Help with my new home HVAC sizing - Page 2
Page 2 of 3 FirstFirst 123 LastLast
Results 14 to 26 of 27
  1. #14
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,810
    Quote Originally Posted by dan sw fl View Post
    I understand ACH=
    _____TIGHT __: 0.15
    SEMI-TIGHT __: 0.26
    _ AVERAGE __: 0.39
    SEMI-Loose __: 0.61
    ___ Loose ___: 0.82

    based on my use of Manual J8 abridged.

    Some residences with foam products ought to be < ~0.2
    Right Dan; I was just using .4 ACH for his situation because his home needs to be above the code minimum home air-changes of 0.35 ACH, when it is properly ventilated.

    Of course, the proper way is to do the blower door test & use the actual lower ACH number so the load-calc would estimate the needed makeup air...then he should use 0.2 or less ACH.

  2. #15
    Join Date
    May 2013
    Posts
    6
    Ok I tried to figure out the Manual J. This doesn't make sense to me. Did I do this right?
    Name:  Manual J.jpg
Views: 43
Size:  47.5 KB
    Attached Images Attached Images  

  3. #16
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,225
    LOOKS like you put in about 900 sq feet of window which seems to be nearly 3 X too much.

    Ceiling is ok.
    Walls are not enough.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  4. #17
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,225
    A GUESSED 12-Minute analysis Version of _Whole House Load Calculator_ is attached
    simply
    knowing 2,900 Square Feet total and walls are foamed.
    Ceiling R-38
    _Walls R-18
    Total Window Area 380 Square Feet

    I would say windows may be ~6,000 BTU/Hr too much for Sensible Load (Heat Gain) if you actually have SHGC < 0.36.

    However, I don't even know how many windows, total glass area, exact orientation, U-value nor SHGC.
    Attached Images Attached Images
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  5. #18
    Join Date
    May 2013
    Posts
    6
    I tried to open you calc, but it says I don't have permission. I tried to redo the calculations. See if this is better. I do have a lot of windows on our southeast wall, and all of them are under a cover patio. I really appreciate all your help.
    Name:  Manual J.jpg
Views: 38
Size:  48.8 KB

  6. #19
    Join Date
    May 2013
    Posts
    6
    Ok, I was able to open it, and it is really different from mine. So bottom line, what does calc recommend for HVAC size and ventilation needs. I know I am stupid when it comes to understanding all this.

  7. #20
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Quote Originally Posted by Cwatts15 View Post
    3 bids- all very different, 1: 2ton & 3ton 80% 13seer Lennox- gas unit with optional ERV, 2: 2ton & 5ton 93% 13seer Armstrong with option fresh air damper. 3: 5ton & mini-split Armstrong.
    Pure speculation without doing a load calculation, but I think it would probably be best if you toss all 3 of those bids in the trash.
    #1 and 3 are the kind of sizing you would see in a stick built house with a questionable thermal envelope in North Texas.
    #2 is just ridiculous.

    In a tight, well insulated 2900 sq ft house, unless you have some really big unshaded west windows,I'd be skeptical of anything that came out to more than 3 tons + ERV for the main part of the house, and a minisplit for the master bedroom.
    If you do have really big unshaded west facing windows, a conventional system will always struggle to evenly heat and cool the home due to its load diversity.
    Applications where there is high load diversity is where systems like a Daikin VRVIII-S really shine.
    If more government is the answer, then it's a really stupid question.

  8. #21
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,225
    Quote Originally Posted by Cwatts15 View Post
    Ok, I was able to open it, and it is really different from mine.

    So bottom line, what does calc recommend for HVAC size and ventilation needs.
    I don't even know how many windows, total glass area, exact orientation, U-value nor SHGC.

    I wouldn't make a Specific design recommendation without drawings, specs and
    frequent field checks on adherence to building thermal envelope specs.

    I would use an ERV at about 150 CFM with intermittent timed operation.
    ... 1/3 to 1/2 the time.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  9. #22
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,225
    Quote Originally Posted by Cwatts15 View Post
    I tried to open you calc, but it says I don't have permission.
    I tried to redo the calculations. See if this is better.
    I do have a lot of windows on our southeast wall, and all of them are under a cover patio.
    620 Square Feet of Glass would be typical of a 6,000 Square Foot McMansion in FL or ...
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  10. #23
    Join Date
    May 2013
    Posts
    6
    Ohhh, this is crazy. I have 21 windows 7 of which are little square ones and 2 are 1x5 in bathrooms. I thought my windows were about 325sqft or so. I do have 3 large sliding doors on the SE (backside of house) that are under covered patio. Only 3 - 4x5 windows, and 4 - 2 x 1.6 windows facing SW or NW.
    We are will have foam walls, but not foaming the roof. That will be blown cellulose with radiate barrier sheathing. We are getting pretty good windows-energy-star approved. I have tried my best to give you the correct info. I guess that's why I am a nurse practitioner and not into HVAC. But I am sure trying to understand it all.

  11. #24
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Quote Originally Posted by Cwatts15 View Post
    We are will have foam walls, but not foaming the roof.
    Why not?
    If more government is the answer, then it's a really stupid question.

  12. #25
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,250
    It'd probably be more bang for your buck to spray foam roof deck and use traditional insulation in walls, especially if any ductwork will be in the attic.

  13. #26
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,225
    Quote Originally Posted by Cwatts15 View Post

    Ohhh, this is crazy.
    I have 21 windows

    7 of which are little square ones and
    2 are 1x5 in bathrooms.

    I thought my windows were about 325 sq ft or so.

    I do have 3 large sliding doors on the SE (backside of house) that are under covered patio.
    Only
    3 - 4x5 windows, and
    4 - 2 x 1.6 windows facing SW or NW.

    We are will have foam walls, but not foaming the roof. That will be blown cellulose with radiate barrier sheathing.
    We are getting pretty good windows-energy-star approved. I have tried my best to give you the correct info.

    I guess that's why I am a nurse practitioner and not into HVAC.
    But I am sure trying to understand it all.
    How will the house be built without drawings?

    Window Identification
    7 little ones _____ 20 sq feet
    2 1 x 5 _________ 10
    3 4 x 5 _________ 60
    4 2x1.6_________ 13

    16 Windows _____ 103
    5 unknown

    3 Large Sliding Doors
    10 x 8 ________ 240
    --------------------------------------------------------------------------------
    I guess _large_ is somewhere between 6 x 8 up to 22 x 10, and I have seen that
    and anywhere in this range.
    Including 20 x 10 retractable wall at right angle to another 20 x 10
    forming a " disappearing double wall'
    opening to about a 4,000 square foot deck.

    So, crazy is all relative.
    -----------------------------------------
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

Page 2 of 3 FirstFirst 123 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event