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  1. #1

    Question about tonnage needed with load calc

    Few questions for the pros out there.


    I have had a load calc done on my home: here are the specs below:

    1700 square foot 2 story house with finished basement in Titonka Iowa

    Heat loss@design------53,880 btu
    Temp difference-------81 degrees F (70 degree inside -11 outside)
    Degree days----------7,600
    Cooling load@design---26,736 btu
    Cooling load hours-----700


    electric rate is $0.048 September to April and $0.077 May-Aug


    Having this load calc done i am getting differences in system proposals.


    option 1:

    Mcquay 3 ton single stage heat pump with 10KW electric strip and ECM fan


    Contractor says he would use this and rely on some backup heat on the coldest days rather than oversize the system to avoid using strip heat, says its better.


    Option 2:

    Econar GeoSource Vara 2 Plus 4 ton 2 stage unit with 5 kw strip

    This contractor says that this is the way to go. says 4 tons and 2 stages with a 3rd electric strip stage is best. says this system fits right in with my load calcs i had done. (There is a 3 ton version of this unit too)



    Both units running in open loop. and both have desuperheaters



    I am not to sure what to do. The prices are not to much different from one another. Contractor 2 says that 2 stage cooling i will have better humidity control in summer. (i do not have a humidity problem now, and my current 4 or 5 ton single stage ac keeps it comfortable)

    Contractor 1 says that a 3 or 3.5 ton unit will have longer run times and keep up with humidity while making lots of hot water with the desuperheater and that in this part of the Midwest 2 stages are not needed as much as in the south. Though he did say that the Mcquay unit have an option for hot gas reheat for humidity control when hooked to a humidistat if i was concerned about it. (i am not)


    I have not found a lot of info on the Mcquay unit, they appear to be more industrial units.

    the Econar unit doesn't look to have really great efficiencies.


    Opinions on this?


    Thank you!


    Nate

  2. #2
    Join Date
    Mar 2011
    Location
    SOUTH DAKOTA
    Posts
    94
    Two stage without question much better performance and will be happier when air conditioning, and you don't need a relay to control electric heat just use the right t-stat

  3. #3
    Join Date
    Nov 2006
    Location
    TEXAS
    Posts
    806
    I'd look to go with the 2 stage. Unit should run in low most of the time in summer and keep the house comfortable, kick to high stage if needed. Also should run on geo during most of the winter. Strip heat is expensive to operate.
    Avatar is a tribute to my Great Grandfather, Andrew Stewart. This pin was one of his advertisements for his heating and plumbing business. I never knew him but must of inherited his love of things mechanical since I am the only blue collar worker in the family

  4. #4

    Two Stage

    Both would most likely work, but i would choose the two stage. I don't like relying on the strip heaters so much.

    But electricity is really expensive over here in Cali.

  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,040
    I certainly wouldn't go above a 3 ton with that cooling load. There's not much diff between low and high so even a grossly oversized 4 ton 2 stage wouldn't slow down that much. Could have humidity control issues in the summer. Also, I highly doubt a 1700 sq ft home has anywhere near a 4 ton duct system so things would get rather loud on high. Also you kill efficiency if you can't move the air the thing is designed to.

    McQuay is big in commercial, not residential. I'd look for a known name like WaterFurnace, Climatemaster or those they make like Heat Controller.

  6. #6
    Join Date
    Sep 2009
    Posts
    17
    I install all 2 stage units and this is the way to go. The 2 stage is for you loads. When you don't have a high load it will run on 1st stage. Thus reducing energy consumption and you get all other benefits. And if you run your fan continuously, you will have a more even temp in your entire house and it will not cost you hardly anything. And can I ask why you are doing an open loop and not a closed loop?

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