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Thread: Sizing AC Unit

  1. #1
    Join Date
    May 2001
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    41

    Sizing AC Unit - Whole House or Zone???

    We have just had our heating/cooling system zoned into 4 zones using a Honeywell Trol-A-Temp system. We are considering replacing the AC unit which is a 3.5 ton unit with a smaller one. I used the HVAC Calc Residnetial software(Great Program - Very Intuitive and Easy to Use) and came up with a total heat gain for the building as 33,789. The largest heat gain in any of the zones is 16,300. How do we size the AC unit? Since there is a foyer, there will be heat flow between the zone.

    Thank you for the help.



    [Edited by fmwaz on 05-17-2001 at 11:25 AM]

  2. #2
    Join Date
    Jul 2000
    Location
    Ottawa, Ont. Canada
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    1,729

    more information

    Hi, I believe there is one more piece of information I would like to add here. I spoke to fmwaz on the phone and he told me that the way the duct zoning works with this system is only one zone gets air at a time and the dampers are down at the furnace essentially blocking off 2 zones as one gets fed. I am not up on the Trol-A-Temp system but if this is correct, I would be concerned about putting in a 3 ton because there wouldn't be enough air flow over the coil. Can somebody with experience with the Trol-A-Temp system please reply and give me an education on how it works?

    Thanks

    don
    don sleeth - HVAC-Talk Founder
    HVAC Computer Systems
    Heat Load Calculation Software

  3. #3
    Join Date
    Nov 2000
    Location
    Ottawa, On. Canada
    Posts
    32

    Smile Trol-A-Temp

    Originally posted by Don Sleeth
    Hi, I believe there is one more piece of information I would like to add here. I spoke to fmwaz on the phone and he told me that the way the duct zoning works with this system is only one zone gets air at a time and the dampers are down at the furnace essentially blocking off 2 zones as one gets fed. I am not up on the Trol-A-Temp system but if this is correct, I would be concerned about putting in a 3 ton because there wouldn't be enough air flow over the coil. Can somebody with experience with the Trol-A-Temp system please reply and give me an education on how it works?

    Thanks

    don
    I'v never worked on the trol-a-temp system but try this website http://hbctechlit.honeywell.com/.
    Dave

  4. #4
    Join Date
    May 2000
    Location
    Atlanta,GA.USA
    Posts
    210

    zone

    zoning is basicly, a themostat controls each zone.
    1 2 3
    I'm concered when people want to change there units.
    what if you want all zone's on the 3.5 cooled it all
    if you drop to a 3 ??
    i do get much work for this but have some ask an will
    be getting into it more.

  5. #5
    Join Date
    Apr 2001
    Location
    Arkansas
    Posts
    2,111

    Hmm

    If his zone system shuts down all zones but one at a time, he's got problem with it. Just as Dependsaservice said the unit is controlled by a master thermostat and the other stats control dampers.
    "FIGHT CRIME: SHOOT BACK"

  6. #6
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,900
    Each stat can bring on the equipment and open the damper for that zone. It is possible for a 3.5 ton unit to be feeding a duct designed for a fraction of that. Therefore, if properly installed, a bypass damper is used to return the excess back to the A/C. With Trol-a-temp's newest panels, they have a thermistor that goes in the supply and monitors for overheat or near freezing conditions to shut off the equipment before a coil freezes or a furnace cycles on limit. If the system does not have a bypass or the Zonemax sensor isn't used, he will have problems.

    As for his gain, seems to me he has a 3 ton heat gain and when the A/C is changed, it should be to a 3 ton.

  7. #7
    Join Date
    Jul 2000
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    Ottawa, Ont. Canada
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    ah, that makes sense

    Thanks Baldloonie, the bypass damper was the piece of the puzzle I was missing. With that in place, then yes a 3 ton is what's called for or even save the expense and go with the existing 3.5 if it is a good working unit. His contractor was suggesting a smaller unit, I think because of the air flow, so I hope he was aware of the bypass damper. If he wasn't, I am sure he will be shortly

    don

  8. #8
    Join Date
    Jun 2001
    Posts
    3,910
    Originally posted by r22d22
    Read
    Read What ?

  9. #9
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,024
    Originally posted by bb
    Originally posted by r22d22
    Read
    Read What ?
    Still lost yet again, but I can relate to your bio. in your profile.

  10. #10
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,024
    Hey, I like ideas, I even get a couple now and then. What's yours.

  11. #11
    Join Date
    May 2001
    Location
    Kansas City
    Posts
    2,729
    Originally posted by r22d22
    Originally posted by bb
    Originally posted by r22d22
    Read
    Read What ?

    bb and lynn rodemayer don't know what to read.
    (nothing)
    A windows macro cause me to submit some strange entries without knowing it. But the replies were deliberate.
    This gives me a great ideal.
    Windows macro? Or drugs?

  12. #12
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,024
    Hey Mr. Smith. Which company do you work for? If you don't want to say, just reply bug off.

  13. #13
    "bb and lynn rodemayer don't know what to read.
    (nothing)"

    This is logically incorrect. What your are saying here is BB and Lynn know what to read. (everything)

    Jeff

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