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  1. #40
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    Aug 2007
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    7
    The Liquid line contains the bulk of the refrigerant in the system supplying the metering device with the correct amount of refrigerant. Instead of capacity loss I would be more concerned with refrigerant vilocity and therefor oil return to the compressor.

  2. #41
    Join Date
    Nov 2007
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    47
    Quote Originally Posted by RoBoTeq View Post
    All ratings are under ideal lab conditions. Trying to nitpick about capacities and efficiencies can drive you crazy for absolutely no gain. Every time you turn your system on it changes efficiency and capacity statistics (unless you know for a fact that the voltage in your home is constant and you change your filters between every start up).
    So at what point do they become significant? 5%? 10%? 15%?

    The chart on page 45 that I referenced had a capacity reduction range between 3-22% when using a smaller than optimum suction line. The above question stated differently: Which capacity reductions in the chart are significant reductions?

    TLY

  3. #42
    Join Date
    Nov 2000
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    Eastern PA
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    68,943
    Quote Originally Posted by TLY View Post
    So at what point do they become significant? 5%? 10%? 15%?

    The chart on page 45 that I referenced had a capacity reduction range between 3-22% when using a smaller than optimum suction line. The above question stated differently: Which capacity reductions in the chart are significant reductions?

    TLY
    Personally I always try to put in what the manufacturer calls for even though that could change from one month to the next on the same exact system. If it just can't be done and you need to use a smaller line I would make 5% my personal limit. If you can afford to lose more then 5% capacity, you have grossly oversized the system anyway.

    These data sheets should be used as common sense guidelines not for the sake of arguing what is too much or too little. Do it as right as you can but don't nitpick over a few data points.

    This kind of rhetorical arguing reminds me of the contractors who claim that spending 2 hours on gathering data for a load calc is so much better then the company that does a very general load calc. In the end, the 21,232 Btu load calculated by the longer load calc is going to require exactly the same sized system as the 23,000 Btu load calc that was done with less specific data is going to require. Why spend more energy on something that is not going to matter in the long run? And by the way, that is between a 7-8% difference.

    Go ahead and worry yourself to death over a half a SEER point or 1,000 Btu capacity only to completely change the settings after the install in order to get better comfort from a system. It just don't make sense to obsess over minute data on a system that has so many variables.
    Last edited by RoBoTeq; 02-02-2008 at 02:12 AM.
    Government is a disease...
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  4. #43
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    18,836
    1.) "If you can afford to lose more then 5% capacity, you have grossly oversized the system anyway."

    36,000 btu system is 16% larger then 30,000 btu systm,more then 5% oversize their and the 36,000 one was still the only correcct size.

    2.) "In the end, the 21,232 Btu load calculated by the longer load calc is going to require exactly the same sized system as the 23,000 Btu load calc that was done with less specific data is going to require."

    The above can be true,but many times it the detailed calc would be 23,000 and the less specific would be 24,782,causing the equipment to oversized by half a ton.

    All the numbers used are just for this example,as we all know the actual numbers vary between brands and models and seldom match true ton or half ton btus.

  5. #44
    Join Date
    Nov 2007
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    47
    Quote Originally Posted by RoBoTeq View Post
    Personally I always try to put in what the manufacturer calls for even though that could change from one month to the next on the same exact system. If it just can't be done and you need to use a smaller line I would make 5% my personal limit. If you can afford to lose more then 5% capacity, you have grossly oversized the system anyway.

    These data sheets should be used as common sense guidelines not for the sake of arguing what is too much or too little. Do it as right as you can but don't nitpick over a few data points.

    This kind of rhetorical arguing reminds me of the contractors who claim that spending 2 hours on gathering data for a load calc is so much better then the company that does a very general load calc. In the end, the 21,232 Btu load calculated by the longer load calc is going to require exactly the same sized system as the 23,000 Btu load calc that was done with less specific data is going to require. Why spend more energy on something that is not going to matter in the long run? And by the way, that is between a 7-8% difference.

    Go ahead and worry yourself to death over a half a SEER point or 1,000 Btu capacity only to completely change the settings after the install in order to get better comfort from a system. It just don't make sense to obsess over minute data on a system that has so many variables.
    I can see where you think this is all rhetorical blabber just for the sake of argument...but it really isn't for me. We have very real and significant cooling problems that are going to be corrected by our contractor and I just want to make sure the right correction is made. Maybe by sharing some details of my problem it will become less rhetorical and more real.

    Our contractor is going to change out our 3.5 ton heat pump with a 4 ton heat pump to correct our cooling problems. The suction line is 7/8'' o.d. Our basement is finished, but the lineset has a straight line access to the exterior (50 ft.). I guess my question becomes do I insist that the lineset be replaced with the heat pump? To answer this, BTU's need to be considered in order to make a sensable decision. Well, here are my BTU options:

    3.5 ton HP (40,000 Btuh)+7/8'' line(3%loss) = 38,800 Btuh
    3.5 ton HP (40,000 Btuh)+1-1/8'' line(0%loss) = 40,000 Btuh
    4 ton HP (45,000 Btuh)+7/8'' line(4%loss) = 43,200 Btuh
    4 ton HP (45,000 Btuh)+1-1/8'' line(0%loss) = 45,000 Btuh
    5 ton HP (55,000 Btuh)+7/8'' line(7%loss) = 51,150 Btuh

    Do I let them change the HP without changing the line? At what Btuh load calculation do I insist on a new unit and line? Over 43,200? See, this is a very real problem, not rhetorical.

    TLY

  6. #45
    Join Date
    Aug 2002
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    Office and warehouse in both Crystal River & New Port Richey ,FL
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    No loss is obviously better,can the lineset be changed?If it's major cost,then it might not be worth it.

    How will you know that the load calculation is accurate,to decide which size and loss to select?


    How about adding some insulation,to reduce the size system needed,so the lineset will be the right size?If possible that will save you more ,then the cost of changing the lineset.

  7. #46
    Join Date
    Nov 2007
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    47
    Quote Originally Posted by dash View Post
    No loss is obviously better,can the lineset be changed?If it's major cost,then it might not be worth it.

    How will you know that the load calculation is accurate,to decide which size and loss to select?


    How about adding some insulation,to reduce the size system needed,so the lineset will be the right size?If possible that will save you more ,then the cost of changing the lineset.
    Seems to me the lineset can be easily changed (I can visually see the entire length of the lines to the exterior wall), but I don't know what is involved in changing a lineset. As far as cost, I think this will be a contractor expense since the house is 9 mos old and the new HP is being installed at no expense to me since the 3.5 ton unit turned out to be inadequately sized. I don't want an oversized unit, but I also don't want our cooling problems only partially corrected either.

    I have the original load calculation report, and another company has performed a new load calculation, and I have attempted a load calculation with the HVAC-Calc software available from this site. Suppose I obtain a reasonably valid load calculation and it came back one of the below values...what would you (or anyone else) recommend I do for each value???

    40,000 Btuh?
    42,000 Btuh?
    44,000 Btuh?
    46,000 Btuh?
    48,000 Btuh?

    As far as insulation, I haven't examined this and can only assume our brand new home is adequately insulated.

    Thanks,
    TLY

  8. #47
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    Aug 2002
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    Office and warehouse in both Crystal River & New Port Richey ,FL
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    Was a load calc used to determine it's undersized?

    Many new homes could ue more insulation,if that's possible they might rather pay for that then change the system and you'd be better served as well.

    Under warranty,their problem,change the lineset,exposed no big deal,if they change the system.

  9. #48
    Join Date
    Nov 2007
    Posts
    47
    Quote Originally Posted by dash View Post
    Was a load calc used to determine it's undersized?

    Many new homes could ue more insulation,if that's possible they might rather pay for that then change the system and you'd be better served as well.

    Under warranty,their problem,change the lineset,exposed no big deal,if they change the system.
    Yes, the new calculation came back needing a 4-ton unit. I haven't seen this report, but did ask if it was a Sensible + Latent calculation or a 75% Sensible load calculation. The new company said it was a Sensible + Latent calculation. I did ask for a copy of the report to see if the sensible load is being met because our sensible heat gain is quite a large percentage of our overall heat gain (large square footage and many, many windows).

    TLY

  10. #49
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    Quote Originally Posted by TLY View Post
    Yes, the new calculation came back needing a 4-ton unit. I haven't seen this report, but did ask if it was a Sensible + Latent calculation or a 75% Sensible load calculation. The new company said it was a Sensible + Latent calculation. I did ask for a copy of the report to see if the sensible load is being met because our sensible heat gain is quite a large percentage of our overall heat gain (large square footage and many, many windows).

    TLY
    Tinting the east and west glass helps reduce the load too.

  11. #50
    Join Date
    Nov 2007
    Posts
    47
    Quote Originally Posted by dash View Post
    Tinting the east and west glass helps reduce the load too.
    I have been considering a window film (3M-Prestige Series, PR 70) to help with our solar heat gain problems.

    TLY

  12. #51
    Join Date
    Nov 2007
    Posts
    47
    Quote Originally Posted by TLY View Post
    Suppose I obtain a reasonably valid load calculation and it came back one of the below values...what would you (or anyone else) recommend I do for each value???

    40,000 Btuh?
    42,000 Btuh?
    44,000 Btuh?
    46,000 Btuh?
    48,000 Btuh?
    I was hoping someone could give me an answer like "the first three values require a 4-ton unit and a 1-1/8in line, and the last two values require a 5-ton unit and a 1-1/8in line" or "all values require a 4-ton unit and a 1-1/8in line to satisfy the load requirement" or something along these lines to help me make some decisions.

    TLY

  13. #52
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Put in an R-410a system and it becomes a moot point, since the 7/8" vapor line will be the size specified for the unit.
    If more government is the answer, then it's a really stupid question.

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