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Thread: Sizing question

  1. #1
    Join Date
    Jul 2004
    Location
    Indiana
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    27
    2200 SQ FT 10FT CEILINGS BROTHER IN LAWS 3 TON CONDENSER CAN ONLY GET TEMP TO 77 WHEN T-STAT CALLS FOR 69 AND COMPRESSOR THERMAL O/LSs After 45 minutes or so kicks on (Compressor).
    Again this is only when ambient is 90+. Would a larger condenser and A coil HELP THIS Delima..? wHEN IT COOLING REGISTER AIR IS 64 DEG

    CAP. TUBE

    AMBIENT 89
    LIQUID L PSI 228
    TEMP LIQ LINE 90

    iNDOOR WB 64

    SUCTION PSI 70
    SUCTION LINE TEMP 75 AND SWEATING
    CALCULATED 10 DEGRES SUPERHEAT + OR -5 DEGREES

    GOD BLESS ARE VETERANS Living and Deceased so we can practice our PROFESSION HAVE A PROFITABLE DAY

  2. #2
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    Mar 2005
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    Suppy NC
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    4,509
    do manul j and see what it calls for

  3. #3
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    Nov 2004
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    SW FL
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    Undersized & Underperforming Combo?

    Originally posted by fatcat
    2200 SQ FT
    10 FT CEILINGS
    3 TON CONDENSER, 77'
    When it is COOLING REGISTER AIR is 64'
    BOTH Undersized and Underperforming:
    ___Underperforming based on 13'F Delta T air flow.

    ___Seems significantly __Undersized (needs At Least 4-ton or maybe even a 5-ton) based on my experience performing ACCA Manual J 8th edition analysis on 300+ custom homes.

    However, you have not provided:
    1. R-values for Walls
    2. R-value of Ceiling
    3. Window Area
    (including Sliding glass doors) on EACH Side of house
    4. Windows CLEAR or Tinted
    5. House Orientation

    MORE Later in Update or Follow-up

    [Edited by dan sw fl on 06-26-2005 at 12:54 PM]
    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. #4
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,389
    First thing to do is find out why comp won't stay running. Undersized unit working properly can run 24/7 without failing. You say register air only 64. Also take readings of supply & return right at the unit and see if you are picking up considerable duct heat gain.

  5. #5
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,543
    I think you had better find out why it is overloading and i think the house will cool better!
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  6. #6
    Join Date
    Nov 2004
    Location
    SW FL
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    Calc by Aprpox. Manual J Method

    Summary of Approx. Loads

    .......WINDOWS.. 15,444 BTUh CLEAR GLASS 280 S.F.
    .......CEILING.. 6,368 R-19
    .........Walls.. 2,292 R-19
    .........Floor....... 0
    .........DUCT.....6,286 R-6 in 130'F Attic
    .INFILTRATION.....2,420
    .INTERNAL Gains...2,977
    .........People...1,466
    _________TOTAL___37,153. BTUh = 4-Ton
    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

  7. #7
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    Jul 2004
    Location
    midwest
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    2,868
    Dan, I know everything your doing is trying to help but why give these loads without knowing the needed info. There is most likely a contractor that is trying to fix this and you giving incorrect information will only make matters worse. His first problem is getting the unit working like it should and then he can see if there is a size problem.

  8. #8
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    Jan 2004
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    Lancaster PA
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    66,763
    I hope that suction line temp of 75 was a type o, error.

    70 psi is a saturation temp of 41, that would give you 34 superheat.
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    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    Originally posted by beenthere
    I hope that suction line temp of 75 was a type o, error.

    70 psi is a saturation temp of 41, that would give you 34 superheat.

    Which would explain the compressor going out on over load.
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    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  10. #10
    Join Date
    Feb 2003
    Posts
    538
    Assuming your readings are right it appears overcharge w/ a restriction

  11. #11
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    SW FL
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    Lightbulb Parallel Path Processing

    Originally posted by trane
    His first problem is getting the unit working like it should and then he can see if there is a size problem.
    Following PARALLEL SIZING & Performance Paths
    is a COMPLETELY ROUTINE Evaluation Process
    which requires a couple iterations.

    DEVELOP THE WHOLE PICTURE.

    If you can't stand the heat, get out of the kitchen.

    Fatcat,

    It is QUITE OBVIOUS within < 7-minute evaluation that
    75'F will never be consistently achieved at Outside Design Temperature with a Good performing 3-ton unit, UNLESS there are < 130 S.F. TOTAL AREA of Tinted windows in this 2,200 S.F. house.

    NEARLY ALL (i.e. 97%) U.S. HOUSES
    HAVE > 10% RATIO OF GLASS-TO-FLOOR AREA.

    I'd say __< 1% chance__ of this 3-ton being the most appropriately sized unit in this case.
    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

  12. #12
    Join Date
    Jul 2004
    Location
    midwest
    Posts
    2,868

    Re: Parallel Path Processing

    Originally posted by dan sw fl
    Originally posted by trane
    His first problem is getting the unit working like it should and then he can see if there is a size problem.
    Following PARALLEL SIZING & Performance Paths
    is a COMPLETELY ROUTINE Evaluation Process
    which requires a couple iterations.

    DEVELOP THE WHOLE PICTURE.

    If you can't stand the heat, get out of the kitchen.

    Fatcat,

    It is QUITE OBVIOUS within < 7-minute evaluation that
    75'F will never be consistently achieved at Outside Design Temperature with a Good performing 3-ton unit, UNLESS there are < 130 S.F. TOTAL AREA of Tinted windows in this 2,200 S.F. house.

    NEARLY ALL (i.e. 97%) U.S. HOUSES
    HAVE > 10% RATIO OF GLASS-TO-FLOOR AREA.

    I'd say __< 1% chance__ of this 3-ton being the most appropriately sized unit in this case.
    Or the 2200 sq. ft. includes a basement, earth contact home, foam and concrete walls, foam insulation, the list goes on. If it was a home that I had sized I wouldn't want someone guessing on the internet and telling the homeowner I had installed the wrong size. I hope you see my point.

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