If the Time On and Time Off schedule for a window are set to 0:00 and 24:00 respectively (i.e. the Primary Material is used 100% of the time in the thermal calculations), the window’s Alt Material will influence Solar Heat Gains if its Alt Solar Gain (Lightwt) property is different from that of the window’s primary material. If I’m not mistaken, given this scenario, the Alt Material should not influence the Solar Heat Gain computation.

Likewise, if the Time On and Time Off schedule for a window are set to 0:00 and 0:00 respectively (i.e. the Alt Material is used 100% of the time in the thermal calculation), the window’s Pri Material will influence Solar Heat Gains if its Alt Solar Gain (Lightwt) property is different from that of the window’s alternate material. Given this scenario, I would not expect the primary material to influence the Solar Heat Gain computation.

The same problem occurs when mixing schedules. If the Alt Solar Gain (Lightwt) of Material 1 is different from that of Material 2, both materials will simultaneously influence the solar heat gain computation. If the values are equal, the Materials do not not influence one another (as expected) even if all other property values (e.g. U-Value, admitance, SHGC, etc...) are different .