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  1. #1
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    Determining Ideal Balance Points for VisionPro IAQ

    I've run spreadsheets full of calculation using the datasheets for the heat pump and determined my thermal and economic balance points based on my estimated heat loads for my home.

    Thermal Balance Points for each stage:

    1st stage HP: 35F
    2nd Stage HP: 24F
    1st Stage Gas: 7F
    2nd Stage Gas: -27F

    Economic Balnce point is a COP of 2.13

    First, my COP data is determined by using the data from the product and performance data using the installed furnace, coil and HP. Is the deforst cycle factored into the data. If so, how much should that reduce the COP?

    If the heating data includes defrost, (keep in mind while defrosting I'm using gas aux @ 2.13 not resistance at 1.0). Then the Economic Balance point is 18F, below my thermal balance point.

    My question is were should I set the 2 balance points (HP lockout temp and Aux lockout temp). I obviously want the run the HP as much as possible above the thermal balance point and rely on a 2F droop or 60 minute timer to automatically go to auxillary.

    My first thought was to use 24F for HP lockout and around 36F for the auxillary lockout. Then see how the system performs and adjust as nessesary.

    Am I better to err toward lower balance points (but above the economic BP)? One example is heating in the afternoon when there is more solar heat gain. The HP in that case could probably maintain temp below the calculated balance point.

    For reference:

    Trane 60k BTU XV80 (3 ton VS blower), 3 Ton XL16i, 4 Ton cased 410a "A" coil, 20x25 "Trion Air Bear Supreme" 5" media filter (MERV 8).

    Specifically: TUD060R9V3, 4TXCB48BC3, 4TWX6036C1

    One other question unrelated to balance point, are 4" snow legs on top of the regular 2" plastic base tall enough for SE Iowa? We get more snowfall than St Louis, MO and a little less than like Cedar Rapids, IA or Iowa City. The unit is sitting on the northern side of the home and the ground slopes away from the house near the unit. With almost 40" tall coils... what would happen if the bottom 3-4" were below snow level if we got a huge snowfall?

    The installers should be putting in the furnace tommorrow. The return duct and setting the condensor took them longer than expected.

  2. #2
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    Jan 2009
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    One other thought. If I use temp setbacks, then I should set 345 to 0 and use 60 minutes for 346? and then use a little less "aggressive" balance points?

    I get the feeling that I may need to try a few different setting, use it for a week and see what works best.


    I'm asking all of these questions because while I think my installer in competent and will set it up correctly, I don't think they use the IAQ or Trane XL900 enough on dual fuel set-ups to really optimize it to minimize energy useage while maintaining comfort. I'm not sure how well Trane covers this in their training.


    This post: http://hvac-talk.com/vbb/showthread....+points&page=3 does cover these questions pretty well... but i thought my set-up might warrant some different opinions.

  3. #3
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    One more question... I'm assuming the XL16i will innitiate the call for heat when it goes to defrost. Does it use just the 1st stage heat, or second stage? Also, does it delay starting the defrost for 30 or 45 seconds for the furnace to warm-up?

  4. #4
    Join Date
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    Lancaster PA
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    Set the HP to lockout a few degrees below its Economical BP.
    Set the furnace to lockout a few degrees above the HPs Economical BP.

    The balance point chart, doesn't allow for solar gain during the day.
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  5. #5
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    Quote Originally Posted by beenthere View Post
    Set the HP to lockout a few degrees below its Economical BP.
    Set the furnace to lockout a few degrees above the HPs Economical BP.

    The balance point chart, doesn't allow for solar gain during the day.
    You think that will still give good comfort with the IAQ internal logic even if in my situation where the economical BP is BELOW the thermal BP. Assuming hte thermal heat loss rate was calculated correctly.

  6. #6
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    The thermostat will probably bring on the furnace before you get to economic BP, because the house temp drop.
    No reason to let the temp drop lower then need be, to save 2 bucks a month.

    COP, is the heat output efficiency only, it has no allowance for defrost.

    HSPF does.

    A quick cheat you can use.
    Is take your HSPF, turn it into decimal. EG: HSPF = 9, make it .9
    Multiply that times your COP at temps that the HP will be able to go into defrost.

    EG: COP 2.5 X .9 = 2.25
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  7. #7
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    Quote Originally Posted by beenthere View Post
    The thermostat will probably bring on the furnace before you get to economic BP, because the house temp drop.
    No reason to let the temp drop lower then need be, to save 2 bucks a month.

    COP, is the heat output efficiency only, it has no allowance for defrost.

    HSPF does.

    A quick cheat you can use.
    Is take your HSPF, turn it into decimal. EG: HSPF = 9, make it .9
    Multiply that times your COP at temps that the HP will be able to go into defrost.

    EG: COP 2.5 X .9 = 2.25
    Thanks for the quick cheat! That's the first time I've seen that to use as an estimate. That certianly changes thing a little bit... unless NG prices jump again.

    Plugging that into my spreadsheet.... my economical BP is now 27F in first stage and 21F in 2nd stage. So what would you recommend? I'm thinking using 25F for the HP lockout and then 30F for the furnace lockout.

  8. #8
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    Those lock out temps sound good.
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  9. #9
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    Quote Originally Posted by beenthere View Post
    The thermostat will probably bring on the furnace before you get to economic BP, because the house temp drop.
    No reason to let the temp drop lower then need be, to save 2 bucks a month.

    COP, is the heat output efficiency only, it has no allowance for defrost.

    HSPF does.

    A quick cheat you can use.
    Is take your HSPF, turn it into decimal. EG: HSPF = 9, make it .9
    Multiply that times your COP at temps that the HP will be able to go into defrost.

    EG: COP 2.5 X .9 = 2.25
    Just an observation. The derating factor obtained with that method scales backwards from what it ought to. What I mean is that with that approach, given a hypothetical HSPF of 10 the adjusted COP would be equal to the listed COP. I.e., the derating factor obtained with your formula would be equal to 1. However, as HSPF increases, then the defrost cycle has more and more of a negative impact on efficiency, so the derating factor ought to increase as the HSPF increases.

    The general idea that you used here is fine, but the math doesn't quite work out. It would probably be easier to just subtract about 10% off of the listed COP at the given temps. The loss in COP would be greater in systems with higher HSPFs, which is at it should be. Or in other words use .9 nine as your COP derating factor regardless of HSPF.

  10. #10
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    COP loss wouldn't be greater with higher HSPF.

    Its not meant to be a 100% accurate method.

    Just a quick idea calc, to allow for defrost.

    You wouldn't use it at all for COPs that are for temps above defrost temps.
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  11. #11
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    My HSPF is 8.5, so I used .85. I'm happy with that. It still gets me down to 27F.

    Quite frankly, we're getting a little screwed and overchanrged in this part of Iowa, so I'd rather give my money to the gas company than the electric company. Even worse, they stopped reading meters every month and do a estimated reading every other month. So if I want accurate meter readings to compare year to year performance, I have to go outside and read it manually myself.

    The gas company apparently has the right equipment.

  12. #12
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    That bites.

    We have the newer meters here.
    They just drive close to your house, and download the reading.
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  13. #13
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    Quote Originally Posted by beenthere View Post
    That bites.

    We have the newer meters here.
    They just drive close to your house, and download the reading.

    That's what the gas company has. The electric company is in the process of adding that. A good friend used to be the guy that walked aroudn and red the meters (he moved to TX ) but said his job was going going away in the next year as they added the meters.

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