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  1. #1
    Join Date
    Mar 2012
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    Cooling Load from- Solar Heat Gain

    Im using this standard formula for calculating soar heat gain BTU
    qsol = ASHGCI
    where : qsol solar gain [BTU/day]
    A- area in - [sf]
    SHGC solar heat gain coefficient
    I insolation, solar radiation incident on the glazing system surface [Btu/ft2/day]

    So in order to find solar gain for heating season and cooling season, Im averaging the insolation for heating months and cooling months, and multiplying it by the number of days in those respective months, and the result is in BTU.

    Now, when Im calculation annual energy losses , and dividing them by efficiencies of the equipment, I get confusing results :

    Energy Cost of Heating ($) = (q_(sol )∙182∙1/η∙C_ng)/(100 000)
    Energy Cost of Cooling ($) = (q_(sol )∙183∙1/COP∙C_ee)/(3 412.3)

    Cng price of natural gas $/therm
    COP coefficient of performance for the cooling unit
    Cee price of electrical energy $/kWh
    100 000 conversion from btu to therm btu/therm
    3 412.3 conversion from btu to kWh btu/kWh

    Because of COP > η (1/COP <1, and 1/η >1) I have solar gain in winter time higher that in summer , which doesnt make sense,

    And when Im calculating annual energy losses, I have to subtract winter heat gain from the energy of the rest of the year. When I do that, (because heat gain in winter is higher) the result is negative, which again doesnt make sense to me.

    How do you think I should do my calculation , where is my mistake, how I can handle this, taking in consideration that I need total annual losses ( per cooling and Heating seasons) in kWh and $.
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