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Thread: Sizing A/C and ERV for my house

  1. #1
    Join Date
    Jan 2010
    Location
    Oklahoma City
    Posts
    171
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    Sizing A/C and ERV for my house

    Me: about 10 years working off and on Commercial A/C over 4 decades 6 years in this decade for Lennox (I know heard all the issues with them don't want to go there) so no install and no residential experience. Not doing HVAC now but building my retirement house.

    House: We are building with SIP panels in Oklahoma. 1/2" OSB on both sides glued to 6" foam for walls and 8.5" foam for roof. all joints are foamed and taped. I will tape joints and use a spray sealer on outside that is a water seal but allows vapor to go out according to my designer. The air infiltration is almost zero so I will need fresh air intake so using an ERV makes sense. I have worked on the big ERV units for big box stores but not the residential stuff.
    2730 Sq Ft ranch with 10 ft ceiling and 1000 sq ft of that will have cathedral ceilings peak at 15ft.

    On sip houses they recommend down sizing from normal requirements to 60% of what you would normally use.

    Questions:
    Where should I go for A/C load calculations for this type house?
    is the ASHRAE 62.2 fresh air guide (about 100 cfm) enough for an air tight house?
    Plan is to pull air from bathrooms and fresh air to bedrooms and living area. Does this sound right?
    What am I missing?

    Thanks for your time

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    10,598
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    Good plan. Suggest icing on the cake, a small whole house dehumidifier like the the Ultra-Aire 120 t maintain <50%rH during evenings and rainy days with high outdoor dew points which are common in "green grass" climates like OK.

    The Ultra-Aire is a high efficiency dehu with a merv 13 air filter that can be connected to the ERV and A/C.

    Ultra air will maintain low %RH by removing upto 5 lbs. of moisture per hour.

    Interested in hearing from you about details and interest.

    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
    Nov 2004
    Location
    SW FL
    Posts
    11,556
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    RESIDENTIAL HVAC DESIGN PROCESS _ Figure 3

    Quote Originally Posted by Retread View Post
    Me: about 10 years working off and on Commercial A/C over 4 decades 6 years in this decade for Lennox (I know heard all the issues with them don't want to go there) so no install and no residential experience.
    Not doing HVAC now but building my retirement house.

    House: We are building with SIP panels in Oklahoma.
    1/2" OSB on both sides glued to 6" foam for walls and 8.5" foam for roof.

    All joints are foamed and taped.
    I will tape joints and use a spray sealer on outside that is a water seal but allows vapor to go out according to my designer.
    The air infiltration is almost zero so I will need fresh air intake so using an ERV makes sense.

    I have worked on the big ERV units for big box stores but not the residential stuff.

    2730 Sq Ft ranch with 10 ft ceiling and
    1000 sq ft of that will have cathedral ceilings peak at 15ft.

    On sip houses they recommend down sizing from normal requirements to
    60% of what you would normally use. __ Use ACCA Manual J ROOM-BY-ROOM Load Calculation

    Questions:
    Where should I go for A/C load calculations for this type house?

    Is the ASHRAE 62.2 fresh air guide (about 100 cfm) enough for an air tight house?
    Plan is to pull air from bathrooms and fresh air to bedrooms and living area.
    Does this sound right?
    _________ Yes, I might design for ~ 150 CFM & operate it ~ 2/3rds of the time.
    _________________ Fresh Air can be provided in the HVAC Supply Ductwork, IF you are using a conventional air distribution system.
    _______________ Use UltraAire model 120
    Your NEW Construction project is my favorite structure/BUILDING THERMAL ENVELOPE
    to develop an effective and economical Residential HVAC System design.

    Your Heat Gains and Heat Losses should be VERY Low
    Pat attention to detail on Cathedral Ceiling insulation.

    ____ Personalized, Custom Service
    _________ www.mysimplifiedhvac.com __ 5 Pages
    xx
    https://www.rses.org/assets/servicea...al/630-148.pdf

    Alternates:
    1. Multi-Split System(s)
    2. Hybrid (Heat Pump & Furnace) System
    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

  4. #4
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    11,556
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    ___ 19.3'F Winter
    ___ 99.5'F Summer
    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. #5
    Join Date
    Nov 2006
    Location
    Athens, Ohio
    Posts
    8,886
    Post Likes
    You may want to investigate the CERV2 by Build Equinox. It is a ventilator with a small compressor to heat or cool the incoming air, not just exchange heat as most ventilators do.
    I have not used one nor installed one as our area does not have many passive or net-zero homes. I did ask about prices - YES they are expensive but this may be just what you need.
    *********
    https://www.hvac20.com/ High efficiency equipment alone does not provide home comfort and efficiency. HVAC2.0 is a process for finding the real needs of the house and the occupants. Offer the customer a menu of work to address their problems and give them a probability of success.

    Find contractors with specialized training in combustion analysis, residential system performance, air flow, and duct optimization https://www.myhomecomfort.org/


    Site member map HERE!

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