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  1. #1
    Join Date
    Nov 2010
    Posts
    145

    Does this Load Calc sound correct- Sizing Question?

    Hi gents.

    Do these load calculations look right.... and since I have a two story with two large stairwells allowing substantial heat rise/cool air descend... should I make any adjustment for that in sizing?

    I have completed two load calculations using HVAC-Calc (Sleeth program) for my 1985 construction 2 story plus unheated basement. One for each system: main floor and unconditioned basement and 2nd floor.

    Traditional 2 story, 1200 SF main floor + 70 SF of stairwell plus 300 SF of cantilevered sunroom with lots of glass, 2 skylights and cathedral ceiling= almost half the losses and gains on the 1st floor. Windows are double thermo pane. I assume R11 in the walls, measure 8 inches or R26 in the attic (2nd floor load).
    Floors are all hardwood, no insulation above the basement. Basement is 2 sides completely below grade, one side is half below grade, and back wall is studs with r11 insulation but only 3/16 inch pseudo wood paneling. I assumed only 2 people... on the main floor. Should I include more... I have seen 2 persons per bedroom but ???? I have had up to 75 people in parties.... usually during heating period.. but what about a summer party? 50 people can double the AC load.


    Design temp Atlanta GA winter 21 summer 95. Inside W 72 S 75

    Don Sleeth, author, suggests doing load with basement as conditioned even though it isnt... to reflect significant losses? When I drop out the basement completely and change the floor to "over unheated basement" it drops about 6k BTU off the heat load. Don also suggests upsizing the heat by 20-25%, but that as much as any will be a function of what sizes are available. My 49k would be80% of 60k.

    1st floor: 2770 SF (1500 main floor and 1200 basement) Total gain: 36k (3T), loss 49k.

    2nd floor: 1626 SF (1200 plus 225 of bonus room over unheated garage, outside air on three sides with two gables... plus heated and cooled stairwell over ceiling/roof combo) .... 21k Air ... 28k furnace. These just seem a little low, especially air, which has the heat rising from downstairs through the two stairwells.

    At any rate, I would greatly appreciate your thoughts if these sound right for a pretty standard builder grade 2 story traditional home.

    Glad I learned of HVAC-TALK so that at least this time I could do or obtain a load calc and right size my equipment, unlike my experience in 2009 with no fewer than 3 contractors not even breathing a word about sizing other than to "match" what came out of a 1956 home that was built with no insulation at all.

    Thanks in advance, Paul

  2. #2
    Join Date
    Nov 2010
    Posts
    145

    No comments? Am I making sense? Enough info?

    Bump to top. So no clarity from the experts?

    Thanks, Paul

    Quote Originally Posted by shovel99 View Post
    Hi gents.

    Do these load calculations look right.... and since I have a two story with two large stairwells allowing substantial heat rise/cool air descend... should I make any adjustment for that in sizing?

    I have completed two load calculations using HVAC-Calc (Sleeth program) for my 1985 construction 2 story plus unheated basement. One for each system: main floor and unconditioned basement and 2nd floor.

    Traditional 2 story, 1200 SF main floor + 70 SF of stairwell plus 300 SF of cantilevered sunroom with lots of glass, 2 skylights and cathedral ceiling= almost half the losses and gains on the 1st floor. Windows are double thermo pane. I assume R11 in the walls, measure 8 inches or R26 in the attic (2nd floor load).
    Floors are all hardwood, no insulation above the basement. Basement is 2 sides completely below grade, one side is half below grade, and back wall is studs with r11 insulation but only 3/16 inch pseudo wood paneling. I assumed only 2 people... on the main floor. Should I include more... I have seen 2 persons per bedroom but ???? I have had up to 75 people in parties.... usually during heating period.. but what about a summer party? 50 people can double the AC load.


    Design temp Atlanta GA winter 21 summer 95. Inside W 72 S 75

    Don Sleeth, author, suggests doing load with basement as conditioned even though it isnt... to reflect significant losses? When I drop out the basement completely and change the floor to "over unheated basement" it drops about 6k BTU off the heat load. Don also suggests upsizing the heat by 20-25%, but that as much as any will be a function of what sizes are available. My 49k would be80% of 60k.

    1st floor: 2770 SF (1500 main floor and 1200 basement) Total gain: 36k (3T), loss 49k.

    2nd floor: 1626 SF (1200 plus 225 of bonus room over unheated garage, outside air on three sides with two gables... plus heated and cooled stairwell over ceiling/roof combo) .... 21k Air ... 28k furnace. These just seem a little low, especially air, which has the heat rising from downstairs through the two stairwells.

    At any rate, I would greatly appreciate your thoughts if these sound right for a pretty standard builder grade 2 story traditional home.

    Glad I learned of HVAC-TALK so that at least this time I could do or obtain a load calc and right size my equipment, unlike my experience in 2009 with no fewer than 3 contractors not even breathing a word about sizing other than to "match" what came out of a 1956 home that was built with no insulation at all.

    Thanks in advance, Paul

  3. #3
    Join Date
    Dec 2002
    Location
    Arizona
    Posts
    4,368
    I assumed only 2 people... on the main floor. Should I include more... I have seen 2 persons per bedroom but ???? I have had up to 75 people in parties.... usually during heating period.. but what about a summer party? 50 people can double the AC load.
    Number of bedrooms plus one is the correct people load. Don't be sizing for parties you have two times a year for a few hours!
    Make your expertise uniquely valuable.

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  4. #4
    Join Date
    Nov 2010
    Posts
    145

    Thanks!

    Quote Originally Posted by jimj View Post
    Number of bedrooms plus one is the correct people load. Don't be sizing for parties you have two times a year for a few hours!

    Thanks Jim.

  5. #5
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,273
    ___ VERY DIFFICULT to address even ONE of these,
    ... ... Five in combination: one better have experience and time
    ... ... to address the complexity.
    1. Stairwell
    2. 300 SF of cantilevered Sunroom with lots of glass,
    3. 2 skylights
    4. Cathedral ceiling
    5. ROOM Above Garage

    THIS CONFIGURATION SEEMS TO BE _FAR FROM A STANDARD BUILDER GRADE_ TWO STORY.

    To give a REALISTIC estimate I would have to study real DETAILED plans, Specs and duct work
    for about 5 hours to say if sizing and air distribution were adequate.

    AND I am normally willing to give an approximation.
    I really wonder about 21,000 BTU/Hr upstairs and air distribution.

    Any summer party > 83'F and > 20 people and you will likely have to get additional temporary cooling.
    _ Spot Cooler rental
    OR stick to Spring, Fall or Winter parties.

    http://www.harrisdiversifiedllc.com/...togallery.html

    MOVINCOOL
    http://www.americanspotcooling.com/a...ling,_Atlanta/
    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

  6. #6
    Join Date
    Nov 2010
    Posts
    145
    Thanks Dan. You have explained why I am not getting other responses. Lots of moving parts. I will continue to check the 2nd floor calcs. Most immediate need is the system on the main floor 28/11 years old. Paul



    Quote Originally Posted by dan sw fl View Post
    ___ VERY DIFFICULT to address even ONE of these,
    ... ... Five in combination: one better have experience and time
    ... ... to address the complexity.
    1. Stairwell
    2. 300 SF of cantilevered Sunroom with lots of glass,
    3. 2 skylights
    4. Cathedral ceiling
    5. ROOM Above Garage

    THIS CONFIGURATION SEEMS TO BE _FAR FROM A STANDARD BUILDER GRADE_ TWO STORY.

    To give a REALISTIC estimate I would have to study real DETAILED plans, Specs and duct work
    for about 5 hours to say if sizing and air distribution were adequate.

    AND I am normally willing to give an approximation.
    I really wonder about 21,000 BTU/Hr upstairs and air distribution.

    Any summer party > 83'F and > 20 people and you will likely have to get additional temporary cooling.
    _ Spot Cooler rental
    OR stick to Spring, Fall or Winter parties.

    http://www.harrisdiversifiedllc.com/...togallery.html

    MOVINCOOL
    http://www.americanspotcooling.com/a...ling,_Atlanta/

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