Results 1 to 11 of 11
  1. #1
    Join Date
    Oct 2007
    Location
    Northern Virginia
    Posts
    3

    Confused two stage vs. single stage compressor

    Hi everyone , There's lots of good info on this website and I've enjoyed sifting through it the past week. We are replacing my 15yr old 10SEER York heat pump and upgrading to a 16SEER unit for the upstairs zone -about 1500 sq ft (90% gas furnace and A/C still used for first floor and walkout basement). Will get a matching variable speed air handler and new t stat as well. Line set is 3/8 and 3/4 with 30ft of vertical and 27ft horizontal- no elbows just gentle curves. R-410A for the new HPand all 3 contractors know how to install it properly. We live in Northern Virginia so cooling has never been a huge issue but it would be nice to feel hot air from the vents in winter ( House is 15yr old with upgraded insulation and low-E glazing). The new 3ton contenders are: Carrier Infinty 16 , Trane XL16i , York 8t15 , or Rheem RPRL16. Will the new two stage compressors in a 16SEER HP handle the lift OK in the 67% mode or will they jump to 100% all the time? Do we need a TXV and/or solenoid to complete the installation? Will rated performance drop much? Will the wife finally get warm this winter??? Or should I settle for a 14SEER sinlge stage unit? Thanks for your ideas - Klifton

  2. #2
    Join Date
    Mar 2007
    Location
    Myrtle Beach, SC
    Posts
    2,919
    Why so big? 3 ton seems like a lot! The unit size will not determine the discharge temperature.

    I live in hot, humid Myrtle Beach, SC and my 2,000 sq ft house only has a 2-ton heat pump. A heat pump should be sized by the cooling load. It sounds like you need a competent contractor to do a proper Manual-J load calculation before you go any further.

    Please note that a 2 stage unit will not run any hotter than a single stage unit.

    A 2 stage is a good idea for different reasons, I have a 2-stage heat pump myself.
    Remember, Air Conditioning begins with AIR.

  3. #3
    When you say air handler are you talking about a new gas furnace or electric backup. That will make a difference.

  4. #4
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,929
    Yea, 1500 sq ft with good windows & insulation sure doesn't sound like 3 ton requirements. Bigger is NOT better. More cycling kills efficiency. Most 2 stage units on low have lower humidity removal rates so never going to high isn't good. To be efficient these new machines need to move plenty of air. Does your little house have a 3 ton duct system?

  5. #5
    Join Date
    Oct 2007
    Location
    Northern Virginia
    Posts
    3

    More info on two stage vs. single stage

    Sorry guys, being new, I wasn't very clear. 1500 sq ft is the size of the 2nd floor where this HP will be used- but I forgot to include 400 sq ft for the now finished extra room over the garage, it has two dormers. Also there is one skylight in an upstairs bath. So total may be closer to 2000 sq ft up there. The air handler for the 2nd floor is in the attic and has 15kw backup heat. 3 ton ducts? - maybe.. We have 12in. flex duct going to the garage room vents with separate return and 1in. fiberglass hard box with 8in.flex going to the other bedrooms with another return in the hallway. (My gas furnace with A/C is zoned for 1st floor and basement only-ducts in basement). A 3 ton HP is parked in the backyard now so a 3 ton replacement seemed reasonable. But I like your idea of getting the manual J done. My main concern was getting enough punch from the low stage of a two stage scroll compressor to overcome any lift issues. Do they deliver 2/3 the pressure / volume or 2/3 the tonnage on low stage? Thanks for your replies - Klifton

  6. #6
    You'd be fine with the two stage compressor. The reason I asked about the air handler as backup is that I suggest the Rheem system because for added comfort it has a watt restrictor that allows the backup heat strips to come on with the heat pump but limits the amount of power that they comsume and keeps outgoing air at 95 degrees. I have put in some of them and I really like the setup over bringing on backup as second stage only as you never have cold air just because your within the second stage seting on your thermostat. It may not be quite as energy eficient that way but if your not comfortable who cares about saving a few dollars.

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,770
    The 2 stage can handle the lift ok.

    Can't say about the others. But the York 8t has hot heat pump feature.
    It will slow down the blower so the air is warmer. Its a slight decrease in eff, but an increase in comfort.
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  8. #8
    Join Date
    Oct 2007
    Location
    Northern Virginia
    Posts
    3
    Thanks again for the help guys, -It's always better to Git R Done right the first time - less headaches for me and the contractor. Klifton

  9. #9
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    Quote Originally Posted by Kevin O'Neill View Post
    A heat pump should be sized by the cooling load.
    Not sure I agree with this statement. If the heat pump is used primarily in cooling mode, OK. If the climate requires heat during a large part of the year, and winters are rough, then a little oversizing should be OK. Especially on those frigid days where the heat pump needs as many btus as possible, and to minimize the back-up heat (electric resistance comes to mind).

  10. #10
    Join Date
    Mar 2007
    Location
    Myrtle Beach, SC
    Posts
    2,919
    Quote Originally Posted by gary_g View Post
    Not sure I agree with this statement. If the heat pump is used primarily in cooling mode, OK. If the climate requires heat during a large part of the year, and winters are rough, then a little oversizing should be OK. Especially on those frigid days where the heat pump needs as many btus as possible, and to minimize the back-up heat (electric resistance comes to mind).
    If you are in a heating dominant climate, AND summer dehumidification is not important, then sizing a heat pump by heating load is OK. Sometimes I forget that not everyone lives in my neck of the woods.

    But in areas where humidity is high in the cooling season, size by cooling load for the best dehumidification possible.
    Remember, Air Conditioning begins with AIR.

  11. #11
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,058
    Maximum virtical lift with the Trane is 25 feet virtical and 80 feet linear. The air handler would need to be variable speed and would have a txv.

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