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  1. #1
    Join Date
    Jun 2005
    Posts
    1
    I have been reading several posts over the last few days and I hope I am giving enough info here for someone to help me out.

    I have a new house and the a/c will not cool the house down past 80 during the heat of the day. In fact the temp will climb to 80 from 75 in the morning. The unit will run from 7am until 9pm non-stop

    The house is located in NE Ohio and the rear of the house faces South West and gets sun all day long. The house is a 3200 square foot colonial with a walk out basement and has 13 very large windows in the back, 8 of which are in a sunroom that has exposure to the East South and West. I do not have any blinds on the back of the house yet. I will be installing those very soon. I have all of the vents in the basement turned off to help get the air to the main floors.

    The outside temps have been in the upper 80s and low 90s during the day and going down to upper 60s low 70s at night.

    The unit is a Trane XB10, 4 tons and is located on the West side of the house. There are no trees as of yet, housing development was an old farm.

    I have checked the temps at the register, closest to the unit is 64 and upstairs is 67.5. My main concern is this unit is simply too small for the house. I do not know what type of calculations were performed to arrive at the unit size, I have a call into the builder to have the HVAC people come out.

    I am looking for any information on this, is the unit too small, what should I ask the HVAC contracter to do. Is this acceptable? I have ready 1 ton per 400 sqft, that would be an 8 ton unit, which seems a bit much. Basically I am looking for any help I can get so I can have this resolved.

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,243
    Forget that XXX BTU per sq ft crap. Only a GOOD load calc will tell. Most load calcs "ASS-U-ME" that shades, blinds, something will be used and closed in a hot spell. I'd get the east, south & west windows covered then see how it does.

  3. #3
    Join Date
    May 2002
    Location
    Colorado
    Posts
    697
    Ask him (nicely) to fix it so it cools your house. You might also ask him to write down for you all his measurements (pressures and temperatures) and calculations (superheat and subcooling) for you. If it still does not cool your house, post all those figures here and ask what the problem might be. I suspect it is not properly charged or has a problem caused by poor installation.

    You might also ask him if it has a TXV (aka TEV). If it doesn't, ask him how much $ to install one. If A system with a TXV is much easier to charge correctly and is more forgiving of small charging errors.








  4. #4
    I have checked the temps at the register, closest to the unit is 64 and upstairs is 67.5.
    -----------------------------
    These temps seem pretty high, even if it's 80 degrees in the house. The rule of thumb says you should get an 18 - 20 degree temp drop across the evaporator coil. If it's really humid you might be able to get away with 16 to 18 degrees, but that's pushing it, IMHO.


  5. #5
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635
    Rules of thumb ARE a load of bull puckey. But you're current 800 square feet per ton is very high compared to most. I know a builder whose current experiment is at 1000 square feet per ton. But he's building his houses like Thermos bottles. The insulation contractor charges three times what most do to build those houses like that. I doubt your house is so well insulated. With all those windows and all that square footage I'm betting that your Manual J comes in a fair amount higher than 4 tons.
    Originally posted by hvac student_4063
    ...you might be able to get away with 16 to 18 degrees, but that's pushing it, IMHO.
    Mostly true... unless you're pushing 500 CFM per ton. In that case 18 degrees gives you an awesome .81 sensible. Well, it's awesome for this dry area.

  6. #6
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,296

    Lightbulb Hit the Nail on the Head

    Originally posted by robh
    The house is located in NE Ohio and the

    rear of the house faces South West
    and gets sun ALL Day long.

    The house is a 3200 square foot colonial with a walk out basement

    and has
    13 very large windows in the back,
    8 of which are in a sunroom that
    has exposure to the East South and West.

    I do not have any blinds on the back of the house yet.
    I will be installing those very soon.

    I have all of the vents in the basement turned off to help get the air to the main floors.

    ... outside temps ... upper 80s and low 90s during the day ... down to upper 60s low 70s at night.

    The unit is a Trane XB10, 4 tons

    I have checked the temps at the register, closest to the unit is 64 and upstairs is 67.5. My main concern is this unit is simply too small for the house. I do not know what type of calculations were performed to arrive at the unit size, I have a call into the builder to have the HVAC people come out.

    I am looking for any information on this, is the unit too small, what should I ask the HVAC contracter to do. Is this acceptable? I have read 1 ton per 400 sqft, that would be an 8 ton unit, which seems a bit much.
    Rule-of-thumb:
    1 tons for 350 to 900 sq feet per ton
    works for EACH, specific architectural design.

    Close to NO windows ( <12% glass to floor area ratio .. VERY VERY RARE ) and you'll end up with ~ 900 Sq. feet per ton.

    Lot of windows ( 30% of floor area, i.e. 1,000 square feet in 3,300 square foot home ) and one would be VERY CLOSE TO 400 Sq feet per ton.

    All based on My EXPERIENCE running Manual J EVERYDAY on FL " lots of windows" architecture. Yes, I have had some residence come in at 350 Sq. feet per ton. The highest was ~ 750 sq. feet per ton due to SMALL total glass area ( " non Florida like ") and THE LOWEST I have encountered in my caseload history of maybe 300 SOME large, Custom, Unique homes.

    i.e. 7,200 Sq foot with 800 square feet of well TINTED glass = ~ 10 tons, designed last fall and numbers are just a little fuzzy .. BUT ...

    ........ Are YOU GETTING THE PICTURE ...

    ....... IT'S ... ALL .. ABOUT WINDOWS.
    ....... TOTAL AREA .+. TINTING .+. ORIENTATION

    ( assuming one is 'better than code' in other building envelope features ..
    NO infilration or insulation "ISSUES")

    OPERATION IS
    LIKELY _NOT_ THE
    MOST SIGNIFICANT PROBLEM
    IF slightly More than 16'F DELTA T is maintained.

    3,200 sq. feet with 600 + square feet
    (<20% glass to floor area ratio) of total glass area
    may be in the 500 TO 650 Sq Feet per Ton range.

    ******************************_____********
    YOUR RESIDENCE REQUIRE$ SIX 6 +/- Tons! !!
    ******************************_____********

    YES, THIS 3,200 Sq. FOOT RESIDENCE
    WITH _REAR FACING SOUTH WEST_
    WITH _LOTS OF WINDOWS_
    HAS A _VERY HIGH PROBABILITY_
    OF BEING A BLATANTLY, MIS-GUIDED A/C DESIGN.

    Partial Solution:
    Sunroom SHALL NOT be air conditioned ! !! !!!
    ( assuming it is now ... )
    8 "Very Large" (i.e. 4' x 6') windows seems to be 180++ square feet ... that't about 1.5+ TONS right there given a set of unfavorable conditions ..little tinting and nearly worst case orientation (= rear of house faces South West)

    Very Short term solution: ISOLATE the SunRoom.

    Other ideas ... I would require plans, review house orientation and have window specs ( S.H.G.C.) + interior window treatments IN-Hand in order to develop an applicable Manual J.

    FURTHER guidance may be available.
    Dan .. 800 COLD AIR

    I Can Only Hope this GENERAL Guidance
    gets you headed towards
    a Reasonably Comfortable environment.

    [Edited by dan sw fl on 06-10-2005 at 06:36 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

  7. #7
    Join Date
    Jun 2005
    Posts
    1

    Frown Trane Not Cooling Either

    We just invested in a Trane because we thought it would be the best quality based on a high price of 8000 vs the 3000 janitrol it is replacing. Wrong so far!!!! The installation company seems very reputable and has guaranteed our satisfaction but the 2 tone unit 4twx4024a did not cool our 1000 sq ft upstairs nearly as well as the 2 ton janitrol. they just replaced it today with a 2.5 4twx4030b(not "a") which is supposed to be 2.5 ton. they assured me this would do the job but it's been 2 hours set a 69, 84 outside and still 73 in here. It's a little better but i am still waiting and still disapointed.
    Let me know how yours works out.
    peteandtess@charter.net

  8. #8
    Join Date
    May 2002
    Location
    Colorado
    Posts
    697

    Re: Trane Not Cooling Either

    Originally posted by ptintle
    We just invested in a Trane because we thought it would be the best quality based on a high price of 8000 vs the 3000 janitrol it is replacing. Wrong so far!!!! The installation company seems very reputable and has guaranteed our satisfaction but the 2 tone unit 4twx4024a did not cool our 1000 sq ft upstairs nearly as well as the 2 ton janitrol. they just replaced it today with a 2.5 4twx4030b(not "a") which is supposed to be 2.5 ton. they assured me this would do the job but it's been 2 hours set a 69, 84 outside and still 73 in here. It's a little better but i am still waiting and still disapointed.
    Let me know how yours works out.
    peteandtess@charter.net
    Did they perform a Manual J calculation before they decided on the size?

    Has it been really humid lately? An air condtitioner has to remove excess humidity before it can cool down the air.

    Did they install a TXV? If not, get them to.

    If the old system worked better than the new one with the same tonnage, don't you suppose there is something wrong with the way they installed or commissioned the new one?


  9. #9

    My 2 Ton Trane provides 50 degree cool air

    Sounds like something is wrong with your A/C system (leaked refrigerant, leaky ducts, dirty filter?) if your register air is not colder than 67 degrees. Even with cool 50 degree air coming out of my registers, my Trane A/C does not provide rapid cooling but is gradual which I prefer in order to dehumidify properly. We are happy to keep it at a steady 74 degrees with around 40% humidity, but to achieve that in our 1300 sq ft house with a S/W exposure, the system runs for long stretches on hot sunny days.

    My Trane XL13 was installed in the winter 2 1/2 years ago and when I got around to using it 2 years ago, all of the refrigerant had leaked out but the installer provided an excellent service guy to fix my system which is still working great in its third season.

  10. #10
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,296

    Re: Trane Not Cooling Either

    Originally posted by ptintle
    they assured me this would do the job but it's been 2 hours set a 69, 84 outside and still 73 in here. It's a little better but i am still waiting and still disapointed.
    You have WAITed a WHOLE 120 Minutes. WOW ! !!

    69'F ... Are you storing Meat?

    On the more note-worthy side,
    Cooling on a GOOD A/c system might only
    be ~1 or 2 degrees per hour
    depending on the time of day.

    What's the deltaT?
    %R.H.?

    %R.H. may be HIGH given ~70'F.
    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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