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  1. #1
    Join Date
    Aug 2008
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    107

    SEER and EER on higher tonnage units

    Can someone explain to me why lower level product lines tend to outperform the high end lines on higher ton systems? It seems like the Carrier Performance 16 outperforms the infinity systems at higher ton ratings. Is it because of the two stage system in the infinity. The infinity system doesn't even get to 17 SEER in their 5 ton size. If Trane comes out with a tax credit eligible unit, someone said it will be in the xr series. When it comes to higher tonnage units, I guess it is all about comfort and not energy savings if you want to go with the top tier product lines.

    What are the best performing 5 ton systems out there? It seems like the Trane xl20i is one of the best exceeding 17 SEER and having an EER of 11.5. It seems like it almost meets the tax credit criteria. It would just need to bring up its EER by 1. Does anyone think they will be able to do this in the near future? I'm referring to a variation of the 20i.

  2. #2
    Join Date
    Aug 2004
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    North Richland Hills, Texas
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    14,914
    2 stage equipment kinda gets screwed by the EER requirement since it only accounts for steady state operation in 2nd stage. The EER in 1st stage is usually very high, but it is not factored into the ratings at all.

    5 ton equipment is a challenge too. There is only so far they can reasonably go with coil sizes.
    There is also a balance between the raw efficiency of a system and its real world performance as a comfort system.
    While I've only looked at the performance data for two different 5 ton systems that qualify under the current tax credit program, neither one of the systems are something I'd recommend to someone in a humid climate.

    Somewhere in all this fuss about energy efficiency and tax credits, some people seem to have forgotten that there is more to comfort than lowering the temperature of the air.
    If more government is the answer, then it's a really stupid question.

  3. #3
    Join Date
    Aug 2002
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    Office and warehouse in both Crystal River & New Port Richey ,FL
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    18,836
    Carrier now has the Comfort 16 two stage,others coming soon in 2 thru 5 ton,tax credit units.

    Larger tonage has always tended to be lower SEER,size (keeping indoor and outdoor units to a size that will fit) is likely one of the issues.

    The Infinity outdoor cabinet has one side devoted to service access,the Comfort has "coil" on all four sides,more coil,better air flow from the fan,higher ratings are easier to obtain.

  4. #4
    Join Date
    Apr 2008
    Location
    Northwest Arkansas via Chicago Area via Straight Up from There on Lake Superior
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    1,411
    Quote Originally Posted by mark beiser View Post
    2 stage equipment kinda gets screwed by the EER requirement since it only accounts for steady state operation in 2nd stage. The EER in 1st stage is usually very high, but it is not factored into the ratings at all.

    5 ton equipment is a challenge too. There is only so far they can reasonably go with coil sizes.
    There is also a balance between the raw efficiency of a system and its real world performance as a comfort system.
    ...
    So, Mark, are you saying, all of this tax credit mess aside and its requirement to rate it at max stage 2, that a unit that runs a lot in stage 1 will actually cost less than the apparent numbers measured at stage 2?

    My new 2-stage York HP with modulating furnace, which doesn't have the furnace hooked up yet and the tstat isn't fine-tuned, appears to be much more comfortable than the old 1-stage, on/off, split AC/furnace. Love it! But I am also hoping for a nice cut in energy cost going from a 10-SEER AC to an 18-SEER HP. Less than a week after the initial turn on, the electric co-op announced a request for a rate hike. Here we go, Pres!

  5. #5
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
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    Quote Originally Posted by jerryd_2008 View Post
    So, Mark, are you saying, all of this tax credit mess aside and its requirement to rate it at max stage 2, that a unit that runs a lot in stage 1 will actually cost less than the apparent numbers measured at stage 2?
    In short, yes. At least it will regarding the EER rating.
    The SEER rating already somewhat accounts for 2 stage operation, but SEER is a bit of a smoke and mirrors rating anyway IMO.

    This is assuming that the duct system is tight and well insulated of course. Leakage from ducts and heat gain from inadequate duct insulation are a much bigger issue with 2 stage equipment than with single stage equipment. Leakage and heat gain in the ducts can cripple 1st stage due to the longer run times and lower air velocities through the ducts.

    Neither rating is all that good of a real world indicator, but they are all we've got, so we have to live with it.
    If more government is the answer, then it's a really stupid question.

  6. #6
    Join Date
    Jun 2005
    Location
    SW Wisconsin
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    4,975

    Innate Problems Apart From Ratings

    A major problem, totally apart from their ratings, is with the much higher indoor airflow demands through the coil of tonnages of 4 & 5 ton.

    Consider, how many 3.5 to 5-Ton units (even down to 1.5-Ton'ers) have the required airflow through the indoor coil?

    That is just one of the problems with the larger tonnage units... - Darrell

  7. #7
    Join Date
    Apr 2008
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    Northwest Arkansas via Chicago Area via Straight Up from There on Lake Superior
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    Quote Originally Posted by udarrell View Post
    A major problem, totally apart from their ratings, is with the much higher indoor airflow demands through the coil of tonnages of 4 & 5 ton.

    Consider, how many 3.5 to 5-Ton units (even down to 1.5-Ton'ers) have the required airflow through the indoor coil?

    That is just one of the problems with the larger tonnage units... - Darrell
    Darrell, I will apply a similar question to your airflow issue with 4-ton and above units. If the 2 stage compressor and VS furnace run a much reduced airflow most of the time, then even big units will blow slower across the coil and better utilize the cooling/heating capacity, right? Seems to imply lower operating costs for "higher" (got to look at credits, rebates, warranties, etc.) up front costs.

    PS: I have a new 4-ton, 18 SEER, 2-stage HP with an 80%, VS, modulating furnace and smart Honeywell VisionPro IAQ tstat.

    Thanks, Mark.

  8. #8
    Join Date
    Jun 2005
    Location
    SW Wisconsin
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    jerryd_2008,
    My only point would be, that you want the blower to deliver the CFM airflow that will properly match the compressor's 1st or 2nd stage BTUH output to the sensible/latent ratio that's most desirable for your specific local humidity level conditions.

    You guys know more what you can do in this regard than I do, as you work with that equipment, I've been retired too long to have that on-hands experience.

    Proper airflow through the evaporator coil is critical regarding EER & SEER efficiency & nominal BTUH performance. - Darrell

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