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  1. #14
    Join Date
    Jun 2005
    Location
    Near Chicago, IL
    Posts
    3,317
    Quote Originally Posted by Thebil Illpay View Post
    Thanks for the education. I plugged in 91%RH and 96 db [numbers that I understand] and came up with 240 grains of moisture. Plugged that into HVAC-calc and the numbers jumped. The system still works, but it will probably be running continuously in the second stage through most of the hottest months. I may go back, now that I understand this, and do a month by month assessment.
    I would think that the HVAC Calc program uses the same range and grains tables listed in the Manual J book as a basis for calculations.

    Moving outside of those values may create more problems than solving them.

    Having performed longhand residential load calcs and using HVAC Calc, there are differences in the data that can be input between the two methods.

    I suppose, if you are bored, a long form manual J and results from HVAC Calc could be compared.

  2. #15
    Quote Originally Posted by shophound View Post
    Manual J summer design conditions for N.O. is 92 degrees dry bulb/78 degrees wet bulb. That gives you a relative humidity % of 54, a dew point of 73, and grains of moisture per pound of dry air of 127.
    Well thanks for that information - even if you shouldn't have told me. I just selected the highest I found on published charts to see what would happen.
    The default setting for New Orleans on HVAC-calc is 100 grains. I'll go plug in 127 and see what happens. It's kind of fun.

    EDITid it. At 75 degrees indoor it changed the results to 22391 sensible and 4324 latent, total 26,715. At 70 degrees it brought both components up to 29 and change. That's only figuring two people.

  3. #16
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,317
    Quote Originally Posted by Thebil Illpay View Post
    Well thanks for that information - even if you shouldn't have told me. I just selected the highest I found on published charts to see what would happen.
    The default setting for New Orleans on HVAC-calc is 100 grains. I'll go plug in 127 and see what happens. It's kind of fun.

    EDITid it. At 75 degrees indoor it changed the results to 22391 sensible and 4324 latent, total 26,715. At 70 degrees it brought both components up to 29 and change. That's only figuring two people.
    I only told you so you'd have good information.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

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