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  1. #14
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    Quote Originally Posted by craig1 View Post
    Its actually more complicated than that. When you reduce capacity, you reduce the work being done by the compressor, which in turn reduces its amp draw. So even if the restricted line causes a 3% capacity reduction, efficiency reduction might only be 1% or even nothing.
    under sized suction lines cause a capacity loss and hi velocity.....
    it was working.... played with it.... now its broke.... whats the going hourly rate for HVAC repair

  2. #15
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    Quote Originally Posted by craig1 View Post
    Its actually more complicated than that. When you reduce capacity, you reduce the work being done by the compressor, which in turn reduces its amp draw. So even if the restricted line causes a 3% capacity reduction, efficiency reduction might only be 1% or even nothing.
    I was just pointing out that you do in fact lose efficiency, not attempting to exactly quantify the efficiency loss.

    Continuing the discussion though, when you are dealing with total system capacity losses due to pressure losses, and other issues within the system, the electrical consumption per btuh of net refrigeration usually doesn't go down, or even stay the same.
    Typically it will go up.

    Either way, in most instances the small efficiency loss, due to the small capacity loss incurred by having the smallest recommended vapor line for the application, isn't worth the cost of replacing the refrigerant lines.
    If more government is the answer, then it's a really stupid question.

  3. #16
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    Quote Originally Posted by carmon View Post
    under sized suction lines cause a capacity loss and hi velocity.....
    Quote Originally Posted by mark beiser View Post
    I was just pointing out that you do in fact lose efficiency, not attempting to exactly quantify the efficiency loss.

    Continuing the discussion though, when you are dealing with total system capacity losses due to pressure losses, and other issues within the system, the electrical consumption per btuh of net refrigeration usually doesn't go down, or even stay the same.
    Typically it will go up.

    Either way, in most instances the small efficiency loss, due to the small capacity loss incurred by having the smallest recommended vapor line for the application, isn't worth the cost of replacing the refrigerant lines.
    Quote Originally Posted by craig1 View Post
    Its actually more complicated than that. When you reduce capacity, you reduce the work being done by the compressor, which in turn reduces its amp draw. So even if the restricted line causes a 3% capacity reduction, efficiency reduction might only be 1% or even nothing.
    Yes, it is more complicated than that. Remember pump laws and fan laws state that when you block flow, the amp draw is reduced. How much would be hard to determine and you may gain/lose efficiency or stay the same. Calculations for this stuff are just estimations, and you would really have to test it and get real numbers and plot an efficiency curve to find out. But with such a small difference, it doesn't really make sense to worry about. There are a lot of other things that can make a bigger difference, one being orientation and location of the condenser to minimize solar radiation effects which can raise the head pressure considerably and drop efficiency.
    Last edited by dijit; 02-16-2013 at 06:06 AM. Reason: grammar

  4. #17
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    Quote Originally Posted by dijit View Post
    Yes, it is more complicated than that. Remember pump laws and fan laws state that when you block flow, the amp draw is reduced. How much would be hard to determine and you may gain/lose efficiency or stay the same. Calculations for this stuff are just estimations, and you would really have to test it and get real numbers and plot an efficiency curve to find out. But with such a small difference, it doesn't really make sense to worry about. There are a lot of other things that can make a bigger difference, one being orientation and location of the condenser to minimize solar radiation effects which can raise the head pressure considerably and drop efficiency.
    Solar radiation doesn't have much effect either. unless the condenser is on a roof, or other surface that is reflecting both radiant heat and convection heat.
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  5. #18
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    Quote Originally Posted by 54regcab View Post
    If you really want to help lower power bills for the homeowner install a 2.5 ton instead of the 3 ton. If it can't keep up fix the leaks/solar gain in the house. Fudging the numbers on manual J calculations to get about 500sqft per ton that has been used since the 60's has got to stop. It's rare that a well designed house with a properly installed HVAC and duct system should need more than 750sft per ton.
    Its finally nice to see someone else thinking on the same page. I've been using for rough estimates around 700sft/ ton on sizing. It would be great if the "old guys" in the industry would pick up their socks, open their eyes and realize it's approx 40 years after their way was relevant. The worst is, most of the young apprentice's listen to them because they have been doing it for years. I had a guy tell me the other day that he was told by one of the head engineers at ******* furnace manufacturer, that static pressure was irrelevent. not to worry about it, that his ducts were fine. PARDON????

  6. #19
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    I have a 1.5 ton in an apartment with a 7/8 x 3/8 running 10 feet. The condenser is below grade of the coil. I hope my pressure drop is not severe.lol

  7. #20
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    So, How do 'you size an old house,built in '27 with NO 'upgrade's?
    My 'socks are just 'fine and,Yes,I do account for the Future.
    No matter how long you have been doing this,
    Go back and reread the Basic's.You WILL Learn something.
    Why is it called,an Act of GOD when IT has Nothing to do with Him?
    Will of the Devil would be more appropriate IMO.Just Saying.
    PSALMS, 18 & 25.
    I am a non college educated,white male and I made a difference.

  8. #21
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    My uncle'so new home has 10' ceilings, 3800 square feet. 2 car garage. 5 tons. House is very comfortable with low utility bills.

  9. Likes 54regcab liked this post
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