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Thread: Ultra-Aire sizing and return configuration

  1. #1
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    Ultra-Aire sizing and return configuration

    Reaching out for some advice about revamping our existing HVAC equipment and adding some dedicated dehumidification/outdoor air supply.

    Replacing two existing hvac systems supplying the first floor/basement and second floor of our house.

    First floor and basement are both 2,900 sqft, with 1,600 sqft of the basement finished. Second floor is 1900 sqft.

    Leaning towards using the Bosch IDS 2.0 gear and would like to add an Ultra-Aire unit to the first floor/basement system. The second floor system is in a closet that's pretty tight and doesn't have room for a dehumidifier.

    Unfortunately, don't have a blower door test/manual J to share. Have yet to stumble upon a local contractor who makes it their practice to size equipment based on this data.

    Located in Kansas City. House was built in 2006 and "seems" moderately tight, but with quite a bit of glass, including some commercial units that could be tighter.

    The contractor who has quoted the new equipment recommends the Ultra-Aire 98h for our application. The Santa Fe website suggest this would be undersized. Any thoughts about who's right?

    Would be easier to tie the Ultra-Aire return duct into the existing HVAC return, rather than reconfigure a dedicated return. As I understand it, the fan on this Bosch equipment runs continuously. Would it significantly compromise the performance of the dehumidifier by using the "alternative" vs "recommended" return configuration?

    Any thoughts/advice are very much appreciated.

  2. #2
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    Welcome! I would suggest the Ultra-Aire 120 foe the basement/mainfloor with fresh air and connection to the mainfloor air handler. Ideally, continuous fan "on" low is great and would require a/c fan during all use.

    This would allow injection of dehumidifier air on the supply and return at same area of the a/c supply. Many users desire independent operation of the dehu/fresh air of the a/c blower. This needs a dependent return from the open part of the home and dehu supply to the a/c supply. The UA 120 fan power is needed.

    Thank you for taking on the "training" job to get another contractor on going the ideal indoor air quality and comfort.

    Keep us posted. We are hear to help you through this.

    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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  4. #3
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    Quote Originally Posted by Aharmon View Post

    Reaching out for some advice about revamping our existing HVAC equipment
    and adding some dedicated dehumidification/outdoor air supply.

    Replacing two existing hvac systems supplying the first floor/basement and second floor of our house.

    First floor and basement are both 2,900 sqft,
    with 1,600 sqft of the basement finished. Second floor is 1900 sqft.


    Leaning towards using the Bosch IDS 2.0 gear and would like to
    add an Ultra-Aire unit to the first floor/basement system.
    The second floor system is in a closet that's pretty tight and doesn't have room for a dehumidifier.

    Unfortunately, don't have a blower door test/manual J to share.
    Have yet to stumble upon a local contractor
    who makes it their practice to size equipment based on this data.

    Located in Kansas City.
    House was built in 2006
    and "seems" moderately tight,
    but with quite a bit of glass, including some commercial units that could be tighter.

    The contractor who has quoted the new equipment recommends the Ultra-Aire 98h for our application.
    The Santa Fe website suggest this would be undersized. Any thoughts about who's right?

    Would be easier to tie the Ultra-Aire return duct into the existing HVAC return,
    rather than reconfigure a dedicated return.
    As I understand it, the fan on this Bosch equipment runs continuously.
    Would it significantly compromise the performance of the dehumidifier
    by using the "alternative" vs "recommended" return configuration?

    Any thoughts/advice are very much appreciated.
    Manual J can be performed based on
    your 7,700 Sq Feet BUILDING THERMAL ENVELOPE description.

    Window Specs, areas and orientation are Necessary.
    Detailed Drawings should be provided.
    Existing energy use and costs should be provided.

    My gmail address: racingdan11
    ___ www.mysimplifliedhvac.com

    ________ ASHRAE Climatic Conditions
    Attached Images Attached Images   
    Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities

  5. #4
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    Thread Starter
    Hi Teddy-

    Thanks very much for your advice!

    Our contractor doesn't do many whole house dehumidifiers, so I want to sort out the details in advance.

    What duct material would you recommend for the intake/exhaust and fresh air ducting? Have it in my head that flex ducting is generally inferior to the sheet metal usually used in my part of the world.

    Is there a particular damper system you would recommend for the fresh air intake?

  6. #5
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    Insulated flex duct is recommended from the dehumidifier supply to the a/c supply. This reduces much mechanical vibration and air noise from the dehumidifier. This is 10". The return from the open part of the home to the dehumidifier return can be metal 10". The fresh air from the outside size is usually 6" insulated flex is <10'. +10" to 20' length should be 10" insulated flex to avoid condensation on the surface of the duct during extreme cold weather. If the home is leaky or unoccupied during extended hours, a electric on/off damper is suggested. Also a balancing damper is suggested in the fresh air duct in the duct near the dehumidifier. Flex has the function of avoiding sweating and transferring vibration noise.

    If the unit is installed above living space, a safety pan is also suggest with a a float switch.
    Glad to hear that he has some experience with this type of equipment.

    Looking forward to hearing more about the install and what the Ultra-Aire does for the home.
    Keep posted.

    Regards Teddy Bear


    Ultra-Aire/Santa Fe.com
    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. #6
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    Quote Originally Posted by Aharmon View Post
    Hi Teddy-

    Thanks very much for your advice!

    Our contractor doesn't do many whole house dehumidifiers,
    so I want to sort out the details in advance.

    What duct material would you recommend for the intake/exhaust and fresh air ducting?

    Have it in my head that flex ducting is
    generally inferior to the sheet metal usually used in my part of the world.
    SHEET METAL obviously has better flow characteristics.
    Insulation on sheet metal must be installed near perfect in order to avoid
    SIGNIFICANT CONDENSATION issues in Many situations.

    One dehumiidifier may not be adequate for 7,700 square feet.
    __________________ ______ -- ... COMPLEX ... -- ______

    Ball Park
    { + / - 18%, _ NO window details provided, Infiltration? }

    Conceptual Manual J calc for large 2006 Built residence
    Attached Images Attached Images  
    Attached Images Attached Images
    Last edited by dan sw fl; 05-12-2021 at 08:33 AM.
    Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities

  8. #7
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    Thread Starter
    Would you upsize the exterior fresh air inlet to 10" or keep it at 6"? That's a pretty big hole in the side of the house.

  9. #8
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    Quote Originally Posted by Aharmon View Post
    Would you upsize the exterior fresh air inlet to 10" or keep it at 6"? That's a pretty big hole in the side of the house.
    A 6" fresh air inlet connected to an 8" lengthly ducts will be ok. The issue is pressure drop in a long duct for a fresh air, upsizing the duct to 8" duct gets us the +100 cfm of fresh air needed for this large home.

    As Dan reminds that the latent load at design is 10,000 btus or 10 lbs. of dehumidification per hour. Originally, I suggest an Ultra-Aire 120, If the basement is fully developed with high occupancy, An UA XT150H maybe a better choice. You could proceed with UA120 and add an Ultra-Aire 70H later if needed.

    Keep us posted on any issues.
    Thank you for the support.

    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. #9
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    Thread Starter
    Any reason to be concerned about oversizing it with the XT155H, other than the upfront cost?

    Thanks very much for your help!

  11. #10
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    If you do not mind occasional 55%RH, stick with the UA 120. Either unit is over-sized during light moisture loads. They both have dehumidistats.

    This is not like a/c sizing.

    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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