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  1. #1
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    Apr 2003
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    10 SEER to 13 SEER?

    What is the understanding within this Forum regarding the transition from 10 SEER to 13 SEER? Can a homeowner replace the condenser with a 13 SEER and leave the 10 SEER evaporator in place?

    I totally understand that the 13 SEER efficiency is lost if the indoor/outdoor SEER ratings are mis-matched. That is not my question. I am asking if the DOE has mandated that the indoor/outdoor components have the same SEER?
    "It's what you do when you don't have to that makes the difference when it counts."

  2. #2
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    Jan 2004
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    No, its just not legal for the manufacturer to sell equipment that does not have a 13 SEER match.
    You can by a 13 SEER condenser and legally put it on an 8 SEER evap coil as far as the Fed DOE reg is concerned. Local codes may not allow it.

    Another thing many people are confused about. Is they think that the 13 SEER condenser will just use more electric to do its X tonnage work. In reality, a 3 ton 13 SEER condenser hooked to a 10 SEER evap coil, may now be a 9 SEER 2.25 ton unit.
    You lose capacity, thats why you lose efficiency with those matches.
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  3. #3
    Join Date
    Apr 2008
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    Rochelle Il / Chicago
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    So what was the end result with the 13 seer? Compressors are smaller but coils are larger and this is how higher seer is achieved?

    Total dehumidification is less and this is why variable speed and two stage equipment is recommended. Not to mention hole house dehumidifiers or the Lennox humidatrole.

  4. #4
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    Unfortunately, the EPA, and DOE only looked at energy usage with tunnel vision.
    They gave no consideration to some people having to set their stats lower, to get the same comfort from some of the new units.
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  5. #5
    Join Date
    Apr 2008
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    Texas
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    63
    Quote Originally Posted by beenthere View Post
    In reality, a 3 ton 13 SEER condenser hooked to a 10 SEER evap coil, may now be a 9 SEER 2.25 ton unit.
    You lose capacity, thats why you lose efficiency with those matches.
    What is the basis for losing capacity? 25% Loss in Capacity? Where does that data come from?

  6. #6
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    That was from a test Bristol compressor did. they used a 3 ton HP. Tested it with both piston, and TXV.
    And they tested it in both heat and cool mode. they attempted adjustments to the charge.
    Someone posted the results, or a link to them. Just not sure what thread it was in, or who posted it.
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  7. #7
    Join Date
    Jun 2005
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    SW Wisconsin
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    We need to face a lot of reality factors that are not mentioned when talking about SEER ratings.

    This is only my opinion based on my experience as an HVAC tech since the mid 1970's.

    If you are in a hot high humidity climate you will want a very cold cooling cool coupled with long run cycles.

    In my opinion, the optimal return on your investment will probably be in reducing humid air infiltration & other factors that reduce the heatload!

    I would always demand that the system have a scroll compressor & a Thermostatic Expansion Valve (TXV) refrigerant metering device. In some cases that requires at least a 14-SEER rather than a 13-SEER system.

    "Regarding the 13-SEER condenser using a 10-seer cooling coil, if you live in a 'very hot high humidity climate' & the 10-seer coil has an adjustable superheat TXV refrigerant control;" you could set the Room Stat at 78-F & increase the airflow somewhat to get close to the condenser's BTUH Rating.

    With optimal air circulation in the rooms & the low humidity (45%) you would be well within the human comfort zone. (i.e., 50% RH 79-F)

    http://www.udarrell.com/air-conditio...tent-heat.html
    - Darrell

  8. #8
    Join Date
    Dec 2007
    Location
    East central Indiana
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    How about this strategy:

    Suppose the home owner has a 3 ton 10 SEER system (both coil and condenser). Now, my hunch is that if you replace the 3 ton 10 SEER with a 2.5 ton 13 SEER and use a suction line filter dryer (in addition to doing its job of filtering, it would also help flash any liquid that may be coming back to the compressor into gas), then everything should work out OK. I am, of course, assuming that the original 3 ton didn't run all the time to "keep up", so that the new 2.5 ton will just run a little bit longer to do the same job, and perhaps remove more humidity in the process. Any thoughts on this?

  9. #9
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    If the suction drier is flashing liquid to gas. Then the system has a problem, and the drier is restricting. And you don't have 2.5 tons of capacity.

    If the old 10 SEER system was moving the proverbial 400 CFM per ton. You now have high humidity, and maybe some mold growing in the ducts, and other areas of the house.
    Because the evap coil temp is too high.

    And, after mold remediation, you still need a new indoor coil or air handler.
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  10. #10
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    Dec 2007
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    East central Indiana
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    beenthere,

    Thank you for your response. Now, keep in mind, I'm no "master tech" (more of a "helper"), but I have a few questions about your post.

    If I understand what you're saying, the presence of liquid in the suction line would indicate that the system definitely has problems and is not operating to full capacity. This seems obvious enough. My intention with the "extra function" of the suction dryer is to add volume to the suction line to keep ANY of the tiniest drops of liquid from returning to the compressor. And my hunch is that there probably wouldn't even be any such liquid because the coil is 3 ton (albeit a 10 SEER).

    But, for kicks and giggles, let's suppose that the capacity of the unit has been reduced to 2 tons (for easy math). So, we now have a 2 ton unit with 1200 cfm moving across it. In general, at least in my area, this never causes too many problems. In fact, common match ups in my area are 75,000 BTU furnaces (with 3 ton blower drives) mated with 2 ton AC units. But, to play devil's advocate, this *new* "2 ton unit" will be running 50% longer than the old 3 ton unit, so my guess would be that, in terms of dehumidification, the longer running time would compensate for the lower degree differential.

    Or am I completely wrong? BTW, based on Copeland model numbers, it seems that a new 3 ton 13 SEER unit seems to use more or less the same compressor as an old 2.5 ton 10 SEER.

  11. #11
    Join Date
    Feb 2006
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    I posted that data from Bristol a year or so back. Do not remember the exact thread, but along with the testing results and graphs, it showed up to a 40% loss in cap. in clg., up to 48% in htg., up to 40% loss in efficiency in clg., and up to 60% loss in htg..
    Sound installation practices is the key to success. Equipment is only as good as the person installing it.

    If I can't fix it, it ain't broke.

  12. #12
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    Jan 2004
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    Newer units do use a small BTU rated compressor then 10 or 8 SEER units.
    They use large condenser and evap coils to get the BTU capacity.

    The furnace may have a 3 ton drive, but what is the actual CFM its moving?

    Just for explanation, lets say its moving 1200 CFM. And that the new condenser coil combo is 2 tons TOTAL capacity.

    Now, with 1200 CFM, the latent BTU is reduced to 2400 BTUs an hour, instead of the 5400 that is needed. So the house is gaining moisture faster then the A/C is removing it.

    So now the new unit is running almost 34 minutes to remove the same amount of moisture as the 3 ton would in 15 minutes. Plus not lowering the temp of the house.

    Suction filter driers don't add much to the volume of the vapor line. Unless your putting a drier in that is grossly over sized.
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  13. #13
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    Quote Originally Posted by TMH58 View Post
    I posted that data from Bristol a year or so back. Do not remember the exact thread, but along with the testing results and graphs, it showed up to a 40% loss in cap. in clg., up to 48% in htg., up to 40% loss in efficiency in clg., and up to 60% loss in htg..
    You mean this one.
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