Continuous overcast daylight autonomy (DAo.con): a new dynamic metric for sensor less lighting smart controls

Abstract

Daylight dynamic metrics are useful tools for quantifying the switch-on time or the dimming of electric lighting according to the architectural scenario. A variant of these metrics can also be used to define strategies to control the lighting fixtures, dimming the luminous flux with no need for external input and reducing therefore the energy consumption of the lighting systems. Given this context, a new approach is proposed, Continuous Overcast Daylight Autonomy (DAo.con), defined as the percentage of occupied time when an illuminance threshold is met by daylight alone under continuous overcast sky conditions, considering a partial credit linearly to values below the threshold defined. This concept acts as an algorithm which adjusts the luminous flux of the luminaires according to the Daylight Factors measured or simulated, considering user requirements and ignoring any internal device for actively measuring the lighting conditions. The Daylight Factors can be modified according to the use of shading devices that affect to the indoor natural light. Accordingly, this algorithm can significantly reduce the embodied cost of the lighting smart controls, promoting their spread and its implementation in building refurbishment, while the energy consumption in electric lighting is reduced by up to 76% for large windows and by up to 65% for medium-sized openings. The results show that the use of this algorithm in office environments with LED fixtures can promote energy savings of up to 7.8 W/m2 for locations with predominantly clear skies and up to 5.7 W/m2 for northern latitudes with mainly overcast skies.