than your dehumidifier will maintain the same %RH during evenings and cool wet weather.
    Keep us posted.
    I am really concerned.
    Regards Teddy Bear
    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"

  7. #33
    Join Date
    Nov 2017
    Location
    Jacksonville, FL
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    Quote Originally Posted by teddy bear View Post
    Basement home is FL has me concerned. Any exposed earth or open vents in this basement? Crictical to limit fresh air to an air change in 4-5 hours and any earth or wet spots must be covered with plastic. Also foam on a roof deck with a vented attic could be a problem.
    Also there have been several cases of moisture loading of the foam insulation on the bottom of roof decks.
    Also air leaking in or out of a/c ducts causes excess air movement through a home. Air movement causes high %RH when the outdoor dew points are high. Low %RH in the home when the dew points are <50^F outside.
    Take inside dew points verses outdoor dew point for a conformation of the effect.
    Your dehumidifier and a/c have limitations.
    Your early comments about 60-70%RH during peak summer cooling loads are an indication severe a/c system or air leakage problems.
    Your a/c and air leakage must be controlled to get you to 47%RH during high cooling loads. Than your dehumidifier will maintain the same %RH during evenings and cool wet weather.
    Keep us posted.
    I am really concerned.
    Regards Teddy Bear
    Teddy - I am as concerned as you are. I have a crawlspace that is not encapsulated. It is just dirt (exposed earth) and debris from renovations from the lifetime of the house. Air handler, air ducts and dehumidifier are located in the crawlspace. The main reason of me adding this dehumidifier was for me to keep living space dry to avoid attic to be humid. I sprayed foam the attic (roof deck) and enclosed it with no vents. After this was done, humidity in the attic during the summer was 82%RH. I brought a portable dehumidifier and ran it in the middle of the house. I came to the conclusion that as long as I keep living space dry, attic with no be as humid.

    I ran a blower door test and the results were pretty poor. The blower door(BD) scored 11.2 air changes per hour at 50 pascals (ACH50).

    Air ducts are new from this summer so I am assuming air leaks are minimal.

    C

  8. #34
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    Jun 2003
    Location
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    Now we getting someplace.
    Here is a quick and dirty fix.
    Remove the debris. Level the dirt as best you can. Cover the earth with heavy plastic or a blue plastic tarp cut fit to the walls. Get the vapor barrier to lay tight to the earth with some gravel. Seal all the outside vents.
    Stand back and watch the magic.
    You may still have to setup the a/c to maintain <50%RH during the high cooling loads with the help of the dehumidifier.
    You may choose a professional crawlspace sealing after this is over.
    Thank you figuring out the problem. I was really concerned with results of using on a world class dehumidifier.
    Keep us posted.
    Regards Teddy Bear
    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"

  9. #35
    Join Date
    Nov 2017
    Location
    Jacksonville, FL
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    Quote Originally Posted by teddy bear View Post
    Now we getting someplace.
    Here is a quick and dirty fix.
    Remove the debris. Level the dirt as best you can. Cover the earth with heavy plastic or a blue plastic tarp cut fit to the walls. Get the vapor barrier to lay tight to the earth with some gravel. Seal all the outside vents.
    Stand back and watch the magic.
    You may still have to setup the a/c to maintain <50%RH during the high cooling loads with the help of the dehumidifier.
    You may choose a professional crawlspace sealing after this is over.
    Thank you figuring out the problem. I was really concerned with results of using on a world class dehumidifier.
    Keep us posted.
    Regards Teddy Bear
    Well, now I’m going to have to save for the encapsulation and hope that that is the issue. Would hate to spend that $ and keep having the issue. Thanks for all your help and support, Teddy.

    Happy holidays

    C

  10. #36
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    Jun 2003
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    Madison, WI/Cape Coral, FL
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    I forgot to mention the fact that exposed earth in a crawlspace may evaporate 2-3 lbs. per hour per 1,000 sq.ft. exposed earth when trying to maintain 50%RH above the earth.
    Removing debris and laying down plastic tarp plus sealing vents should be inexpensive to start with.
    Keep us posted.
    Regards Teddy Bear
    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"

  11. #37
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    Nov 2017
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    Jacksonville, FL
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    Quote Originally Posted by teddy bear View Post
    I forgot to mention the fact that exposed earth in a crawlspace may evaporate 2-3 lbs. per hour per 1,000 sq.ft. exposed earth when trying to maintain 50%RH above the earth.
    Removing debris and laying down plastic tarp plus sealing vents should be inexpensive to start with.
    Keep us posted.
    Regards Teddy Bear
    What would be a difference between that and a full on encapsulating. I have a quote for 5k to encapsulate the crawkspace. Do you think humidity in attic is coming from crawlspace or a poor insulation install?

    C

  12. #38
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    Quote Originally Posted by cramir View Post
    What would be a difference between that and a full on encapsulating. I have a quote for 5k to encapsulate the crawkspace. Do you think humidity in attic is coming from crawlspace or a poor insulation install?

    C
    Every sq.ft. of plastic covered earth decrease the amount of moisture that you must deal with. The full Monty is impressive.
    I would expect 75% effectiveness.
    Attic is another question. Your roofing material is the start. Metal or ice/rain shied stop all moisture from outside. Sun and condensation drive moisture through most other roofing materials. These slow steady moisture movement shows up in the attic space when the sun heats the roof. Over-night, the moisture condenses at the cool roof deck. The amount of moisture in the home also plays a role.
    If excess moisture builds up in the attic, dehumidification or trickle attic peak ventilation will solve the problem.
    Get control of your %RH in your and monitor the attic. Go from there.
    Attics are tougher than crawlspaces.
    Keep us posted.
    Regards Teddy Bear
    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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