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  1. #1
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    Ultra-aire 98h install question

    Hi folks, trying to get my rh down in my house. With the AC running I'm still between 60-70 RH. Decided to purchase the 98h. I'm planning my install in my basement and want to make sure I purchase all necessary supplies.

    Unfortunately there is no viable option to install a dedicated return for the dehu.
    My plan is to tap into the return and supply plenums and hang the unit adjacent to the air handler. Install option in the middle of page 12 of the manual for reference.

    My goal is to have the air handler NOT required to run with the dehu running. I understand I need a 10" round backdraft damper in the duct prior to feeding the supply.

    My question surrounds the "check damper" between the return duct feeding the dehu and the air handler. Should this be a motorized damper such as the Honeywell ZD10X20TZ? Is there a way to wire it so that it is normally closed? And opens when the air handler fan kicks in?

    Or is there a different type of damper I should use? The plenum is 10x20.

    The dehu will be controlled by an ecobee4.
    My plan is to add a fresh air duct with motorized damper wired to a wemo switch/and relay. This will be phase two of the project, want to get the humidity in the house down first.

    Thanks in advance!

  2. #2
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    Jun 2003
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    Quote Originally Posted by trip1050 View Post
    Hi folks, trying to get my rh down in my house. With the AC running I'm still between 60-70 RH. Decided to purchase the 98h. I'm planning my install in my basement and want to make sure I purchase all necessary supplies.

    Unfortunately there is no viable option to install a dedicated return for the dehu.
    My plan is to tap into the return and supply plenums and hang the unit adjacent to the air handler. Install option in the middle of page 12 of the manual for reference.

    My goal is to have the air handler NOT required to run with the dehu running. I understand I need a 10" round backdraft damper in the duct prior to feeding the supply.

    My question surrounds the "check damper" between the return duct feeding the dehu and the air handler. Should this be a motorized damper such as the Honeywell ZD10X20TZ? Is there a way to wire it so that it is normally closed? And opens when the air handler fan kicks in?

    Or is there a different type of damper I should use? The plenum is 10x20.

    The dehu will be controlled by an ecobee4.
    My plan is to add a fresh air duct with motorized damper wired to a wemo switch/and relay. This will be phase two of the project, want to get the humidity in the house down first.

    Thanks in advance!
    Thanks for the chance to serve. I am concerned about your comment about "60-70%RH" while cooling. Any time your a/c operates for an hour or more steady, your a/c should be able to get to the target %RH. 50%RH is a good target. During long cooling runs, a properly setup a/c should remove enough moisture to dry the home. If not, check the supply air temperature/%RH for <50^F dew point. It is important to efficient humidity control during high cooling loads. Usually the blower is moving too much air through the cooling coil and must be slowed to allow a colder coil temperature. A colder a/c coil removes more moisture like 3 lbs. of moisture per ton. You will still need the dehumidifier for low/no cooling runs and high outdoor dew points to remove 2-4 lbs. of moisture per hour.

    Back to your install questions. Is the basement open to the main floor of the home? If yes, suggest connecting the return of the dehumidifier to the return of the a/c. Blow the dry air from the dehumidifier to the basement developed area. This avoids any check dampers or need to operate the a/c blower while dehumidifier runs. This also focuses the drying of the dehumidifier to the basement which is much cooler. Even a 1" basement door under cut may be enough of a basement to the mainfloor return to the open part of the home.
    I would start by checking the a/c for proper setup and operating the dehumidifier just on the basement while monitoring the %RH in both spaces. The basement will drop to <50%RH with significant impact on the mainfloor. Next connect the return of the dehumidifier to the a/c return. Pressurizing the basement with air from the mainfloor that will infiltrate the main floor through basement door undercut and other leaks. The dry air from the dehumidifier will find its way back to the a/c duct system. This will get you the air movement for humidity control and fresh air circulation.

    Also avoid blowing the dry air from the dehumidifier into the a/c return. The warm dry air from the dehumidifier decreases the moisture removed by the a/c when both operate.
    This was the original method of install the dehumidifiers for years. I do this in my own basement home. Basements are usually too cool.
    Give me feed back on the temp/%RH supply/return of your a/c. Where is this home?
    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"

  3. #3
    Join Date
    Jun 2017
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    Thread Starter
    Happy Fourth All!

    My apologies for the radio silence on this one, been dealing with painters, flooring guys and unpacking a sea of boxes. Finally getting back to this project.

    To answer TBs questions, I actually have a better baseline of the AC performance, when running AC to keep the house at 72, the RH is actually down in the high 40's to mid 50's. Before I had set the fan constant to run 24/7 (help paint and floor finish dry). I wasn't really tracking when or how log the compressor was turning on and cooling.

    I currently have the 98H hung and condensate line installed. I'm waiting on some fittings to arrive before I tap into existing HVAC. The basement is connected, and there are enough openings to allow adequate are movement. I will pull from the return and dump into the open basement as TB suggested.

    My current question involves wiring the 98H. I'm using an ecobee4 to control the dehu and want to make sure I am connecting it properly. If I am reading it right, I will need to connect the Blue (compressor and fan) wire to a 24v output from the ecobee, then either the red or white from the 98H to the common wire I assume for the thermostat/air handler?

    Do I need to hook the yellow transformer wire up to anything in this setup?

    Also, I thought I had the ecobee4 set up correctly, I was testing 25ish volts between the acc+ and the com wire when it was calling for dehumidication, but when i turned the dehu off on the ecobee, I was still getting between 11-12v between the same leads. What am I missing? Shouldn't this go to 0?

    Thanks in advance!

  4. #4
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    Quote Originally Posted by trip1050 View Post
    Happy Fourth All!

    My apologies for the radio silence on this one, been dealing with painters, flooring guys and unpacking a sea of boxes. Finally getting back to this project.

    To answer TBs questions, I actually have a better baseline of the AC performance, when running AC to keep the house at 72, the RH is actually down in the high 40's to mid 50's. Before I had set the fan constant to run 24/7 (help paint and floor finish dry). I wasn't really tracking when or how log the compressor was turning on and cooling.

    I currently have the 98H hung and condensate line installed. I'm waiting on some fittings to arrive before I tap into existing HVAC. The basement is connected, and there are enough openings to allow adequate are movement. I will pull from the return and dump into the open basement as TB suggested.

    My current question involves wiring the 98H. I'm using an ecobee4 to control the dehu and want to make sure I am connecting it properly. If I am reading it right, I will need to connect the Blue (compressor and fan) wire to a 24v output from the ecobee, then either the red or white from the 98H to the common wire I assume for the thermostat/air handler?

    Do I need to hook the yellow transformer wire up to anything in this setup?

    Also, I thought I had the ecobee4 set up correctly, I was testing 25ish volts between the acc+ and the com wire when it was calling for dehumidication, but when i turned the dehu off on the ecobee, I was still getting between 11-12v between the same leads. What am I missing? Shouldn't this go to 0?

    Thanks in advance!
    A/c setup sounds good because you were able to maintain 50%RH with a/c on long runs.
    For control of the dehumidifier, yellow from the dehumidifier to dehu acc 24V , from acc back to blue on the dehumidifier. Can you adjust the dehumidistat dead band, cut in verses cut out, like 4-5%RH differential? This prevents short cycling. Use flex duct around the dehumidifier to limit vibration.
    Not sure of about the goto 0 thing.
    Attaching wiring diagram.
    Again, thanks for the support.
    Keep us posted on humidity levels and overall operation.
    Regards Teddy Bear

    Name:  Ecobee connections.JPG
Views: 488
Size:  35.9 KB
    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
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    Jun 2017
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    Thread Starter
    Thank you!!

    Dehu is running like a champ, well it is off now, Rh was around 65% when it started, now it is down to 47% after about an hour or less, wasn't watching to see when it actually turned off. I just noticed the house is much more comfortable and was reminded to check the levels. Wife noticed it as well.

    Yes, I have the ecobee set for a 5% delta to prevent short cycling. Currently target RH is set at 46%. In going to watch to see if it kicks back on at 51+%.

    Once I get some time I will work on getting the fresh air intake vent installed. i will probably be back with some wiring questions for the damper and dehu.

    Thanks again!!

  6. #6
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    Quote Originally Posted by teddy bear View Post
    Thanks for the chance to serve. I am concerned about your comment about "60-70%RH" while cooling. Any time your a/c operates for an hour or more steady, your a/c should be able to get to the target %RH. 50%RH is a good target. During long cooling runs, a properly setup a/c should remove enough moisture to dry the home. If not, check the supply air temperature/%RH for <50^F dew point. It is important to efficient humidity control during high cooling loads. Usually the blower is moving too much air through the cooling coil and must be slowed to allow a colder coil temperature. A colder a/c coil removes more moisture like 3 lbs. of moisture per ton. You will still need the dehumidifier for low/no cooling runs and high outdoor dew points to remove 2-4 lbs. of moisture per hour.

    Back to your install questions. Is the basement open to the main floor of the home? If yes, suggest connecting the return of the dehumidifier to the return of the a/c. Blow the dry air from the dehumidifier to the basement developed area. This avoids any check dampers or need to operate the a/c blower while dehumidifier runs. This also focuses the drying of the dehumidifier to the basement which is much cooler. Even a 1" basement door under cut may be enough of a basement to the mainfloor return to the open part of the home.
    I would start by checking the a/c for proper setup and operating the dehumidifier just on the basement while monitoring the %RH in both spaces. The basement will drop to <50%RH with significant impact on the mainfloor. Next connect the return of the dehumidifier to the a/c return. Pressurizing the basement with air from the mainfloor that will infiltrate the main floor through basement door undercut and other leaks. The dry air from the dehumidifier will find its way back to the a/c duct system. This will get you the air movement for humidity control and fresh air circulation.

    Also avoid blowing the dry air from the dehumidifier into the a/c return. The warm dry air from the dehumidifier decreases the moisture removed by the a/c when both operate.
    This was the original method of install the dehumidifiers for years. I do this in my own basement home. Basements are usually too cool.
    Give me feed back on the temp/%RH supply/return of your a/c. Where is this home?
    Keep us posted.
    Regards Teddy Bear
    Hi I have a question on this setup. Will this setup work for finished basement that is also heated from the main furnace supply. I still want fresh air during cold season and would pressurizing basement diminish its heating

  7. #7
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    Quote Originally Posted by senaskuinas View Post
    Hi I have a question on this setup. Will this setup work for finished basement that is also heated from the main furnace supply. I still want fresh air during cold season and would pressurizing basement diminish its heating
    We are talking about a small amount of fresh air like 80-100 cfm blended into 20,000 cf of house air. Your heating system deals with this amount of fresh air whenever the wind blows 10 mph. Also when fresh air is mechanically operated, the amount of fresh air entering the home decreases significantly.
    40,000-60,000 btus of heating from a heat pump or furnace easily deals with this type of normal heating loads.
    Keep us posted on other concerns.
    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"

  8. #8
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    Quote Originally Posted by teddy bear View Post
    We are talking about a small amount of fresh air like 80-100 cfm blended into 20,000 cf of house air. Your heating system deals with this amount of fresh air whenever the wind blows 10 mph. Also when fresh air is mechanically operated, the amount of fresh air entering the home decreases significantly.
    40,000-60,000 btus of heating from a heat pump or furnace easily deals with this type of normal heating loads.
    Keep us posted on other concerns.
    Regards Teddy Bear
    Another question - in this setup can both HVAC and dehu run at the same time and called on independently ? Do I need a gravity damper between HVAC return and dehu return?

  9. #9
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    The a/c and the dehumidifier operate independently, also they can run at the same time.
    Ideally the dehu supply has a check damper when connected to the a/c on the supply side. Normally, the dehumidifier runs mostly when the a/c is in a low/no load condition.
    Again, like to see a setup with dehu drawing air from the open part of the home and dehu supply blowing dry air into the a/c supply. The one limitation is extreme a/c supply pressure. With a/c duct pressures of +.6"WG, avoid operating the dehu when the a/c operates. The Ultra-Aire DEH3000 controller has circuit connected to the a/c to avoid dehu operating when the a/c operates. Normally not a problem.
    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"

  10. #10
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    Quote Originally Posted by teddy bear View Post
    The a/c and the dehumidifier operate independently, also they can run at the same time.
    Ideally the dehu supply has a check damper when connected to the a/c on the supply side. Normally, the dehumidifier runs mostly when the a/c is in a low/no load condition.
    Again, like to see a setup with dehu drawing air from the open part of the home and dehu supply blowing dry air into the a/c supply. The one limitation is extreme a/c supply pressure. With a/c duct pressures of +.6"WG, avoid operating the dehu when the a/c operates. The Ultra-Aire DEH3000 controller has circuit connected to the a/c to avoid dehu operating when the a/c operates. Normally not a problem.
    Keep us posted.
    Regards Teddy Bear
    I really like your advise on connecting return of the dehumidifier to the return of the a/c. and blowing whole dry air from the dehumidifier to the finished basement without connecting it to the a/c supply. My basement is much more humid and colder that the rest of the house. In this scenario the a/c supply pressure is not a problem but how about the a/c return vacuum?

  11. #11
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    Quote Originally Posted by senaskuinas View Post
    I really like your advise on connecting return of the dehumidifier to the return of the a/c. and blowing whole dry air from the dehumidifier to the finished basement without connecting it to the a/c supply. My basement is much more humid and colder that the rest of the house. In this scenario the a/c supply pressure is not a problem but how about the a/c return vacuum?
    With a cold basement in a green grass climate, this is a good strategy. Also this causes circulation of the whole house through the basement back to the home. No problem with drawing air from a/c return with a vacuum. This puts a slight positive pressure on the basement which slows soil gases from entering the basement. Expect several ^F rise which decreases the %RH in the basement about 4%RH alone. Also this is a simple installation. Locate the dehumidistat in the basement space.
    Trying any of these specific concepts are easily changed later.
    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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