An hourly lighting calculation model for the new Swiss Standard SIA 387/4

Abstract

A new hourly calculation method was developed and included in the new SIA 387/4, replacing the oversimplified one of SIA Technical Specification 2044. It connects to the calculation method of the standard for the installed lighting power and covers the same set of options for the control of the lighting system and of the solar protection as the revised existing factor-based annual calculation. The main improvements are the representation of the six control options for the daylight dependent lighting control, the options for its presence dependence, and the three options for the control of the solar protection. An hourly calculation of the visual transmittance of the window and solar protection combination was defined, based on European standards and the associated assumptions for the control strategies (blind slat angles). The method was implemented in a spreadsheet and checked against the factor based method. After some adjustments in both methods, the – not unexpected – differences between the methods appeared to be in the frame of +/- 20%, and the order of the results depending on the control options turned out to be correct.