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  1. #1
    Howdy All,

    I live in one of the Atlanta suburbs. House is a two-story on full walk-out (daylight) basement. Cooling is done with two zoned AC units (not HP). Approximate heated-SqFt is 2,650 not including the basement, which is 1500/1150 down/up-stairs because of a two-story family and foyer rooms. I have no problems cooling the first floor.

    Just me and the wife. Master bedroom & bath are easy to cool. Three other bedrooms (one used as a home theater, one for a guest bedroom, and the last one as my office with two computers).

    I got up yesterday with zoned thermostat set to 74F. Went and did my yardwork and finished at just before Noon. Came indoors and turned on a computer to check email before taking a shower and set thermostat to 73F. Some 45-minutes later I go into the master bedroom to set thermostat to 72F (I'm a Yankee) before stepping into shower, and noticed temp was now reading 73F. All seemed normal.

    Got out of the warm (but not hot) shower and temp was not 74F. Okay. Go run some errands and notice two hours pass and thermostat still at 72F setting, but temp reading still at 74F. I turn off the PC I had left on and went about watching some TV downstairs. I noticed its thermostat was set to 74F and the current temp was also 74F. Outside it was 84-86F. Yesterday's high about 89F.

    Coming up on 4PM I noticed the upstairs unit is still running non-stp and the reading/setting is still unchanged at 74/72. Downstairs its cycling per a normal, expected behavior. Its idea of 74F is much cooler than upstairs. Both floors have 9' ceilings and their respective thermostats mounted at about 5'6" height from the floor.

    I relax downstairs, do some grilling, snoring, drinking, etc. until 8PM rolls around when its X-Box Live time. My every-Saturday night keeps me downstairs with the guys online playing shoot'em up games. I went to bed at 1AM.

    I walts upstairs at 1AM and the thermostat is set where I put it and its still reading 74F. I have an alcohol thermometer hanging on the wall in my study and its reading 29C, or about 84F at 1AM. So, in 11 hours between 2PM yesterday and 1AM today nothing was running upstairs except the fire-alarms and the thermostat itself.

    I have two concerns: 74 reading downstairs and upstairs have obvious differences (ones much cooler in reality). When a track-home is outfitted for HVAC what temp do they size the units for? This isn't a heat pump, but a dedicated AC+Furnace setup, and zoned for floors.

    I'm not so sure the tubular conduits in the attic, where the second floor zone is located, is keeping the chilled air cool enough by the time it hits the ceiling registers. My attic, which is a moonscape of uneveness covered in blown fiberglass, is very unfriendly--making going up there not desirable.

    So, far the HVAC has run non-stop for 3-4 hours and not reached the point of where I set it to. Its warmer upstairs right now with reading/set temps of 72/71 than downstairs at 74/75. I am not sure if the demands an attic fan or not, and also where to install it.

    I think a ridge/peak located fan could help remove some of the 120F temps in the attic in favor of the 88F temps outside. I think its the heated shingles generating the heat in the attic, and then placing a load onto the upstairs area. I'd install the fan myself, but that peak goes up 18 feet.

    Any ideas for testing, evaluating, etc. the situation more formally? I'm ready to call an HVAC person, but the idea of spending $3K to upgrade is not a laughing matter.

  2. #2
    Join Date
    Jun 2005
    Cooling design temp is usally 78. So if you want to run it colder it may have problem doing that.

  3. #3
    Well, that would certainly explain it. I did not know this, and I bet most homeowners & homebuyers probably don't know this either. Is this something that is typical for all regions in the USA or just the South?

    I guess its another nail in the cookie-cutter home coffin. Had I known this bit of information, I'd not have bought the house. Period. Essentially, I now learn I bought a joke as its going to cost me big (well, for me) to keep me comfortable.

    I think I will do my part and spread this news, especially to first-time ignorant buyers (like me). I get a whopping 10 delta on $3K/zone systems. Jeez.

  4. #4
    Join Date
    May 2004
    You will find that here in Atlanta that your refrigeration equipment is sent to us using a 90* ambient outdoor temp. When you reach that 90* temp the capacity of the system drops.

    I dont know when all of this happened but the increase RH has been off the scales for weeks now. This will test your systems limits just that much more. It is not just how hot but how hot it feels. Today was a 102* feel like day.

    Yes, then again, you have a cookie cutter house but your delta should be much more than 10*. Have a system check up with superheat and subcooling calculations taken as soon as you can.

    We are in for a few more weeks of this heat/humidity so hang on to your hat.


    your system will kick serious butt if it pulls down 20* below the outside ambient... 90 outside = 70 inside at best....

    [Edited by lusker on 07-24-2005 at 11:44 PM]

  5. #5
    I just checked the 30680 (home) and 30324 (work) temps: 90F/52% RH for HI of 96F, and 93F/50% RH for HI of 101F.

    Somehow, the idea of an average relative high in Summer being 78F seems meaningless.

    BTW, as a silly experiment, I got up today at 7:20AM and set the upstairs AC to 70F. Its actually reached and held that temp for some time, but in the last hour the reading at the thermostat was 72F and climbing. To constrast this, downstairs is and has been set to 74F all day and its actually a lot cooler downstairs than upstairs.

    In my bedroom-converted-to-computer-room, the alcohol thermometer is reading 25C, or about 77F. And the wife would like me to set the upstairs thermastat to something like 74-75F before I leave for work at 2:30PM today (she's already at work).

    I'm sleeping downstairs on the couch tonight, where it is comfortable for this Yankee.

  6. #6
    Join Date
    Jun 2002
    As a fellow homeowner in the same area, I'd say it would be worth having it checked out.

    You didn't say what size your systems were, but I'm cooling 1100 square feet upstairs with a 2-ton non-zoned system that is also completely enclosed in the attic (ductwork and airhandler), and it can hold 74F fine (well, at least so far but today will be an interesting test with temps in the mid 90's). I may be eating crow when I get home today.

    Granted, it has no pull-down capacity at all in the late afternoon and runs constantly beginning at 4-5PM everyday until 7-8PM or so, but it works.

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