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  1. #1
    Join Date
    Oct 2005
    Posts
    96
    Dan from SW FL was helping me size my heat pump and has went out of his way to help me with loads and sizing my system. In the morning I have to notify my contractor on what equipment to order which I plan to have installed in a week or so. I sent an e-mail to Dan this evening but unfortunately my mail server went down so I am forced to ask the question to the forum to see what you guys think so I have an answer in the morning.

    I believe Dan is having me oversize my heat pump based on my loads using a 2 stage compressorized system. The intent is to get as much electric heat out of the heat pump and plan to only run on the 1st stage of the cooling capacity based on the load calculations. For example if my first stage of cooling will give me up to 3.5 tons (which is my peak load) of cooling on a 5 ton unit that he is recommending that I install the 5 ton unit to gain the additional heating capacity. I'm in Kansas City so my weather is much different than Florida. Any thoughts.

    Dan, I appoligize if I mis-state anything that you have told me but like I said I'm at a loss for getting any e-mail due to my internet provider having my mail server down. If you happen to read this thread I want you to know that I am very grateful for all that you have done to assist me.

  2. #2
    Join Date
    Apr 2004
    Posts
    7,680
    If you size a heat pump for the heating load, you can pretty much count on having humidity control problems in cooling. ALWAYS size heat pumps for the cooling load. Now, if you have a 3.5 ton cooling load and new 2 stage stuff only comes in full tons, choose 4. Peak load is only a small portion of the actual required capacity.

  3. #3
    Join Date
    May 2004
    Location
    Rapid City, SD
    Posts
    7,415
    I could see rounding it up 1/2 a ton especially if it's multi stage system.

    But anything more than a 1/2 a ton is only going to hurt it in another area.

  4. #4
    Join Date
    Oct 2005
    Posts
    96
    If a VS fan motor is used wouldn't that also help to remove moisture on a two stage oversized system?

  5. #5
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,274

    Thumbs up R.H. Expectations

    Originally posted by docholiday
    If you size a heat pump for the heating load, you can pretty much count on having humidity control problems in cooling. ALWAYS size heat pumps for the cooling load. Now, if you have a 3.5 ton cooling load and new 2 stage stuff only comes in full tons, choose 4. Peak load is only a small portion of the actual required capacity.
    In general, run times at <81'F outside temperature would be quite low and possibly result in
    higher than optimum but satisfactory Relative Humidity levels.

    Given a properly charged 2-stage condensing unit
    and Variable Speed AHU adjusted to ~350 CFM per ton,
    one may expect ~48'F coil L.A.T. for
    Outside Air conditions of < 84'F.

    Run times are anticipated to be nearly or more than half the time at >_ 82'F outside temperature and would effectively provide ~50% Relative Humidity.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  6. #6
    Join Date
    Apr 2004
    Posts
    7,680
    I'll agree to disagree, its your story, you tell it.

  7. #7
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,274

    Thumbs up A/C and Tight Building Envelope

    MAINTAIN (attain)LOW INFILTRATION
    and
    Wet Bulb 11'F or more < Dry Bulb Temperature

    i.e. 75'F/63'F
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

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