The daylight coefficient method and complex fenestration

The daylight coefficient method has been introduced in computer simulation as an efficient approach to compute indoor daylight illuminances through building static fenestration systems. A set of coefficients are calculated only once prior to simulation start for a given number of elemental patches making up to sky vault and ground. However, for dynamic complex fenestration systems whose optical behavior (transmission, reflection and scattering) may change during simulation (such as windows with shadings), the efficiency of the daylight coefficient method may be compromised as the whole set of coefficients must be re-calculated during simulation. This paper presents the development of a new methodology to combine the daylight coefficient method with dynamic complex fenesration systems. The daylight coefficient is split into two components: one component corresponds to the unscattered transmitted light and the second to the scattered transmitted light. Both components are calculated based on the daylight coefficients of a reference fenestration, and the optical transmission characteristic and scattering effect of the actual fenestration. The resulting daylight coefficients for a given complex fenestration system may be calculated only once prior to simulation. This methodoly is implemented in Daylight 1-2-3, a new integrated energy and daylighting analysis tool for offices and classrooms. Initial validation studies, in which the results from the present method are compared with Radiance’s calculations, are carried out for a typical office space equiped with a clear window and interior Venetian blinds. The comparison shows that the new method is in good agreement with Radiance calculations, resulting in substantial simulation time savings.