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  1. #27
    Join Date
    Aug 2003
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    466
    Quote Originally Posted by RomulanSpy View Post
    do we save $$$$ by cutting the T-stat up into the 80's while we're gone to work or just at the pool chillin'?

    The OD here in Dixie exceeds 90 most everyday from June til mid September. So the ID temp gets toasty but we're not here to not enjoy it. But when we're getting ready to settle in for the night we get it down to a comfy 70*

    Then it cycles on/off all night to maintain the comfy temp.

    Now when it cycles on in the late afternoon to bring the temp down to the lower 70's the A/C runs continuously for at least 3 hours, then shuts down and begins the cycling.

    Just wondering if this is the BEST way to keep compressor good and more mullah in the bank. And yes, when the ID temps hits the lower 70's the RH is at a very comfy level, despite our ancient of days Armstrong 10 SEER straight AC.
    Cooling needs and operations vary more then heating needs and operation depending on the type of climate an individual system is operating in. One of the most disturbing problems with trying to pin down the "best" method of cooling and the "best" way to save money on energy is the fact that what is best for one area of the world is not always best for another, and if fact can actually be detrimental in another.

    If you live in a very high humidity clime, it is not a good idea to increase the thermostat temperature in the cooling mode if you are only going to be setting it back for a few hours at a time. The higher the temperature of the structure goes, the more humidity is allowed into the air that will also permeate walls, floors and furnishings. The amount of energy saved over a brief period will be overwelmed by the amount of additional energy it will require in order to remove the additional moisture that was allowed into the dwelling during the rise in temperature period.

    In humid areas, I suggest not setting thermostats to a higher temperature unless the dwelling is going to be unoccupied for more then 48 hours. In dryer parts of the world, the thermostat can be set up for any period of away time and will save energy for the lack of usage during that time.

  2. #28
    Join Date
    Aug 2003
    Posts
    466
    Quote Originally Posted by beenthere View Post
    The problem in the industry. Is there is no clear cut industry wide definition of oversized, or undersized.

    Just the interpretation of the individual.
    To me, if its 2,000 BTUs short of capacity at design temps, its undersized.
    While if its 4000 BTUs more capacity then required at design, its not oversized, because the next smaller unit wouldn't meet capacity.

    But many won't agree with that. And as long as they are satisfing their customers, thats ok.

    No aurgument, just the way things are.
    Our limitations of equipment sizing is exactly why professionals who take all application needs into consideration should be the ones sizing system equipment components.

  3. #29
    Join Date
    Aug 2003
    Posts
    466
    Quote Originally Posted by gary_g View Post
    I thought that 2 stage systems had a higher EER on 1st stage than 2nd stage, thus the high SEER# for 2 stage condensers?
    Multiple staging is always for comfort purposes, not efficiency purposes, unless we are talking about the inverter technology that is making it's run in the HVAC industry. Efficiency is based on how much energy is used in order to transfer a certain amount of heat energy. A system that is operating at a lower capacity then the overall design of the heat transfer media is not going to transfer as much heat per square inch of heat transfer media in a lower capacity operation. The greater the temperature differential, the greater the heat transfer ratio.

    There are so many issues with dehumidification with more efficient systems utilizing larger coils that staging these systems to operate at lower capacities and lower blower speeds allows these higher efficiency systems to operate in such a manner that they improve the dehumidification during the lower stages of operation.

  4. #30
    Join Date
    Aug 2003
    Posts
    466
    Quote Originally Posted by ampulman View Post
    Quote:
    Originally Posted by everythingair
    However, if since staged systems run a bit less efficient on lower stages (same amount of energy to operate system components for less capacity of heat transfer), it is very important to not oversize staged systems as well.




    Maybe so, but in practical terms, when my a/c runs in 1st stage, both the compressor and the blower are running slower than when in 2nd stage == lower amps == lesser energy.

    AM
    And less Btu of heat transfer per watt of energy used.

  5. #31
    Join Date
    May 2007
    Location
    Naples, Fl
    Posts
    889
    Everything

    One man's high humidity is another man's design conditions. The question I have is; is the structure getting all water logged with the set back? It's not uncommon for us to go into a vacant (seasonal) home where the a/c has failed and the temps are over 90F but the RH (not absolute) is in the low/mid 40's. Is the humidity less because of the warmer air will hold more vapor? Which is the way it's taught or is the mositure in the structure? And if the RH is lower with the warmer temps where does the structure get the moisture from that it doesn't get when the humidity is higher under normal operating conditions. Or does the vapor content of the surrouinding air have nothing to do with it?

    Again back to the house as a system. Unoccupied house, no cooking, no cleaning, and no humans with a good pressure and thermal barrier in place.

  6. #32
    Join Date
    Jun 2007
    Location
    The Twilight Zone
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    2,964
    Quote Originally Posted by everythingair View Post
    And less Btu of heat transfer per watt of energy used.
    So 1st stage would have lower EER than 2nd stage, but it is the opposite. 1st stage has a higher EER than second stage. EER = system btu / condenser power draw in watts. High EER on 1st stage is the reason why dual condenser systems have a high SEER#.

  7. #33
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    Quote Originally Posted by everythingair View Post
    And less Btu of heat transfer per watt of energy used.
    Trane 2TTX9036A1, 3.0 ton XL19i two stage. Assume for simplicity that outdoor temperature is 95F, indoor wet bulb is 69F. Indoor dry bulb according to Trane documentation has no effect on total capacity(!), it just changes the balance between sensible and latent.

    1st stage: 19,700 btuh capacity, 1,200 watts. 16.4 btuh/watt
    2nd stage: 35,200 btuh capacity, 2,850 watts. 12.4 btuh/watt

    According to this Trane document, it is the low stage which has the better cooling efficiency.

    Best wishes -- Pstu

  8. #34
    Join Date
    Jun 2008
    Posts
    63

    Read the meter

    Quote Originally Posted by everythingair View Post
    Cooling needs and operations vary more then heating needs and operation depending on the type of climate an individual system is operating in. One of the most disturbing problems with trying to pin down the "best" method of cooling and the "best" way to save money on energy is the fact that what is best for one area of the world is not always best for another, and if fact can actually be detrimental in another.

    If you live in a very high humidity clime, it is not a good idea to increase the thermostat temperature in the cooling mode if you are only going to be setting it back for a few hours at a time. The higher the temperature of the structure goes, the more humidity is allowed into the air that will also permeate walls, floors and furnishings. The amount of energy saved over a brief period will be overwelmed by the amount of additional energy it will require in order to remove the additional moisture that was allowed into the dwelling during the rise in temperature period.

    In humid areas, I suggest not setting thermostats to a higher temperature unless the dwelling is going to be unoccupied for more then 48 hours. In dryer parts of the world, the thermostat can be set up for any period of away time and will save energy for the lack of usage during that time.
    Very true! This matches exactly what I experienced in Humid Houston.

    The 'setup while out' worked until the temps went to the mid 90's. At those temps and normal stat settings, I have a 30min on/ 30min off cycle time. Like Romulan, I also keep my house at low 70* while sleeping. My AC doesn't come on until around noon and runs 2 1/2 hrs until 5pm. If I 'setup while out' the AC runs 3-4 hrs to catch up.

    Romulan should try different plans for several days, and READ THE ELECTRIC METER. Then he will know what saves the most for him. A surprise to me was changing the SPAN setting to the lowest setting (more cycles) made a 10kwh/day difference. Your mileage may vary.

    Theoretical discussions can give you ideas to try, but only the electric meter knows the truth for your situation.

  9. #35
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,296
    Quote Originally Posted by pstu View Post
    Trane 2TTX9036A1, 3.0 ton XL19i two stage. Assume for simplicity that outdoor temperature is 95F, indoor wet bulb is 69F. Indoor dry bulb according to Trane documentation has no effect on total capacity(!), it just changes the balance between sensible and latent.

    1st stage: 19,700 btuh capacity, 1,200 watts. 16.4 btuh/watt
    2nd stage: 35,200 btuh capacity, 2,850 watts. 12.4 btuh/watt

    According to this Trane document, it is the low stage which has the better cooling efficiency.

    Best wishes -- Pstu
    Real world outcome of any two stage system is how well the equipment/controls/staging are configured for the home and climate where it operates, and the quality of the installation.

    Payson once made a post regarding two stage systems in Phoenix, AZ that were improperly configured, bouncing in and out of 2nd stage under stressful weather conditions. Even superficially reviewing that scenario would lead one to think that customer was paying a penalty for energy use, aside from his discomfort complaints.

  10. #36
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    I'm scratching my head over this one. You would not agree that low is low, and high is high, and that install problems don't turn low into high? What am I missing here?

  11. #37
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,296
    Quote Originally Posted by pstu View Post
    I'm scratching my head over this one. You would not agree that low is low, and high is high, and that install problems don't turn low into high? What am I missing here?
    Two stage systems that use two compressors, in residential applications, typically have a delay time where the smaller capacity compressor shuts off and the larger capacity compressor engages. During this delay period, say around a minute, the indoor blower keeps running while waiting for the 2nd stage compressor to engage. If ductwork is in the attic, as it so often is in hot climates (humid or dry), air moving through the ducts will be picking up heat from the attic that transfer through the duct insulation and walls, as it does with the blower on, compressor running or not. The difference is with the compressor off, there's around a minute where the house may gain heat from the supply registers (and usual heat gain sources) vs. staying more stable until high stage kicks on and stabilizes. This may not amount to much, but it is heat the system will need to remove, prolonging run times of the 2nd stage, which has a lower btu/watt efficiency. In humid climates, air blowing off the coil while the compressors are off will re-evaporate moisture into the airstream until either the compressors re-engage or the coil is dry. May not be much in a minute's time, may be more if there are return air leaks from a non-conditioned source (i.e. attic or crawl space).

    Also, every time the compressors transition between stages, there's the initial inrush current to start each one. If the interval between stages is too close, where the compressors are bouncing between 1st and 2nd stages, that's a lot of start/stopping occurring, vs. leaving one stage or the other engaged for longer time periods. Additionally, after a compressor starts, the refrigeration circuit efficiency takes a bit to re-establish itself, meaning reduced efficiency until enough time has passed for this to occur. The numbers you quoted were likely from steady-state operation measured for each stage, with stable return and outdoor ambient conditions established for the observation.

  12. #38
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,760
    A Copeland 2 stage compressor does use less wattage in first stage then in second stage. And it does remove more BTUs per watt then in second stage most times. (to lazy to pull up the specs of one and post it)

    The Trane 19i is probably the best set up for 2 stage with the 2 compressors( and I'm not even a member of the Tranewashed ) condenser wise.

    Not sure of the delay time on them for switching, but it too trivial to make enough of a difference.

    The Bristol TS can be reversed after several seconds. ( I think Carrier runs a longer delay then York did though )

    Start wattage is not as great as you might think. ( this should get some talk going )
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  13. #39
    Join Date
    Mar 2008
    Posts
    205

    I'm always tryin new stuff.

    Quote Originally Posted by jax1 View Post
    Very true! This matches exactly what I experienced in Humid Houston.

    The 'setup while out' worked until the temps went to the mid 90's. At those temps and normal stat settings, I have a 30min on/ 30min off cycle time. Like Romulan, I also keep my house at low 70* while sleeping. My AC doesn't come on until around noon and runs 2 1/2 hrs until 5pm. If I 'setup while out' the AC runs 3-4 hrs to catch up.

    Romulan should try different plans for several days, and READ THE ELECTRIC METER. Then he will know what saves the most for him. A surprise to me was changing the SPAN setting to the lowest setting (more cycles) made a 10kwh/day difference. Your mileage may vary.

    Theoretical discussions can give you ideas to try, but only the electric meter knows the truth for your situation.
    I'll give it a shot for next week. Wanna check the meter Tue-Sat then do the same for next week.

    Thanx

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