Sunlit fraction of vertical slant windowpanes

When evaluating the instantaneous rate of solar heat gain through a window, it is essential to know the shaded area, if any, of the glazing. This is a typical standard drill, which is frequently carried out for conventional windows, which have the glass panes parallel to the building exterior wall. Sometimes, and for architectural or other reasons, the glass may be fixed in a vertical but horizontally rotated position; i.e. non-parallel to the wall. This may help to rationalize the energy requirements for air conditioning. The objective of this paper is to establish a systematic method to calculate the sunlit, and hence the shaded, fraction of slant-glass area. The presented analysis takes into account all of the numerous variables involved in the problem; namely, location, date, time of the day, wall orientation, rotation of glass relative to the wall, and geometrical characteristics of the window. The calculation procedure is casted in a general computer program which can be readily and unlimitedly used for any set of conditions. Some sample results are presented.