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  1. #66
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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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    Not for the load.The exact equipment at conditions stated,is needed to decide which equipment size you need.

  2. #67
    Join Date
    Dec 2002
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    Houston,Tx.
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    Just in case you might not know, a heat load calc. is a great tool, but so is experience and common sense and what you just described is why.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

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  3. #68
    Join Date
    Feb 2007
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    Yes, 1-1/8" O.D. is the next size up from 7/8" O.D. I assume it's a 4 ton from the model number. Rheem/Ruud uses a capacity multiplier of .97, and calls it "optional". I seriously doubt if you'll have any performance problems, unless the old 4 ton didn't keep up in the summer. I assume you're replacing an R22 unit with another R22 unit, and that you're replacing the inside unit also.

  4. #69
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    Quote Originally Posted by TLY View Post
    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
    That's what I read,though they could be wrong,they were the first time around.What indoor temp> do you want in the summer?

  5. #70
    Join Date
    Nov 2007
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    47
    Quote Originally Posted by dash View Post
    That's what I read,though they could be wrong,they were the first time around.What indoor temp> do you want in the summer?
    72°. Why do you ask?

    Quote Originally Posted by dash View Post
    Yes,more tonnage increases air flow,and duct aren't often oversized to handle it.
    Hmm, this just puzzles me. My contractor said the same thing. Could you explain to me how by only changing the outside heat pump from a 3.5 ton to a 4 ton without changing any inside components will increase airflow. I'm not disbelieving this, I just don't understand how the airflow will increase.


    TLY

  6. #71
    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.
    Uh-hmm, did you read my previous post about my contractor and the lottery? I need to find some answers outside of my contractor.

    I wasn't so much looking for specific equipment recommendations, but rather some guidance along the lines of what the system tonnage needs to be in order to satisfy the range of Btuh's. But that's OK...

    As far as exact equipment...

    The plan is to keep the inside the same (Goodman coil, CAPF4860D6AA and Goodman furnace GMS91155DXAA) and change the heat pump from a 3.5 ton to a 4 ton (Goodman GSH130421AA to GSH130481AA).

    TLY

  7. #72
    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?
    This concerns me that the planned fix for my cooling problems is so rarely a proper solution. Do you have any recommendations for me?

    TLY

  8. #73
    Join Date
    Aug 2002
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    Office and warehouse in both Crystal River & New Port Richey ,FL
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    TLy,

    The load calc.(Man.J) will determine the btus of sensible and latnet needed for your home.

    Man. S will determine the correct equipment selection,from the detailed cooling capacity of the models(indoor and outdoor combo) within the brand of choice.

    Mfrs rating are
    generally at 80°F indoor for cooling,at lower indoor temps the capacity is reduced for the sensible portion of equipments capacity.

    You must derate the mfrs data as follows, 835 sensible btus for each degree below 80° indoors,for each 1000 cfms of air flow.

    Starting with a nominal 5 ton system,sensible =44,890 btus,and latent is 14,610,total 59,500 btus at 95° OD,80° ID,this is another brand just used for an example,so not the same as yours.

    Derate:
    835 X 8(degrees below mfr. specs) X 2( 2000 cfms,5 tons, divided by 1000 cfms)= 13,360 loss of sensible btus,from the 44,890 mfr rating at 80° indoor.So now only 31530 btus sensible and add the 13,360 to the 14,610 latent= 27970 latent.Half of any excess latent can be added back to the sensible,so some gain of sensible there.

    Outdoor design also effect the btus.

    If they did the load calc correctly,at 72°indoors,etc.,the derating of the equipment will likely mean you need a 5 Ton system,to get 72° ID,with 95° outdoors.If less then 95° ,more btus will be available.

    You have a 4 ton indoor unit,they can change the OD unit to 4 tons,and now the need 200 cfm more air flow from the same indoor unit(it was designed for up to 4 tons),they may or may not be able to get the extra cfms ,based on the duct system. 5 tons would need a different indoor unit and it's not likely they will get the required cfms ,with the same duct system. Low cfm also reduces sensible capacity,which can be determined,could even be part of the existing problem.


    There is a science to this and it all must be calculated to get it right .Rules of thumb,experience tells me ,etc.,etc.,are not a subsitute.

  9. #74
    Join Date
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    I don't think the air flow will change, but even if you stick with a 3.5 ton, the inside coil must be changed to match the ouside unit. If you don't, the best you can hope for is not enough heating and/or cooling. The worst that can happen, is that you'll burn out your compressor every 1 or 2 years. If your contractor says a 4 ton will work fine, then look for another contractor.

  10. #75
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    Feb 2007
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    You are definitely not going to be happy with a heat pump. If you want air conditioning, add it onto an oil furnace and use a Honeywell R7184U primary control or power venter made for oil.

  11. #76
    Join Date
    Nov 2007
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    47
    Quote Originally Posted by bobb25 View Post
    I don't think the air flow will change, but even if you stick with a 3.5 ton, the inside coil must be changed to match the ouside unit. If you don't, the best you can hope for is not enough heating and/or cooling. The worst that can happen, is that you'll burn out your compressor every 1 or 2 years. If your contractor says a 4 ton will work fine, then look for another contractor.
    I believe my indoor coil is rated for 4-5 ton capacity. Is it a 4 ton only? With my current setup, I was told it was common practice to have an indoor coil larger than the capacity of the outdoor unit (currently 3.5 ton).

    As far as looking for another contractor, our house is new (9mos) and our builder is trying to address our HVAC problems through the installing HVAC company. At this point, I do not have a lot of freedom to choose a HVAC company and can only allow my builder to correct our problems through whichever avenue he chooses.

    TLY

  12. #77
    Join Date
    Nov 2007
    Posts
    47
    Quote Originally Posted by bobb25 View Post
    You are definitely not going to be happy with a heat pump. If you want air conditioning, add it onto an oil furnace and use a Honeywell R7184U primary control or power venter made for oil.
    I'm not sure I'm ready to gut a brand new system at my expense. We are happy with the upstairs heat pump and it works just fine.

    TLY

  13. #78
    Join Date
    Nov 2007
    Posts
    47
    Quote Originally Posted by dash View Post
    TLy,

    The load calc.(Man.J) will determine the btus of sensible and latnet needed for your home.

    Man. S will determine the correct equipment selection,from the detailed cooling capacity of the models(indoor and outdoor combo) within the brand of choice.

    Mfrs rating are
    generally at 80°F indoor for cooling,at lower indoor temps the capacity is reduced for the sensible portion of equipments capacity.

    You must derate the mfrs data as follows, 835 sensible btus for each degree below 80° indoors,for each 1000 cfms of air flow.

    Starting with a nominal 5 ton system,sensible =44,890 btus,and latent is 14,610,total 59,500 btus at 95° OD,80° ID,this is another brand just used for an example,so not the same as yours.

    Derate:
    835 X 8(degrees below mfr. specs) X 2( 2000 cfms,5 tons, divided by 1000 cfms)= 13,360 loss of sensible btus,from the 44,890 mfr rating at 80° indoor.So now only 31530 btus sensible and add the 13,360 to the 14,610 latent= 27970 latent.Half of any excess latent can be added back to the sensible,so some gain of sensible there.

    Outdoor design also effect the btus.

    If they did the load calc correctly,at 72°indoors,etc.,the derating of the equipment will likely mean you need a 5 Ton system,to get 72° ID,with 95° outdoors.If less then 95° ,more btus will be available.

    You have a 4 ton indoor unit,they can change the OD unit to 4 tons,and now the need 200 cfm more air flow from the same indoor unit(it was designed for up to 4 tons),they may or may not be able to get the extra cfms ,based on the duct system. 5 tons would need a different indoor unit and it's not likely they will get the required cfms ,with the same duct system. Low cfm also reduces sensible capacity,which can be determined,could even be part of the existing problem.


    There is a science to this and it all must be calculated to get it right .Rules of thumb,experience tells me ,etc.,etc.,are not a subsitute.
    Oh, I only can wish that my contractor had such an approach. I'm afraid they are just going to swap it out and see what we get and I'm sure they will say that existing line will be just fine.

    TLY

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