Polished foils act as insulators when facing air. If they actually touch another material, the benefit is lost because heat flows by conduction instead of by radiation. The total thermal resistance of any construction is obtained by adding the thermal resistance of each of the component parts. Note however that when insulation is placed between framing memberss, the framing members present alternate heat paths of lower R value. A degree-day is day where the average temperature for that day is one different from 65 deg.
Infiltration amounts to a rate of heat loss.
An old wood frame building with windows rattling in the wind will totally change its air anywhere from two to ten times per hour depending on condition and exposure to wind. New construction of average workmanship will be about one exchange per hour. SC is the ratio of radiation through the window to a single glzed window exposed to sun from sunrise to sunset. 59 Y accounts for cloudiness.