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  1. #1
    Join Date
    Jun 2005
    Posts
    1

    Angry

    We moved into a new home in October in Virginia. The house has 4200 square feet of finished living space on 3 floors. Typical temps are 90-95 July through Sept., and it has been 88-90 the last few days.

    The top floor is about 700 of the 4200. We asked the builder if the units would be sufficient to cool 3 floors. The answer was, "we have been using the same HVAC on this floor plan with 3 levels and have never had any issues."


    Now that it is June, our 2nd floor will not go below 75, no matter how low it is set, and the 3rd floor has been 82 even though it is set on 68. There are 5 other homes on our street with similar issues. These inside temps are at 8:00pm!!!! This is not satisfactory to me after spending 500k on a house to have this occur. Any idea how I can prove that the units are not sufficient? The builder had the HVAC company come out and do more freon, as well as adjust the dampers. It is even hotter now!

    What they installed was the following.
    Lennox Merit Series
    10ACC-030-230 2.5 Tons (First floor)
    10ACC-036-230 3 Tons (Second and Third)

    That is only 5.5 tons of cooling for 4200 sft? I had read online that 1 ton per 500sft was a good estimate (That would mean a minimum of 8 tons)?

    Any advice on how I can prove that this is BS would be appreciated! Any reources that will prove this so I have some leverage to get them to change this?


    Scott

  2. #2
    Join Date
    Jun 2004
    Location
    Florida
    Posts
    556
    Forget that 500sqft per ton rule that is way off for residential construction.

    Sometimes the problem with a unit isn't discovered the first time someone looks at it. You should probably call the HVAC contractor and tell them that it still isn't working. If you don't trust them you should pay to have another company out for a second opinion.

  3. #3
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Dhanna ,gave you good advice.

    I'd try to deal directly with the installing contractor,instead of the builder,if they are any good they will get it resolved.

    The system size could easily be correct.It may have only been designed to maintain 75 or 78F,but you'll have to ask ,it should not be 82.

    Could be a duct problem.

    If you have to get another contractor,try Cropp-Metcalf ,if they are in that part of the state.

    [Edited by dash on 06-09-2005 at 10:47 AM]

  4. #4
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,347
    The builder had the HVAC company come out and do more freon, as well as adjust the dampers. It is even hotter now!
    A proper heat load calculation notwithstanding, it sounds to me you may be facing more of an installation issue than sizing concern. If the HVAC company added more refrigerant and your cooling performance got worse, it's possible the unit was overcharged or full of non-condensibles initially and gassing it only aggravated the matter.

    Of course, there's a million other things that could be affecting performance, such as ductwork design and integrity, proper piston size installed if system uses piston vs. TXV, blower speed, etc.

    I wouldn't look at sizing until all installation issues have been ruled out.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  5. #5
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,586
    You did not mention the first floor. You must also cool this floor since the upper floor units will not be able to cool you entire home. Also usally units are sized for window shading, try that!
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  6. #6
    Join Date
    Mar 2005
    Posts
    21
    I had to deal with a similar issue with new construction. The interesting issue was the electricial and plummer that were sub contracted were first rate. The ac guy was third rate. After getting some advise on this site about next steps, I accepted the fact that it had to be fixed and went with someone the plummer recommended and after talking to him and getting references am goin with him.

    as a bonus I decided to upgrade to a variable speed unit. Planned install is later this month.

  7. #7
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,295

    Lightbulb Complexity of Resolution

    Originally posted by smit5454
    Now that it is June, our 2nd floor will not go below 75, no matter how low it is set, and the 3rd floor has been 82 even though it is set on 68.

    There are 5 other homes on our street with similar issues.
    These inside temps are at 8:00pm!!!!

    This is not satisfactory to me after spending 500k on a house to have this occur.

    Any idea how I can prove that the units are not sufficient?

    Lennox Merit Series
    10ACC-030-230 2.5 Tons (First floor)
    10ACC-036-230 3 Tons (Second and Third)

    That is only 5.5 tons of cooling for 4200 sft?

    I had read online that 1 ton per 500sft was a good estimate (That would mean a minimum of 8 tons)?

    Any reources that will prove this so I have some leverage to get them to change this?
    Ask builder for a copy of the Manual J calculation that the A/C contractor performed?

    SEE comment by SHOPHOUND ... First Step.

    Secondly,

    1 ton per 500 Sq. Ft ... gets one " in the ball park"
    ... That's what rules-of-thumb are for ... ' guessing ' .. Not a Final equipment selection.

    Window size / tinting/ shading / orientation must be
    reviewed to determine equipment selection for each floor.

    Typical 4,200 house may have about 800 Sq. feet of glass in the windows and sliding glass doors.

    GENERALLY SPEAKING :
    CLEAR glass ( NO tinting ) will require about 42,000 BTUh
    or > 4-ton unit. 4ton unit has ~ 48,000 BTUh total capacity and ~ 36,000 Sensible Load Capacity.

    S.H.G.C. of < 0.45 ( i..e ANDERSON monolithic grey)
    will reduce that load to ~ 26,000 BTUh.

    Note: ~ 1.5 ton difference due to Tinting differences + actually window size + orientation.

    First Floor area ______ ~ 1700 Sq. Ft.
    Windows
    .Direction
    .... Total Window and Sliding Glass Door Area

    N ______ Sq. Ft./..SHGC _____ U-value ______
    S ______ .......//...... _____ ...... ______
    E ______ .......//...... _____ ....... ______
    W ______ .......//...... _____ ....... ______

    S.H.G.C. Solar Heat Gain Coefficient

    Same for 2nd & 3rd ____ ? 2,500 Sq. Ft.

    N ______ Sq. Ft./..SHGC _____ U-value ______
    S ______ .......//...... _____ ...... ______
    E ______ .......//...... _____ ....... ______
    W ______ .......//...... _____ ....... ______

    Any overhangs ( i.e. porch) > 4 feet?
    Let me know SPECIFICS & I'll do a "Quick Load" estimate.

    IF ALL 5 houses, can not provide < 76'F then there Could Be a equipment sizing issue.

    However, if 3rd floor can not be cooled sufficiently
    at 8 PM with
    the A/C units AND air distribution set-up properly
    then it seems like the insulation or other Building Envelope issues may be the REAL Root Causes.

    What are the Inside Temperatures for each house
    at 9PM? 10 PM?

    Scott,
    Seems to me that You
    ALREADY proved that the units are NOT sufficient
    IF ALL 5 have Similar problems.

    The complexity of a problem resolution is in trying to ascertain whether it's an operation / building envelope issue or equipment sizing concern that is The Root Cause.

    [Edited by dan sw fl on 06-09-2005 at 02:12 AM]
    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

  8. #8
    Join Date
    May 2002
    Location
    Colorado
    Posts
    697
    What gets me is that builders sell houses for $500,000 or more with builder-grade air conditioners that have no TXVs, no safety switches, no restart delays, but lots of decibles. And they are installed by the low bidders, who usually don't know what they are doing. Sad.

    The house probably has a $7,000 SubZero refrigerator!

  9. #9
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Or a top of the line whirlpool tub,that cost more then the HVAC.



    smit5454,No offense,but the builders pressure for low cost ,on things buyers don't pay a lot of attention to,like HVAC,is likely part of your problem.

    Hope the HVAC people can get it squared away for you.

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