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  1. #1

    New Geothermal System - 2-stage or single?

    I'm replacing my 30-year old Geothermal system with a new one. I have four quotes, all of them telling me the house duct-work, etc. was designed well and efficient. One issue is the house is over 4,000 sq ft and the current system has only one zone, which will be fixed to two zones with the new system.
    Three of the HVAC guys tell me I should do a 2 stage system - save energy, etc. The fourth is suggesting a single stage for a few reasons: He has replaced a lot more compressors on two stage units than single stage units (even saying his mfg rep says the same thing), the zones will still have over 2,000 sq ft each, the house is brown, open to sun with a lot of windows, etc. so the system will still need to crank 100% most of the time when it's on anyway. It's also less expensive - though not by much so that's not an issue. My issue is that the guy suggesting the single stage has been helping with my current system for years - I trust him, etc. He says he's taken everything about my house into account and would suggest the single stage. That said, he's OK to install the two-stage if that's what I want.
    Thoughts from anyone in the business?
    Thanks,

  2. #2
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,698
    I would recommend the 2-stage with or without the zoning. It'll give you better comfort and dehumidification.

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,095
    2 stage.
    Contractor locator map

    How-to-apply-for-Professional

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

  4. #4
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,665
    2 stage with the copeland 2 stage unlading scroll compressor this compressor has proved to be very reliable and efficient

  5. #5
    Join Date
    Feb 2010
    Location
    In a boiler room
    Posts
    7,124
    2 stage compressors do not have a higher fail rate in my experience. Unless we are talking about the Bristol TS.

    If he has a large number of compressor failures, I would question his design and installation practices. Any compressor can be killed if it is starved for airflow or any number of other installation shortcuts.

  6. #6
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    2-stage is standard for our company. That said, if you become sold on the 1-stage, then I'd highly recommend a whole house dehumidifier be installed concurrent with the new geo unit. That'll go a long, long way toward controlling humidity. Something a 1-stage system is not noted to do as well as a 2-stage, particularly if you're in a heating dominant location.

  7. #7
    Join Date
    Feb 2010
    Location
    In a boiler room
    Posts
    7,124
    Quote Originally Posted by skippedover View Post
    2-stage is standard for our company. That said, if you become sold on the 1-stage, then I'd highly recommend a whole house dehumidifier be installed concurrent with the new geo unit. That'll go a long, long way toward controlling humidity. Something a 1-stage system is not noted to do as well as a 2-stage, particularly if you're in a heating dominant location.
    Good point.

    I forgot to mention, if in a predominately heating climate size lo stage for cooling load (given proper ductwork sizing). That way you have more capacity for heating.

  8. #8
    Join Date
    Jan 2002
    Location
    East Grand Forks, MN
    Posts
    1,373

    It's the only way to design a Job!

    Can't answer this question until I see your Load Calc.
    If you want professional advise then I need to see the Load-Calc!

  9. #9
    Join Date
    Feb 2009
    Location
    Portland OR
    Posts
    1,991
    Two stage is also usually more efficient. When your operating in low stage it's like driving a Prius to heat or cool the house. Jump into high stage and your driving a truck. I can't think of a reason to go single stage. I won't even install a single stage geo.

  10. #10
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by SkyHeating View Post
    Two stage is also usually more efficient. When your operating in low stage it's like driving a Prius to heat or cool the house. Jump into high stage and your driving a truck. I can't think of a reason to go single stage. I won't even install a single stage geo.
    Isn't that anaology a little extreme? I rembmer reading that in heating, the Trane XL16i according to it's data sheets showed very little diffrence in heating efficiency in high vs. low stage. Of course a water source unit may be different. I would think it's more like comparing a Prius to a Toyota Corolla in term of effieciency.

  11. #11

    Geo single vs two stage

    Thanks to all for the replies. I'm still thinking about it, but leaning to the two stage because of the dehumidification issue (I live in Massachusetts) plus the long warranty on the compressors.
    FYI - Three of the guys quoting did the heat/load calculation and agreed the 6-ton geo system is good for my house. That's what's here currently and it's served us well, especially given it's 30 years old. They also calculated the return air and it's good as well.

  12. #12
    Join Date
    Jan 2008
    Location
    s chester county,pa
    Posts
    144
    2 stage with desuperheater and extra domestic storage tank

  13. #13
    Join Date
    Apr 2010
    Location
    Minnesota
    Posts
    517
    I vote for 2 stage.

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