Daylight performance predictions

Abstract

Daylighting describes the use of natural light in buildings. The objectives for daylighting a building are manifold and range from questions of aesthetics, occupant health and comfort to energy savings for lighting and space conditioning. Daylight simulations can help design teams to address these multiple aspects by allowing them to (a) predict the amount of light available inside or outside of buildings under selected sky conditions or over the course of a whole year and (b) to interpret the results by converting them into meaningful performance metrics. Daylight simulations can be combined with simulations of electric light sources in order to make sure that both forms of space lighting complement each other. They can also be embedded within an integrated lighting-thermal simulation in order to assess the overall effect of a daylighting strategy on energy use for lighting, heating and cooling (Janak 1997; Winkelmann and Selkowitz 1985). Within recent years it has become increasingly evident that the success of a daylighting strategy in real buildings is closely related to how exactly the electric lighting and shading systems are being controlled, e.g. manually, automatically or automatically with manual override. As a consequence, a new building performance simulation branch is emerging that specifically focuses on developing behavior models that mimic occupant use of personal controls in buildings such as light switches, venetian blinds, thermostats and operable windows (Newsham 1994; Reinhart 2004;ScopeThis chapter provides an overview of the different steps required to use daylight simulations for building design. Following an brief introduction to the theory of daylight simulations including common simulation algorithms, sky models and material descriptions, the debate turns towards the question of what to calculate, i.e. what daylighting performance metrics to use, how to address building occupant behavior and expectations and how to interpret simulation results in order to help design teams to make more informed design decisions. This chapter does not provide a general introduction into the larger theory of daylighting, e.g. how a lightshelf functions or how to commission a lighting control system.