Window Solar Heat Gain and Conduction Cooling Load
The two ways a window adds to a cooling load: the solar radiation through the glass (area x SHGC x peak solar factor) and the conduction driven by the indoor-outdoor difference (area x U x CLTD). On a west wall in summer the solar term dwarfs the conduction by an order of magnitude, which is why orientation and SHGC, not U-value, drive a glass cooling load - the number to diagnose a hot room or justify a shading or low-SHGC retrofit. The peak solar factor is read from the ASHRAE/ACCA table for the orientation and latitude. One Manual J component, not the stamped load sheet.
Formula and source
q_solar = area_ft2 x shgc x psf; q_cond = area_ft2 x u_factor x cltd_f; q_total = q_solar + q_cond.
ASHRAE / ACCA Manual J fenestration cooling load (Q_solar = A x SHGC x PSF, Q_cond = A x U x CLTD), by name; the relations are public.
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