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  1. #14
    Join Date
    Jun 2004
    Posts
    146
    Originally posted by jtalbert
    To Review: HVAC-CALC 4.0 gives me:
    Sensible Gain 20705
    Latent Gain: 1954
    Total Heat Gain: 22659
    Total Heat Loss: 38163
    Calc program Recommends a 2 ton system
    Heat pump to be installed for AC and heat

    Just talked to one of the HVAC contractors I have asked for bids and he said that the TVA here in Tennesee recommends to size system up to 125% of the sensible heat gain. That is to keep the heating element from coming on too early in the heating mode (aprox 35 dgrees) and degrading efficiancy.

    Does anyone know of this recommendation? I have not read anything on the forum regarding upsizing the system tonnage according to heat losses. I would appreciate any clarification on this issue. Thank you
    Question for all.

    A 2-ton AC or HP may have 24000 BTUH total cooling capacity. But the sensible cooling capacity is only about 18000 BTUH. So should the system be sized using total cooling capacity or sensible cooling capacity?

  2. #15
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,776
    Higher HSPF, units, usually have higher btu output at lower temps.

    Which in turn prolongs the strips from coming on.

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  3. #16
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,776
    Actually it should be sized to bothe, the sensible and the latent.

    Thats what manual S is for.

    The indoor and outdoor unit are to be matched to handle both loads.
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  4. #17
    Join Date
    Jun 2004
    Posts
    146
    Originally posted by beenthere
    Actually it should be sized to bothe, the sensible and the latent.

    Thats what manual S is for.

    The indoor and outdoor unit are to be matched to handle both loads.
    That would mean a 2-ton is too small for his sensible gain of 20705 especially since a lot of 2-ton's have sensible cooling capacity less than 17000.

  5. #18
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,776
    You'll find that you get some of the latent ability to become sensible after the humidity is down, it might not be enough for your house. And duct system.

    Your contractor will have to check teh spec sheets for the equipment he handles to select the correct match up, and yes 2 ton could fall short on sensible, depending what you keep your stat set to,

    that is also in the manual S.
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  6. #19
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,428
    [QUOTE]Originally posted by go_redskins
    [B]
    Originally posted by jtalbert
    A 2-ton AC or HP may have 24000 BTUH total cooling capacity. But the sensible cooling capacity is only about 18000 BTUH.

    So should the system be sized using total cooling capacity or sensible cooling capacity?
    Just be SENSIBLE about it everytime.
    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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