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  1. #1
    Join Date
    Mar 2008
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    Confused Questions about Two-Stage AC

    1) Is there any good, hard data on comparing the efficiency of a two-stage 15 SEER vs. a standard single-stage 15 SEER units? I recognize that heat load will determine how often the 2nd stage is used but I would expect at least some data such as "Assuming 80%/20% 1st/2nd stage operation the SEER is xx). I'm surprised too see the cost savings I got from my dealer didn't include this. This looked like it came from Bryant and was based on the second stage always being used.

    2) Are there reliability issues with these units compared to single-stage? The exact unit I'm considering is the Bryant 187ANA (2-stage reciprocating) vs. the 165ANA (single-stage scroll). From what I read here the 2-stage reciprocating units sounds like it will have a smaller first stage output than the two-stage scroll unit (180A).

  2. #2
    Join Date
    Sep 2002
    Location
    I don't know
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    2,903
    You would have to look at performance datasheets to get that info.

    What's really important is how a unit operates on hot weather; it's possible to have a high efficiency two stage unit which performs no better than a low end 13 SEER model in peak conditions.

    SEER is an average figure which takes performance under varies sets of operating conditions into consideration; what you need to pay attention to is EER.

  3. #3
    Join Date
    Mar 2005
    Location
    burlington county n.j.
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    9,703
    2 stage will make it more comfortable not more efficient. 15 seer is 15 seer.

  4. #4
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,568
    I do believe they can show how much would be saved by reducing the number of cycles per day. But the testing used does not consider this for comparison sake.They only test at full load, but you can be sure it will save some $$$ per month. I bet you reduce compressor cycling 20-50% and that has to save a good percentage.
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  5. #5
    Join Date
    Mar 2008
    Posts
    16
    Quote Originally Posted by t527ed View Post
    2 stage will make it more comfortable not more efficient. 15 seer is 15 seer.
    OK, let's assume a 4-Ton 2-stage is 15 SEER. Is that still true when only the 1st stage is operating? If it is then I effectively have a 2-Ton 15 SEER AC one those days when I don't need a full 4-Ton cooling system, right?

    Maybe a simple example will hep illustrate my point:
    Assume the cooling period in Maryland runs from May though Sept. and that only August is hot enough to require the 2nd stage Then, under these simplified conditions, wouldn't a two-stage AC be more efficient, overall not SEER, than a single-stage?

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,712
    I don't have first and second stage SEER specs for Carriers.
    I have them for York.
    In first stage, the SEER is .25 to .75 more then in second stage.
    So, you might save an extra 3 to 10 dollars over a single stage as far as efficiency.

    You may save more, if it is able to get your RH down to 45%, most people find they can set their stat acouple degrees higher in that case.
    As the others have said, 2 stage is for comfort, not savings.

    The 2 stage units have been out for quiet some time now, and are proving reliable.
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  7. #7
    Join Date
    Mar 2008
    Location
    Houston, Texas
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    352
    Quote Originally Posted by t527ed View Post
    2 stage will make it more comfortable not more efficient. 15 seer is 15 seer.

    Seer rating doesn't even apply to my area, when u grow up I'll tell you about it.

    The system is there for comfort.............they just don't know

  8. #8
    Join Date
    Mar 2005
    Location
    burlington county n.j.
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    9,703
    Quote Originally Posted by Roboman View Post
    OK, let's assume a 4-Ton 2-stage is 15 SEER. Is that still true when only the 1st stage is operating? If it is then I effectively have a 2-Ton 15 SEER AC one those days when I don't need a full 4-Ton cooling system, right?

    Maybe a simple example will hep illustrate my point:
    Assume the cooling period in Maryland runs from May though Sept. and that only August is hot enough to require the 2nd stage Then, under these simplified conditions, wouldn't a two-stage AC be more efficient, overall not SEER, than a single-stage?

    seer will be higher on low stage but unit will run longer...

  9. #9
    Join Date
    Mar 2005
    Location
    burlington county n.j.
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    9,703
    Quote Originally Posted by Skip 2 my lou View Post
    Seer rating doesn't even apply to my area, when u grow up I'll tell you about it.

    The system is there for comfort.............they just don't know


    hey i'm all growed up, let er rip........

  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,712
    Quote Originally Posted by amd View Post
    You would have to look at performance datasheets to get that info.

    What's really important is how a unit operates on hot weather; it's possible to have a high efficiency two stage unit which performs no better than a low end 13 SEER model in peak conditions.

    SEER is an average figure which takes performance under varies sets of operating conditions into consideration; what you need to pay attention to is EER.
    You know the estimated anual cost that the ARI post, is based on SEER, not EER.
    The rating people don't use EER to estimate operating cost.
    So unless you saw where the OP is located in another post. How do you know which rating is better for him to use. His OD design temp could be 88.
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  11. #11
    Join Date
    Mar 2008
    Location
    Houston, Texas
    Posts
    352
    Quote Originally Posted by t527ed View Post
    hey i'm all growed up, let er rip........

    Most of the systems are rated in extreme heat, for example Arizona. As far as I'm concerned it wouldn't matter if they rated the equipment @ 110F or 150F because it is dry heat. If anyone has been outside in dry heat, they know it's hot, but that's about it. If you come down south (not an invite) you will see 80F that is worse than 110F for your body to handle. It has the same effect on an A/C system and in the process "your" seer rating is blown to hell because the equipment can't produce here.
    What good does it do to save money if the equipment can't perform? That is why "here" anything over 13 seer is almost a waste of time.
    Come visit the tropics of Houston....lol

  12. #12
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    Quote Originally Posted by Skip 2 my lou View Post
    If you come down south (not an invite)
    Since that isn't an invite, I'm not visiting.
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  13. #13
    Join Date
    Mar 2008
    Location
    Houston, Texas
    Posts
    352
    Quote Originally Posted by beenthere View Post
    Since that isn't an invite, I'm not visiting.

    Maybe one day someone will explain to me what a pellet stove is. I haven't used my heater in three years.

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