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  1. #1
    Join Date
    Oct 2011
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    8

    2 stage unit other than 100%/66%

    I'm looking for a replacement 2.5 - 3 ton heat pump 2 stage unit. Problem is I only know about 3 ton units. A 2.5 ton two stage would be a good fit. If I need to use a 3 ton unit, I would prefer to find one that operates at a lower stage 1 "speed". Seems stage 1's most operate at ~ 66% of full power. Due to what needs to be done with zoning in this project, at unit that operates at stage 1 ~50% of full power would be a better fit.

    Can anyone recommend a unit that would do this? Or, know of a good 2.5 ton two stage unit?
    Carrier inverters won't work due to the zoning.

  2. #2
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    The compressor compression ratio is reduced to 66%, but the system operates more effciently because the coils and piping is now oversized, so power consumption is about 70-75% and capacity is about 75-80%.

    So turndown ratio is only 20-25%.

    Trane has their top of hte line XL20i that has 2 compressors that runs are 50% capacity.

    THe better option are the newer inverter based units comming out there. They slwo to abotu 25% speed and about 33% capacity. Currently there is the Carrier Greenspeed.

    For gas heating, modulating furnaces can drop to about 35% capacity. You can also use hydronics. With an outdoor reset you can go from 5-100% capacity based on water temprature. The boilers themselves can reduce ot about 10-25% capacity. But will cycle on and off if BTU requirements are lower. But youy have ot use a commerical air handler with a VFD to ramp down the airflow.

    Overall, sound like what you really want is a Carrier Greenspeed. Their 3 ton unit drops down to abotu 1 ton on low speed and can maintain nearly maximum heat output down to I think almost 15F. THe downside is that hte equipment I think is abotu a 50% price incrase from a Infinity 2 stage 17 SEER unit... which is already a 50% equiment price increase from a more basic 14 SEER 8 HSPF system.

  3. #3
    Join Date
    Feb 2006
    Location
    Float'N Vally, MS
    Posts
    1,873
    Quote Originally Posted by daveumbc View Post
    Carrier inverters won't work due to the zoning.
    I beleive Nordyne has a zone system that works with thier inverter model.
    I beleive you are mistaken about the greenspeed system.
    Life is too short, Behappy!
    TFMM

  4. #4
    Join Date
    Aug 2008
    Location
    Booneville, Mississippi, United States
    Posts
    263
    Check out the Maytag iq drive. Www.maytaghvac.com

  5. #5
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    5,520
    Quote Originally Posted by daveumbc View Post
    Carrier inverters won't work due to the zoning.
    Carrier Infinity Zoning is rpobably the best on their market and workse seamlessly with their Inverter units. Actually its' ideal since the dampers are also modulating. It can send precisely the CFM needed to each zone.

    Its 'a lot easier to find a Carreir dealer than a Maytag/Nordyne. THe Nordyne has been out there longer, but there are probaly already 10X more Greenspeed/Byrant Extreme's out there. Carrier/Bryant dealers that sell Greenspeeds must go through their special training.

    If my funding was unlimited, I'd have a Greenspeed hybrid zoned system in my downstairs. When I go to repalce it, I'll probably price it out, but will likely pick a mid range Performance series unit with a much better ROI and just use a basic zone system. IF your ductwork is oversized adequately, you don't need a bypass damper, and a low turndown ratio isn't much of an issue.

  6. #6
    Join Date
    Oct 2011
    Posts
    8
    Strange that the Carrier distributor tried to steer me away from Greenspeed and zoning. Maybe I miscommunicated...
    My duct work is adequate but undersized a bit. I guess anything will be a big improvement over the 17 year old Miller HP that is currently still working.


    Quote Originally Posted by motoguy128 View Post
    Carrier Infinity Zoning is rpobably the best on their market and workse seamlessly with their Inverter units. Actually its' ideal since the dampers are also modulating. It can send precisely the CFM needed to each zone.

    Its 'a lot easier to find a Carreir dealer than a Maytag/Nordyne. THe Nordyne has been out there longer, but there are probaly already 10X more Greenspeed/Byrant Extreme's out there. Carrier/Bryant dealers that sell Greenspeeds must go through their special training.

    If my funding was unlimited, I'd have a Greenspeed hybrid zoned system in my downstairs. When I go to repalce it, I'll probably price it out, but will likely pick a mid range Performance series unit with a much better ROI and just use a basic zone system. IF your ductwork is oversized adequately, you don't need a bypass damper, and a low turndown ratio isn't much of an issue.

  7. #7
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    5,520
    There were some early issues with the Infinity Zoning and the Greenspeed. I think it was mostly software and they have it ironed out now, but it might have hurt it's reputation.

    If you have a 2.5 ton now, a 3 tons 2 speed will still have longer run times and in cooling is most efficient in 1st stage anyway. IT probably will never use 2nd stage except in the hotest few hours of the day in the hotest day of the year, in the summer.

    FWIM I don't beleive setbacks in cooling save energy unless part of a time of use metering strategy.

  8. #8
    Join Date
    Aug 2008
    Location
    Booneville, Mississippi, United States
    Posts
    263
    Nordyne also requires special training, you can find many dealers under their umbrella of brands. Maytag, frigidaire, nutone , Westinghouse, tap pan, etc. all good. At least get an estimate for an iqdrive.





    Quote Originally Posted by motoguy128 View Post
    There were some early issues with the Infinity




    Zoning and the Greenspeed. I think it was mostly software and they have it ironed out now, but it might have hurt it's reputation.

    If you have a 2.5 ton now, a 3 tons 2 speed will still have longer run times and in cooling is most efficient in 1st stage anyway. IT probably will never use 2nd stage except in the hotest few hours of the day in the hotest day of the year, in the summer.

    FWIM I don't beleive setbacks in cooling save energy unless part of a time of use metering strategy.

  9. #9
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,768
    Trane 20i. first stage is 50%.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  10. #10
    Join Date
    Feb 2006
    Location
    Float'N Vally, MS
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    1,873
    Quote Originally Posted by daveumbc View Post
    My duct work is adequate but undersized a bit.
    Don't even consider this option if you are not willing to correct ductwork issues.
    This "MUST" work as a total system.
    Life is too short, Behappy!
    TFMM

  11. #11
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    5,520
    Quote Originally Posted by behappy View Post
    Don't even consider this option if you are not willing to correct ductwork issues.
    This "MUST" work as a total system.

    The ductwork is either adequate or it's undersized... not both. Going 2.5 to 3 tons is good sized jump in airflow. My other thought is whether a load calculaiton mgith supprot a 2 ton unit. A 2 stage 2 tons unit goes down to about 1.5 tons. Thats 50% of a 3 ton 2 stage without going to a high end inverter or 2 compressor unit and will dehumidify much better and have longer run times. You can undersize slightly if you use zoning if your zones manage yoru diversity from sun position and occupancy. Meaning in a non zone system, when it's sunny outside, part of hte home is usually getting overconditioned slightly and another under conditioned. Keep in mind too, that going form 2 tons to 2.5 tons means for example that if a 2.5 ton runs constantly at abotu 95F, the 2 ton unit will still keep up to about 92F before falling behind. Falling behind a little isn't a terrible thing. It's means your saving energy because return temp is higher, delta T heat gain is lower and run times are longer. Humidity is being controlled and should be very low from long run times, so a higher indoor temp will usually feel jsut as comfortable.

    Look at it this way... a 3 ton 2 stage might run almost constantly for a few hours but otherwise cycle on and off at night in 1st stage and never go to 2nd stage except setbacks or extremely hot weeather but will hold 73F indoors on a 95F day with lets say 50% RH. A 2 ton unit would run constantly in 1st or 2nd stage for many, many hours in the same conditions, and by early evening will lose maybe 2F and hold only 75F indoors. But indoor RH is 40%, so your actually more comfortable. The system catches up around midnight or 1AM.

    The difference? The 2 ton unit used maybe about 10% less energy from longer run times and lower airflow in the same size ductwork meaning it effectively gains 1-1.5 SEER. Something to consider.

  12. #12
    Join Date
    Aug 2010
    Location
    West Monroe, LA
    Posts
    1,537
    Quote Originally Posted by beenthere View Post
    Trane 20i. first stage is 50%.

    I agree with Beenthere Trane XL 20i might be the perfect unit for you? 50% rated capacity on 1st stage/smaller compressor. Then 100 percent capacity if the unit goes to 2nd stage/bigger compresser.

  13. #13
    Join Date
    Oct 2011
    Posts
    8
    This is a front/back system due to the back being an addition. The duct work in the front of the house (NNW side) is nicely oversized. My guess is it was sized for at least a 3 ton system, it has a 2.5 ton system.
    The back side is what I'm concerned about. It's an addition, 16'x33', a total of 3 floors if you count the basement/utillity room. 6 glass doors on the first floor. The man-j calls for 29K BTU's of heating and 23k of cooling. The ducts are a total if eight, 6 inch inner diameter flex duct, with three running to a 2nd floor. These are fed off a tee'd 20.5" X 9" internal insulated supply.
    I'd love to get a fourth to the 2nd floor but that would be somewhat major. We will be adding one more 6" line to the basement. The all this is fed by a 17 year old, highly rusted out, 2.5 ton horizontal unit. The outdoor unit is 2.5 tons, it is possible that the air handler is smaller and not matched. No one has been able to get any real info off the air handler. It's too rusted. This was a vented crawl space, before it was dug out, sealed, had a concrete floor poured, etc.



    Quote Originally Posted by motoguy128 View Post
    The ductwork is either adequate or it's undersized... not both. Going 2.5 to 3 tons is good sized jump in airflow. My other thought is whether a load calculaiton mgith supprot a 2 ton unit. A 2 stage 2 tons unit goes down to about 1.5 tons. Thats 50% of a 3 ton 2 stage without going to a high end inverter or 2 compressor unit and will dehumidify much better and have longer run times. You can undersize slightly if you use zoning if your zones manage yoru diversity from sun position and occupancy. Meaning in a non zone system, when it's sunny outside, part of hte home is usually getting overconditioned slightly and another under conditioned. Keep in mind too, that going form 2 tons to 2.5 tons means for example that if a 2.5 ton runs constantly at abotu 95F, the 2 ton unit will still keep up to about 92F before falling behind. Falling behind a little isn't a terrible thing. It's means your saving energy because return temp is higher, delta T heat gain is lower and run times are longer. Humidity is being controlled and should be very low from long run times, so a higher indoor temp will usually feel jsut as comfortable.

    Look at it this way... a 3 ton 2 stage might run almost constantly for a few hours but otherwise cycle on and off at night in 1st stage and never go to 2nd stage except setbacks or extremely hot weeather but will hold 73F indoors on a 95F day with lets say 50% RH. A 2 ton unit would run constantly in 1st or 2nd stage for many, many hours in the same conditions, and by early evening will lose maybe 2F and hold only 75F indoors. But indoor RH is 40%, so your actually more comfortable. The system catches up around midnight or 1AM.

    The difference? The 2 ton unit used maybe about 10% less energy from longer run times and lower airflow in the same size ductwork meaning it effectively gains 1-1.5 SEER. Something to consider.

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