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Thread: 4 ton vs 3 ton

  1. #1
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    4 ton vs 3 ton

    I’m relocating to SW Florida and currently soliciting bids for a replacement HVAC system. Two contractors said a 3 ton 2 speed system would provide ample cooling and de-humidification for my 1800 sq/ft home. Contractor number 3 who appeared to be very knowledgeable and helpful recommended the Trane 4TTX6048E (4 ton 2 speed unit). Although the 4 ton unit was oversized, this system would primarily be running at 2.5 Tons ( 7 amps) most of the time thus saving me considerable amount of money. He would add an additional return to accommodate the increase in cooling capacity.

    Q. Don’t all residential 2 speed scroll compressors perform this very same function with equal efficiency? If not:

    Q. What manufacturer incorporates the most energy efficient 2 speed scroll compressors in their equipment?

    Q. Will the increased price (significant) of this contractors recommended system prove cost effective?

    Appreciate the help,
    Mike

  2. #2
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    Every brand offering a 2-stage 16 SEER+ system is going to have the same unloading scroll compressor. Trane's Climatuff compressor is a bit different, but is more or less the same. The Trane is a nice unit, but I think you'll find that when looking at the actual performance specs, the unit runs more around a 3 ton capacity on low stage. So proper sizing is key. If you can use a 3 ton, and it's more appropriate for your ductwork system, then there is no reason to install a 4 ton. Because with these unloading scroll systems, low stage is not that much less than full capacity (roughly 75-80% capacity on low). If you do go with the 4 ton, then adding a return is a good thing, but having both adequate supply and return air is essential.

  3. #3
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    On first stage, the unloading compressor delivers 2/3 capacity or roughly 67% of 2nd stage. Choose your installing company carefully. There's a lot of hacks out there who just gues and guess again. Get the right company and you'll eliminate both the guesswork and your gambling thousands on one bet. Get the wrong company and you'll regret it for years to come in either discomfort, high utility bills or both. Happy shopping.
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  4. #4
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    Quote Originally Posted by skippedover View Post
    On first stage, the unloading compressor delivers 2/3 capacity or roughly 67% of 2nd stage. Choose your installing company carefully. There's a lot of hacks out there who just gues and guess again. Get the right company and you'll eliminate both the guesswork and your gambling thousands on one bet. Get the wrong company and you'll regret it for years to come in either discomfort, high utility bills or both. Happy shopping.
    That may be what the compressor is delivering in terms of capacity, but if you look at the spec sheets of Carrier/Bryant, for instance, the net capacity for each matchup is at least 80% capacity, in some cases more. Not to downplay the advantages of a 2 stage system.

  5. #5
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    Guy from Copeland said low was more like 75%. Read in a Nordyne technical manual that low was 80% "net refrigeration effect" whatever that is.

    I'm not sold yet on this technology, especially on the 16i. Some of the latent performance (humidity removal) numbers on it are rather poor. Do much better with a XR15 or XL15i single stage. Can't use dehumidify on demand with the 16i unless you have the communicating system either.

    Then there's the poor sap here trying to get his comps replaced on his dual compressor A-S/Trane unit. The big compressor on his 3 ton isn't available. Trane is expecting 17 in at the end of the month (truck from Mexico?) and have over 100 backorders for it. It's 95 and a sauna here, Florida weather.

  6. #6
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    Quote Originally Posted by MikeED View Post

    Q. Don’t all residential 2 speed scroll compressors perform this very same function with equal efficiency?

    When the unit run at low capacity (or first stage) it get more efficiency.

    Q. What manufacturer incorporates the most energy efficient 2 speed scroll compressors in their equipment?

    Lennox was the first to have this technology. Everyone else just follows. I don't know if they follow the same path or not.

    Q. Will the increased price (significant) of this contractors recommended system prove cost effective?

    This is hard to tell.
    But you need to know what you are after - Comfort or energy saving. You cannot have both at the same time.

    Appreciate the help,
    Mike
    Let me tell you the cons of 2 stages unit if NOT properly setup:

    Let say you set the temperature at 75 degrees cooling. Then your house temp creeps up to 76 degrees. The thermostat tells the A/C to run on low stage. NOW here comes the con - If the house and the A/C are at the balance point. Balance point means the heat gain within the house is THE SAME as the heat remove by your A/C unit.

    So at this stage the A/C runs and runs and runs for hours and hours and hours. The owner will make the phone call and says "My A/C runs all the time and will never shut off".

    If some how the cloud moves away and the sun beam on your roof, the temperature raise to 77 degrees. The thermostat tell the A/C unit to run the high stage. And it does because you hear the blower run faster and louder than last 3-4 hours.

    The cloud moves back and the house cool down to 76 degrees. The thermostat tell the A/C unit to run the low stage. And it does because you hear the blower run slower. ANd it stays like tht for another 2-3 hours before the sun completely out.

    So that is the biggest con that unknowledgeable A/C company will give you.

    So before you choose the system (Gods help don't choose trane), make sure that they provide you the thermostat that has the intelligence to get you out of this vicous cycle.

    Don't get me wrong. I love two stages system. Old days we call it two-speed system. I have one myself.

    Good luck.
    P.S. If my neighborh has a trane, I'll move.

  7. #7
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    4 ton 16i will be more like 3 to 3.4 tons in first/low stage.

    And seldom do you only need to add a return when you increase size by 1 ton. Usually need to add several supplies. And often modify the supply trunk, if you have one.
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  8. #8
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    Thumbs up 3 ton to handle Humidity ! !!

    Quote Originally Posted by MikeED View Post
    I’m relocating to SW Florida and currently soliciting bids for a replacement HVAC system. Two contractors said a 3 ton 2 speed system would provide ample cooling and de-humidification for my 1800 sq/ft home.

    Contractor number 3 who appeared to be very knowledgeable and helpful recommended the Trane 4TTX6048E (4 ton 2 speed unit). Although the 4 ton unit was oversized, this system would primarily be running at 2.5 Tons ( 7 amps) most of the time thus saving me considerable amount of money.


    Q. Will the increased price (significant) of this contractors recommended system prove cost effective?
    Mike
    The only reason to go to 4 tons is for SUMMER Party Time. The 4-ton would be real nice for parties > 20 people. However, I don't see it as a real value.

    Savings from Running A/C on 2-stage is not a primary concern. Comfort IS !
    Energy Savings is likely going to be in the $120 -$ 160 range per year for a 16 SEER. I would not term this amount as considerable.

    I will have considerable comfort when relative humidity is 40 - 44% !
    Designer Dan
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  9. #9
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    Quote Originally Posted by just_opinion View Post
    Let me tell you the cons of 2 stages unit if NOT properly setup:

    Let say you set the temperature at 75 degrees cooling. Then your house temp creeps up to 76 degrees. The thermostat tells the A/C to run on low stage. NOW here comes the con - If the house and the A/C are at the balance point. Balance point means the heat gain within the house is THE SAME as the heat remove by your A/C unit.

    So at this stage the A/C runs and runs and runs for hours and hours and hours. The owner will make the phone call and says "My A/C runs all the time and will never shut off".

    If some how the cloud moves away and the sun beam on your roof, the temperature raise to 77 degrees. The thermostat tell the A/C unit to run the high stage. And it does because you hear the blower run faster and louder than last 3-4 hours.

    The cloud moves back and the house cool down to 76 degrees. The thermostat tell the A/C unit to run the low stage. And it does because you hear the blower run slower. ANd it stays like tht for another 2-3 hours before the sun completely out.

    So that is the biggest con that unknowledgeable A/C company will give you.

    So before you choose the system (Gods help don't choose trane), make sure that they provide you the thermostat that has the intelligence to get you out of this vicous cycle.

    Don't get me wrong. I love two stages system. Old days we call it two-speed system. I have one myself.

    Good luck.
    P.S. If my neighborh has a trane, I'll move.
    I guess I'm missing something. How is that a vicious cycle? Seems like what you'd want it to do.

  10. #10
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    ^Ditto.
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  11. #11
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    Question

    Quote Originally Posted by just_opinion View Post
    Let me tell you the cons of 2 stages unit if NOT properly setup:

    Let say you set the temperature at 75 degrees cooling. Then your house temp creeps up to 76 degrees. The thermostat tells the A/C to run on low stage. NOW here comes the con - If the house and the A/C are at the balance point. Balance point means the heat gain within the house is THE SAME as the heat remove by your A/C unit.

    So at this stage the A/C runs and runs and runs for hours and hours and hours. The owner will make the phone call and says "My A/C runs all the time and will never shut off".

    If some how the cloud moves away and the sun beam on your roof, the temperature raise to 77 degrees. The thermostat tell the A/C unit to run the high stage. And it does because you hear the blower run faster and louder than last 3-4 hours.

    The cloud moves back and the house cool down to 76 degrees. The thermostat tell the A/C unit to run the low stage. And it does because you hear the blower run slower. ANd it stays like tht for another 2-3 hours before the sun completely out.

    So that is the biggest con that unknowledgeable A/C company will give you.

    So before you choose the system (Gods help don't choose trane), make sure that they provide you the thermostat that has the intelligence to get you out of this vicous cycle.

    Don't get me wrong. I love two stages system. Old days we call it two-speed system. I have one myself.

    Good luck.
    P.S. If my neighborh has a trane, I'll move.

    What your saying makes sense but let me ask a question so the picture is complete in my mind.

    Q. What type of thermostat eliminates the vicious cycles you are referring to? And wouldn't the contractor provide and install the type you are referencing?

    Thanks
    Mike

  12. #12
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    Aug 2010
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    Question

    Quote Originally Posted by RyanHughes View Post
    Every brand offering a 2-stage 16 SEER+ system is going to have the same unloading scroll compressor. Trane's Climatuff compressor is a bit different, but is more or less the same. The Trane is a nice unit, but I think you'll find that when looking at the actual performance specs, the unit runs more around a 3 ton capacity on low stage. So proper sizing is key. If you can use a 3 ton, and it's more appropriate for your ductwork system, then there is no reason to install a 4 ton. Because with these unloading scroll systems, low stage is not that much less than full capacity (roughly 75-80% capacity on low). If you do go with the 4 ton, then adding a return is a good thing, but having both adequate supply and return air is essential.
    Thanks Ryan for answering my question. Considering this particular Trane unit runs closer to 3T on low stage as you mentioned, it doesn't make sense to bump up my system to 4T. Q: Isn't there a residential 2 stage scroll compressor made with better operating ratios than 75-80/100?

  13. #13
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    Question

    Quote Originally Posted by dan sw fl View Post
    The only reason to go to 4 tons is for SUMMER Party Time. The 4-ton would be real nice for parties > 20 people. However, I don't see it as a real value.

    Savings from Running A/C on 2-stage is not a primary concern. Comfort IS !
    Energy Savings is likely going to be in the $120 -$ 160 range per year for a 16 SEER. I would not term this amount as considerable.

    I will have considerable comfort when relative humidity is 40 - 44% !
    Dan: Please explain why a two stage compressor is better at controling indoor humidity? Thanks for your help.
    Mike

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