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  1. #53
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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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    Quote Originally Posted by mark beiser View Post
    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.
    Nice idea,thinking outside the box.

  2. #54
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
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    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?
    The total btuh load isn't all that meaningful without knowing the sensible load.

    You could have a 42k total load, and still need a 5 ton system, or have a 46k total load, and need a 4 ton system.
    If more government is the answer, then it's a really stupid question.

  3. #55
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    Aug 2004
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    North Richland Hills, Texas
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    Quote Originally Posted by dash View Post
    Nice idea,thinking outside the box.
    There is no box.
    If more government is the answer, then it's a really stupid question.

  4. #56
    Join Date
    Nov 2000
    Location
    Eastern PA
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    Quote Originally Posted by dash View Post
    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.
    You just proved my point that we can play with the numbers in a variety of ways to justify what we want to propogate.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  5. #57
    Join Date
    Nov 2000
    Location
    Eastern PA
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    Quote Originally Posted by TLY View Post
    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
    The biggest red flag I am seeing is increasing the capacity of the system to fix a cooling problem. Ninety nine times out of a hundred, increasing the size of a system causes more problems then it could ever solve.

    Is your duct system going to be able to accomodate the additional air? Has dehumidification been discussed?
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  6. #58
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    Nov 2000
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    Eastern PA
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    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.
    Good advice. Again, I have not seen many applications where increasing the system capacity has been a good move. In reality, I have had much more success with dealing with heat gain and heat loss factors (such as dash is recommending) and "reducing" system capacity.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  7. #59
    Join Date
    Nov 2007
    Posts
    47
    Quote Originally Posted by mark beiser View Post
    The total btuh load isn't all that meaningful without knowing the sensible load.

    You could have a 42k total load, and still need a 5 ton system, or have a 46k total load, and need a 4 ton system.
    Good point...say the latent gain for each was 3500 Btuh.

    TLY

  8. #60
    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
    Good point...say the latent gain for each was 3500 Btuh.

    TLY
    Assuming that,you would need to look up the detailed capacity,at design conditions,indoor and outdoor,at the design cfms of the system per Man. J,for your exact equipment.

    As you see it's not a simple process,but the above should provide you the questions to ask your contractor.

  9. #61
    Join Date
    Nov 2007
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    47
    Quote Originally Posted by RoBoTeq View Post
    The biggest red flag I am seeing is increasing the capacity of the system to fix a cooling problem. Ninety nine times out of a hundred, increasing the size of a system causes more problems then it could ever solve.

    Is your duct system going to be able to accomodate the additional air? Has dehumidification been discussed?
    Nobody has said that it can't, but I really do not know. I just assumed the air would be colder...does changing from a 3.5 ton to a 4 ton increase the air flow?

    Currently, on a summer day the unit runs continuously and cannot keep up. The only discussion about dehumidification has been that too big of a unit will short cycle and not run long enough to adequately dehumidify.

    Currently, the indoor coil has a 4 to 5 ton capacity rating.

    TLY

  10. #62
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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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    Yes,more tonnage increases air flow,and duct aren't often oversized to handle it.

  11. #63
    Join Date
    Dec 2002
    Location
    Houston,Tx.
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    16,001
    Quote Originally Posted by TLY View Post
    Currently, on a summer day the unit runs continuously and cannot keep up.

    That could be a ton of possibilities, I had one last year or year before last I spent 3 days on and come to find out there was a "small" opening from the return air chase into the attic, large return you had to crawl back into the very back of it and in just one little corner of the return, was a place were a plumber pulled a pipe out and never plugged the opening or even mentioned it to anyone, I plugged up the opening and it made a difference like night and day.
    __________________________________________________ _______________________
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  12. #64
    Join Date
    Nov 2007
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    47
    Quote Originally Posted by dash View Post
    Assuming that,you would need to look up the detailed capacity,at design conditions,indoor and outdoor,at the design cfms of the system per Man. J,for your exact equipment.

    As you see it's not a simple process,but the above should provide you the questions to ask your contractor.
    I guess I am confused with need for the exact equipment to determine the load. For example, the HVAC-Calc program available from this site does not require specific equipment. The two other load reports have not specifiec specific equipment to determine the heat gain/loss.

    Should the exact equipment be listed on all reports? Confused...

    TLY

  13. #65
    Join Date
    Nov 2007
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    47
    Quote Originally Posted by Mr Bill View Post
    That could be a ton of possibilities, I had one last year or year before last I spent 3 days on and come to find out there was a "small" opening from the return air chase into the attic, large return you had to crawl back into the very back of it and in just one little corner of the return, was a place were a plumber pulled a pipe out and never plugged the opening or even mentioned it to anyone, I plugged up the opening and it made a difference like night and day.
    I'm trying to look at everything like that...the HVAC has been out many times looking and adjusting and they have determined the 3.5 was undersized. They are going to change it to a 4 ton at their expense.

    TLY

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