Off the top of my head, and a brief look at the IDD, the windows don't have an obvious keyword to turn off incident radiation. There is an 'other side coefficients' field which you could utilize. However, I think the easiest way, since you aren't considering radiation anyway, is to just make a regular building surface using the same window material properties. For example, instead of entering your window glass as a window material, just give the same properties for a Material:Regular. I'm not 100% sure how the window gas will translate, but if you can come up with some equivalent properties, this would be the easiest way I could think of to model a window without radiation.