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  1. #1

    SEER effect on cooling time?

    A couple weeks ago, my upstairs 13 yr old 10 SEER York finally died. We'd done lots of patchwork fixes on the condenser last summer, but decided to replace the unit after the compressor failed during early summer here in DFW. I got a few quotes, and decided to go with a new 13 SEER Trane condensor and coil, leaving the furnace as it was recommended not to replace (still working fine).

    During the day when we're not home, I keep the upstairs at 85 deg until 4:30pm when I bring it to 78. On an average day, say 95 deg outside or so, our old unit used to be able to bring it down to 78 in about 3-3.5 hours. I noticed with the new unit that it takes longer, maybe 4.5-5 hours until it reads 78. A few questions:

    1) Does a higher SEER efficiency mean faster cooling, or just more efficient cooling?
    2) Would a new t-stat help operation in any way? (still on old one that came with the house)
    3) This was a switch from r22 to r410a. Does that matter in any way?

    Hopefully I'm asking the right questions. Thanks for any/all help.

  2. #2
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    1,934
    1) Does a higher SEER efficiency mean faster cooling, or just more efficient cooling?
    More efficient

    2) Would a new t-stat help operation in any way? (still on old one that came with the house)
    No

    3) This was a switch from r22 to r410a. Does that matter in any way?
    Capacity is capacity (size) so no.

    Just because you had new equipment installed that was the same size as the old equipment doesn't mean that the installation was done correctly or that there isn't some issue with the new system that needs attention.

    You should call the installer and tell them exactly what you asked here and get their response. They are the ones that can physically check the installation to make sure that the new system is working up to it's full potential and specifications.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  3. #3
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,086
    There are many ways manufacturers can tweak system combinations to achieve SEER ratings. I'm not a big fan of SEER as it isn't practically field measurable, and is assigned to a system in a controlled lab setting. Not real world. On any given day a tech can't pull up to your house with an instrument or two and easily derive if your system is operating at its rated SEER. At least with cars these days, the onboard computers can give you real time fuel mileage.

    That said, one way manufacturers tweak things to achieve a given SEER rating is to oversize the condenser and evaporator coils relative to the compressor's actual pumping capacity. IOW, your system can be rated at a nominal three tons, for example, but the compressor size is actually several thousand BTUH less. The somewhat smaller compressor will use less power to achieve close to the same cooling capacity, due to the oversized coils. The catch is that the indoor coil will run warmer, meaning it dehumidifies and removes sensible heat more slowly than a colder coil would.

    What few people realize is that the only time a three ton system actually moves three tons of heat out of a house is when it operates under the same test conditions in place when it got its ton rating from ARI. And that also would be with a perfect duct system, a feat near impossible in most houses today.

    One thing I would recommend to you is to lower your setback temperature from 85 to 82 or even 80. Seven degrees is a wide pulldown spread, and you're wanting that to occur at the worst time of day, when it's hot outside and the condenser must work harder to dump heat. Most people pick setback points arbitrarily...they don't ever really measure to see if the setback time span is offset by the pulldown time in terms of energy saved vs. energy consumed.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  4. #4
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    The biggest factor may be the simple fact that it is significantly more humid so far this year than it was this time last year, or the year before.
    Higher humidity levels can/will add greatly to the run time needed to lower the temperature in the house.
    If more government is the answer, then it's a really stupid question.

  5. #5
    Join Date
    Aug 2010
    Location
    West Monroe, LA
    Posts
    1,442
    Same size system are you sure? What I mean is this. One manufactors equipment might be rated at (3) tons but comes up a few thousand btu short compaired to your old equipment that might also be (3) but btu's are closer to the size.

    This is why important to do load cal manual j, then a manual s. The load cal determines how much heat gain and lose this part of the home needs. Manual s shows the contractor what equipment is needed to achive this.

    Just something to think about. I would not suggest set backs that aggressive or at all specialy with a upstairs system. Find you a set temp that is comfortable and let it work to reach that temp and maintain it. If sized propely should run 80-85% of that time with average temps to maintain the temp and on above average cooling days should be ruining most of the day to maintain the temp. Of course with a load cal you have to pick and choose your temp to design the load for any home. The most common Is 75 degree with 50% humdity with your average summer temp fit your area. Mine is 95.

  6. #6
    Quote Originally Posted by Shophound View Post
    There are many ways manufacturers can tweak system combinations to achieve SEER ratings. I'm not a big fan of SEER as it isn't practically field measurable, and is assigned to a system in a controlled lab setting. Not real world. On any given day a tech can't pull up to your house with an instrument or two and easily derive if your system is operating at its rated SEER. At least with cars these days, the onboard computers can give you real time fuel mileage.

    That said, one way manufacturers tweak things to achieve a given SEER rating is to oversize the condenser and evaporator coils relative to the compressor's actual pumping capacity. IOW, your system can be rated at a nominal three tons, for example, but the compressor size is actually several thousand BTUH less. The somewhat smaller compressor will use less power to achieve close to the same cooling capacity, due to the oversized coils. The catch is that the indoor coil will run warmer, meaning it dehumidifies and removes sensible heat more slowly than a colder coil would.

    What few people realize is that the only time a three ton system actually moves three tons of heat out of a house is when it operates under the same test conditions in place when it got its ton rating from ARI. And that also would be with a perfect duct system, a feat near impossible in most houses today.

    One thing I would recommend to you is to lower your setback temperature from 85 to 82 or even 80. Seven degrees is a wide pulldown spread, and you're wanting that to occur at the worst time of day, when it's hot outside and the condenser must work harder to dump heat. Most people pick setback points arbitrarily...they don't ever really measure to see if the setback time span is offset by the pulldown time in terms of energy saved vs. energy consumed.
    That's interesting and I wonder how I can tell. I've got the serial numbers of the new units but I guess without the old condenser and coil serials, its impossible to compare.

    Regarding the pulldown, are you saying then that its better for the A/C to cycle on/off more often throughout the day, maintaining a lower temp, than to have it run continuously once 4:30pm hits? I've read that having a unit cycle on/off uses more power than just to have it on and working, but I guess its kind of a common sense question which I've never been able to figure out.

  7. #7
    Quote Originally Posted by mark beiser View Post
    The biggest factor may be the simple fact that it is significantly more humid so far this year than it was this time last year, or the year before.
    Higher humidity levels can/will add greatly to the run time needed to lower the temperature in the house.
    Could be...I just feel like before the old unit kicked the bucket, it was cooling faster. Impossible to empirically determine at this point though.

  8. #8
    Quote Originally Posted by firecontrol View Post
    1) Does a higher SEER efficiency mean faster cooling, or just more efficient cooling?
    More efficient

    2) Would a new t-stat help operation in any way? (still on old one that came with the house)
    No

    3) This was a switch from r22 to r410a. Does that matter in any way?
    Capacity is capacity (size) so no.

    Just because you had new equipment installed that was the same size as the old equipment doesn't mean that the installation was done correctly or that there isn't some issue with the new system that needs attention.

    You should call the installer and tell them exactly what you asked here and get their response. They are the ones that can physically check the installation to make sure that the new system is working up to it's full potential and specifications.
    Thanks...I plan to observe for a week, and if its still not working well I'll reach out to them.

  9. #9
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,471
    Shophound's post #3, hits the nail on the head.

    There are some sacrifices made to get a lower wattage draw...electric power companies wanted legislation that would help reduce the peek-load so they wouldn't have to spend a ton of money expanding their capacity; they got what they wanted.

    The 10 & 12-SEER systems should NOT have been outlawed; there are many other more effective ways to make the home & the duct system more efficient in both heating & cooling modes. Consumers could more easily afford those units, which would have resulted in them being better enabled to make their home & other subsystems much more efficient.

    They are talking about different codes for different climate areas; wish they would let us & the consumers have wider efficiency choices.

    Got a phone call that's distracting me too much...

  10. #10
    Thanks for the input from all. I think what Shophound describes may be what's going on in my case; today I had it set for 78 the entire day, but late in the afternoon (~6pm) I noticed it go to 80 while the A/C ran continuously. That's telling me it can't keep up with the heat (95 deg day here in DFW today). I'm going to schedule them back out to see what they can do.

  11. #11
    Join Date
    Feb 2013
    Location
    Sonora, California, United States
    Posts
    797
    just out of curiosity was the old condensor and coil bigger then the new one?.....

  12. #12
    No, both are 4-ton units.

  13. #13
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    66,801
    may not be properly charged.
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