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  1. #14
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    Jan 2004
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    With new stats aimed at "Comfort", you will not always get run times over 10 minutes during the milder days.

    A 10 on 5 off, is a 4 CPH setting on a CPH stat. I prefer 3 CPH. Gets you either a longer on time, or a longer off time. Or combination of both.

    I don't undersize A/Cs, if its a border line 2, or 2.5 ton. I install 2.5 ton.
    I can slow the blower down to drop capacity in that case much easier then increasing cap on the smaller unit.

    It was never recommended to adjust or verify charge without letting the unit run for a min 15 minutes. Just a bad habit that many people did, and still try to do.

    If its 70* outside, and a customers A/C runs for 10 minutes to maintain a set temp 70* indoors, that is a long run time.

    I have never had a customer complain that the system held 72* when it was 95* outside. But customers do complain if the temp goes up to 78* when its 90* outside.

    You may undersize them to meet your personal efficiency requirements.

    I will size and install them to meet customer comfort requirements, After all. I sold them a system to make them comfortable. Not to meet my expectations of comfort or efficiency run times.
    That is why its important to offer choices of system types. (single or 2 stage, PSC or VS blower)

    Its like buying a car to drive long distances. You consider both MPG, and comfort of ride.
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  2. #15
    Join Date
    Aug 2003
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    Fort Worth, TX
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    Quote Originally Posted by beenthere View Post
    Its like buying a car to drive long distances. You consider both MPG, and comfort of ride.
    That's for sure. When I was a tall, thin, 24 year old I drove an '83 Nissan pickup clear across the country, from west coast to east. Got great mileage. Being 24, comfort wasn't a problem; I had just got off a ship where napping on steel decks was common just to get any sleep at all.

    Now, still tall but not as thin, comfort is more important for driving long stretches, and it's a challenge to find a vehicle that is both comfortable and doesn't need a refinery towed behind it to stay on the road. The '83 Nissan would definitely NOT be comfortable now, for certain, but if it's still on the road and well maintained, it's still likely getting good mileage!

  3. #16
    Join Date
    Aug 2003
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    466
    I do agree with the balance between comfort and efficiency and do agree that there are several ways to commit to this balance without undersizing directly with the system components. This balance of comfort and efficiency is why the two stage compressors that run continuosly while unloading capacity for lower needs is such an important tool for those of us in the industry to use. Still, systems need to be sized for the actual needs more so then just reliance on general load calculations that sometimes have buffer equations inbedded in them.

    For the reason of balancing comfort and efficiency I also feel that the variable speed blower technology is a major innovation in our industry. As mentioned, lower air flow can make up for shorter cycle times in respect to comfort control. Still, we need to design systems to operate for as long as we can get them to continuously operate in order to get the most out of the efficiency of the equipment. In keeping with the automotive analogy, it takes a lot more gas to ramp up to speed then it does to cruise.

  4. #17
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    Jan 2004
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    Lancaster PA
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    Agree with more energy to get to speed then maintain speed.

    But, have to be carefull when talking about efficiency and total energy consupmtion of an A/C.

    An A/C, draws highest amp during start up, for a second, then drops.
    Even though it may not be at full efficiency until it has ran for 15 minutes. Its actual efficiency for those first 15 minutes isn't all that low.
    Check the amp draw, its not high.
    And the electric bill won't show in the milder months won't be high enough that a 10% efficiency difference would even show for the average house.
    Lots of days were the OD temps are low enough that a 5 or 10 minute on time, and then not run for an hour, is normal, and a good thing.(hard time noticing the start cost on a month of that kind of operation.

    Take the LRA, and calculate the actual wattage consumed during the initial start of a compresser. Its not as high as you might think.


    So its not like bring a car from 0 to 60.
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  5. #18
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    Aug 2003
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    I am not trying to be argumentative. I am agreeing with your postings beenthere. I am also enjoying the banter to refine what we are both getting at from slightly different approaches.

    Yes, moments after initial start up the amp draw of the compressor and motors do reduce to pretty much what they will be throughout the rest of the system cycle. However, the amount of heat transfer during the next 15 minutes is constantly increasing. Therefore, just after the initial start up, the system may be drawing a reasonable amount of amps but the heat transfer per watt of energy is not as good as it should be and won't be until the system has run for a longer time. Since each minute of operation until the system reaches it's efficiency potential is itself more efficient, the shorter 10 minute cycles during milder days is still more efficient then a larger capacity system that would only run for 5 minute cycles.

    The ultimate efficiency would be a system that never shut down while maintaining to proper temperature. This is where staged systems come in. 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.

    Again, not trying to be argumentative. Just enjoying the vollying of knowledge and experience between professionals.

  6. #19
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    Aug 2003
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    Fort Worth, TX
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    Quote Originally Posted by everythingair View Post
    Still, systems need to be sized for the actual needs more so then just reliance on general load calculations that sometimes have buffer equations inbedded in them.
    Just curious...how are "actual needs" determined outside of a load calculation? What exactly are these "buffer equations" that might pad a load calculation one way or the other?

    For the reason of balancing comfort and efficiency I also feel that the variable speed blower technology is a major innovation in our industry. As mentioned, lower air flow can make up for shorter cycle times in respect to comfort control. Still, we need to design systems to operate for as long as we can get them to continuously operate in order to get the most out of the efficiency of the equipment. In keeping with the automotive analogy, it takes a lot more gas to ramp up to speed then it does to cruise.
    Long run times on a design day are from the tradition of a structure of marginal thermal efficiency. No intelligent discussion of a balance between comfort and efficiency can occur if the focus is only on equipment. The discussion must include the composition of the building envelope, and external/internal stresses working against the interior environmental conditions sought after.

    It happens every day...a customer is sold high efficiency/multi-staging a/c, which then is hooked up with kinked up flex duct, unsealed supply boots penetrating the attic floor/interior ceiling juncture, leaky supply and return plenums, unsealed return boxes in ceiling or unsealed chases in walls used as return chambers, attics with excessive heat gain (with no radiant barrier) adding heat to the snaking, meandering flex duct runs, unsealed can lights in ceilings, PAV's, minimal to no shading on eastern, southern, and western exposures of the structure, excessive infiltration, etc. etc. etc.

    Quality equipment/system design and selection + quality installation + thermally efficient building envelope = true balance between energy efficiency and personal comfort.

  7. #20
    Join Date
    Mar 2008
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    205

    Been, Shop, Everything: What I'm askin' is

    Quote Originally Posted by everythingair View Post
    I am not trying to be argumentative. I am agreeing with your postings beenthere. I am also enjoying the banter to refine what we are both getting at from slightly different approaches.

    Yes, moments after initial start up the amp draw of the compressor and motors do reduce to pretty much what they will be throughout the rest of the system cycle. However, the amount of heat transfer during the next 15 minutes is constantly increasing. Therefore, just after the initial start up, the system may be drawing a reasonable amount of amps but the heat transfer per watt of energy is not as good as it should be and won't be until the system has run for a longer time. Since each minute of operation until the system reaches it's efficiency potential is itself more efficient, the shorter 10 minute cycles during milder days is still more efficient then a larger capacity system that would only run for 5 minute cycles.

    The ultimate efficiency would be a system that never shut down while maintaining to proper temperature. This is where staged systems come in. 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.

    Again, not trying to be argumentative. Just enjoying the vollying of knowledge and experience between professionals.
    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.

  8. #21
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    Jan 2004
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    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.
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  9. #22
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    Yes, temp set back does save money.

    How much varies with amount of time the temp is set back, and how much.
    A 2* set back for an hour, is almost impossible to see any savings.

    A 4* set back for 6 hours, should yield 3% plus, depending on outdoor conditions during recovery.
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  10. #23
    Join Date
    May 2007
    Location
    Naples, Fl
    Posts
    889
    Romulan

    Will a conservative summertime setback program reduce the utility bill? A qualified yes goes here.

    Will the utility savings be offset by the increased starting and stopping of the equipment resulting in premature failure? Shophound touched on this with the house as a system reference. The better thermal/pressure envelop the less a vacant residence will require processed air. Be it cooled or dehumidified. So the resultant CPH could be fewer or just as many but shorter compared to no setback.

    Sitting in a cubicle somewhere is a person that has the answer to the question will summertime setback result in a negative impact on run time to failure.

  11. #24
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    Jun 2007
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    Quote Originally Posted by everythingair View Post
    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.
    I thought that 2 stage systems had a higher EER on 1st stage than 2nd stage, thus the high SEER# for 2 stage condensers?

  12. #25
    Join Date
    Aug 2003
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    466
    Quote Originally Posted by shophound View Post
    Just curious...how are "actual needs" determined outside of a load calculation? What exactly are these "buffer equations" that might pad a load calculation one way or the other?



    Long run times on a design day are from the tradition of a structure of marginal thermal efficiency. No intelligent discussion of a balance between comfort and efficiency can occur if the focus is only on equipment. The discussion must include the composition of the building envelope, and external/internal stresses working against the interior environmental conditions sought after.

    It happens every day...a customer is sold high efficiency/multi-staging a/c, which then is hooked up with kinked up flex duct, unsealed supply boots penetrating the attic floor/interior ceiling juncture, leaky supply and return plenums, unsealed return boxes in ceiling or unsealed chases in walls used as return chambers, attics with excessive heat gain (with no radiant barrier) adding heat to the snaking, meandering flex duct runs, unsealed can lights in ceilings, PAV's, minimal to no shading on eastern, southern, and western exposures of the structure, excessive infiltration, etc. etc. etc.

    Quality equipment/system design and selection + quality installation + thermally efficient building envelope = true balance between energy efficiency and personal comfort.
    Once again, there is no argument here. Actually, the second part of this post answers the question of the first part of this post.

  13. #26
    Join Date
    Feb 2007
    Posts
    999
    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.


    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?
    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

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