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  1. #14
    Join Date
    Apr 2004
    Posts
    7,680
    I forgot to put blinds in the south windows ...Duh... they are bedrooms so I put min blinds at and the sensible drops to 19284 at 1000 cfm whcih knock the unit down to 2.5 ton.

    I also have a 1.5' overhang with the windows 1' down from the top. This gives all the glass a total of 4627 gain in cooling

    [Edited by docholiday on 06-24-2005 at 09:06 AM]

  2. #15
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    just how much is the vault? ie= how much extra height 1.5ft?

    5 people for 3bdrm? Thought the criteria was 2 in master, 1 for each other bdrm --

    no slab loss for a/c in TX? seems to me that it was 17% for Habitat House here in Huntsville AL. ~1000sf.

    HO: for long range, plant some trees! put film on windows, solar screens, trellis shading windows & door to west & south -- vines on trellis -- could be grapes.

    Yesterday it was 92F here, got to 74 in my kit on 2nd level of trilevel -- one 5000 btu/h window shaker running most of day on low fan, temp on highest -- do not remember powered roof fan running -- have "smoke" tint film on storm windows, vinyl mini blinds, LOTS of shade. Storms protect regular wooden windows. used 1.74btu/DD/sf last month = mild =33 billing days 271DD 2133 liv sf.

    [Edited by cem-bsee on 06-24-2005 at 10:37 AM]

  3. #16
    Join Date
    May 2002
    Location
    Colorado
    Posts
    697
    Originally posted by docholiday
    I forgot to put blinds in the south windows ...Duh... they are bedrooms so I put min blinds at and the sensible drops to 19284 at 1000 cfm whcih knock the unit down to 2.5 ton.

    ....

    I
    I gather this home is in Houston.

    According to ACCA Manual S, a sensible load of 19,284 Btuh calls for 850 CFM (19,284/21/1.08). Engineering data for one particular 2.5-ton system shows 850 CFM will have 21,000 sensible and 7,000 latent capacities.

    If Doc's load estimate is correct, smp7015's system is large enough. The reasonable conclusion here is that the system was not installed or commissioned properly. I suspect improper refrigerant charge, high duct leakage, or low air flow. Add a TXV if the system does not have one.




  4. #17
    Join Date
    Jun 2005
    Posts
    37
    Thinks all. I appreciate it. I am going above the general contractor and I am going up the chain of command to get this fixed. I will keep everyone posted.

    All in all from what everyone is saying the ac is two small for the house. I guess when I get time I will measure actual square footage of the rooms.

    I will keep everyone posted.

  5. #18
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,428
    Originally posted by docholiday
    Ok, I get no where near that using J8.
    ... 21,115 Sensible.

    I am not sure what you used for windows, and no sense arguing it but I think he should do his own to be sure.
    Discussing Windows: CLEAR 270 S.F.
    Windows for each side as outlined previously.

    Doc,

    What did the analysis indicate for total BTUh due to Windows seperately?

    Did you use less than 270 S.F. in the Manual J analysis?

    BTUh/Sq. Ft. Window = _______

    Modelling of windows for clear or tinted may create almost an 100% difference.
    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. #19
    Join Date
    Jun 2005
    Location
    New York
    Posts
    207
    I know we are in the Business, In my house, when its 90 plus outside, I have no problem doing 70 deg inside(cooler if I want), I like to sleep w/ the blankets on, not naked and sweating, well maybe sometimes lol. If I have 20 plus people in the house, I still could do 70. Yes its different, we are in the business, I know that. I usually go alittle larger then the min needed, g-d forbid this family wants some company over or his wife wants to cook a meal on the stove, forget it! If I was doing that house, from here, I would have put a 3 1/2 ton in, no less then 3.

  7. #20
    Join Date
    Dec 2002
    Posts
    9,871

    As stated

    You are 1 ton short.

  8. #21
    Join Date
    Jun 2005
    Posts
    37
    Ok assuming he system is the right size by load anaylisis. It should still be able to get the house down to 75 degree's on a 95 degree day.

    What does the code say on what temp you have to plan a HVAC unit for. I can tell you that I took temps in every vent in the house. I am loosing 4 degree's from the return air duct to the return air plenum. Most of the vents that are away from the plenum are loosing any where from 6-7 degree's. It is coming out at 62-66 degree's at some vents. The air in the plenum after it leave's the evaporator coil is 59.9 degree's.

    At night when the attic is cool the ac seem's to cool ok. The problem is during the heat of the day when the attic reach's 130 degree's. Some of the smaller duct (I.E. utility room, bathroom by utility room) is coming out at 71 degree's.

    So either the unit is too small and not blowing enough air to make up for the heat loose in the duct or there is poor ventilation in the attic.

    This is a new track home and there shouldn't be a reason it can't get down to 75 degree's on a 95 degree day. That is why I believe the builder needs to fix the problem.

    I am turning in a warranty claim tommorro requesting that the problem be addressed and that they give me the copies of the load calculation's and building materials used in the house.

    From by research I believe it is building code that they have to do a load calculation on every house. Being that this is a track home I bet they didn't do one for each individual house. Taking this into account I believe this will be the best avenue for me to go. If they produce a load calc that I can get someone to verify the next approach I will take is to ask why the air is heating up so much in the duct when it leaves the plenum.

    Would everyone agree this would be the best approach to take?

    Thanks for everyone's effort's in this mess.

  9. #22
    Join Date
    Jun 2005
    Location
    New York
    Posts
    207
    In my opinion, just mine. Its going to be very hard to cool the attic down low enough to make that much of a difference. Yes, you could get it slightly cooler. Where do you live, I could give you a price on a 4 ton, just for the attic lol JUST KIDDING. I would, if I were you, and I dont know what legal ground you have to stand on, is to play hard ball now! Not have them come back and fix a small duct leak here and fix one there, reinsulate this and that and tint the windows or whatever, this will drag on forever. Get proof in writing or how ever you need to go about it and get the equipement replaced and upgraded to a 3 1/2 ton, even 3,The blower and evap(I dont know) maybe capable of doing 1200 cfm, the line sizes maybe sized okay and you would need a new out door machine ( I dont know yet and dont think so lol), I didnt go back 100 posts ago to see exactly what you have there now. Lets say you dont okay? Would you be happy to get 78-80 deg when its 95 out and thats without people in the house? NOT ME. I wouldnt subject any of my customers to that either. Anything other then equipement upgrade will be a bandaid IMO. I would be pissed.

  10. #23
    Join Date
    Jun 2005
    Posts
    37
    Update on square footage!!!

    Going of the appraisal for tax purpose's the total living area is 1840 square feet. This is calculated by the outside slab measurement and doesn't include the garage.

    When you do square footage for load calc's do you use the square footage figured from the perimeter of the house or actually measure all the rooms.

  11. #24
    Join Date
    Dec 2002
    Posts
    9,871

    definately

    Undersized. 4 ton would do the job.

  12. #25
    Join Date
    Apr 2004
    Posts
    7,680
    Well, I used the plan you gave me in your link and drew it using right draw, and its calculation came to 1577. If you add the garage which did not have dimentsions, I made it the same width as the MBR and overall right side of the house which was 19' wide and say 22' deep so if'n Im wrong you gave me bad info.

    For windows I used double pane (untinted) heat absorbing windows. I cant imagine he had a house built in Houston with single pane clear glass. I erased the file but I did use what I saw on the print from his link. I dont think it came to 270 sq feet of windows. I am not sure where that came from. Th HO will have to verify that information.

  13. #26
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,428

    Lightbulb It's the Windows

    Originally posted by smp7015
    Going of the appraisal for tax purpose's the total living area is 1840 square feet. This is calculated by the outside slab measurement.

    use the square footage figured from the perimeter of the house
    I used MID-Block ( or center of stud as the case may be) dimension to perform Manual J.

    A variation of 100 Sq. Ft floro area would only change the required tonnage by < 1/4-Ton and would likely not influence one's Equipment Selection.

    Ask an ARCHITECT ? ! Or Appraiser.

    ....=====================
    The SINGLE MOST IMPORTANT Factor in a Load Analysis
    are the WINDOWS.

    --------------...........
    Most Important Operating Factors.. Charge + Air Flow
    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

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