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  1. #1
    Join Date
    Jun 2005
    SW Wisconsin

    Whole House Load Calculations - Fast & rather Easy

    Whole House Load Calculations - Why Not?

    Well, I thought it might help everyone to begin to do load calculations if I explained my experience with them.

    First, I did individual heat-loss & heat-gain calculations on spreadsheets, while accurate, that is slow & far more work than doing Free Internet load-calculations on a automated program. Being retired for a long time, I have been too cheap to buy a load-calculation program, because I probably would not use it much...

    While this Free Program only does whole house simultaneous heat-loss, heat-gain calculations, it is fast & easy to use for sizing the equipment, & showing what home retro-fitting can do to reduce the required Btuh..

    You can experiment with changing the design temperatures in both heat & cooling, (or start-over showing the New Retro-R-Values) also to see whether the equipment exceeds, at those particular temperatures & new retro conditions, (exceeds) the Btuh calculation load numbers, in each of the 3 cooling categories; Total Btuh, Sensible Btuh & Latent Btuh. Anyone can access Goodman Manufacturing - Expanded Cooling Data, & contractors can access the data of the equipment they handle.

    Some home owners will know the R-Values in the walls & ceiling, & the whole house square footage; the windows are rather easy, note the tree shading effects, etc. Therefore, the load calculations will not be time consuming, & anyone with good instructions & practice can do them.

    You can do the calculations as the house exists, & then do it showing the loads if more insulation, etc., were done to reduce equipment sizing, which makes everything related to the home & equipment much more efficient, thus optimizing the reduction of the home owner’s utility bills.

    On a home that has not been optimally weatherized, I’d use 0.7 ACH (Air Changes per Hour) be sure to add the (Air Changes per Hour) CFM into the ‘Fresh Air Recommended' line-slot, or it won’t figure the Infiltration Btuh.

    By all means start using the Free Load-Calculator
    Everyone; Get Cracken...

  2. #2
    Join Date
    Jun 2005
    SW Wisconsin
    Using Goodman Manufacturing or other Expanded Cooling Data; e.g., using a 2-Ton 13-SEER, R410A, @75F 50%RH Indoors; "outdoor 90F," ‘interpolate’ between 85F & 95F ambient, @800-CFM Mbh is 21.55, S/T is .765 * 21,550 is16,486-Btuh Sensible; 21,550 - 16,486 is 5,064 Latent.

    That simple math will get you close enough, so you'll know if the setup will handle the load using ACCA sizing methods. ACCA Manual S allows 115% of the load calc., IMO that's too much.

    Heat pumps in a cooling dominant climate are allowed to be 115% of the cooling level.

    Heat pumps in a heating dominant climate are allowed to be 125% of the cooling level.

    The size of the cooling equipment must be based on the same temperature and humidity conditions that were used to calculate the Manual J loads.

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