Abstract
Nowadays, daylight dynamic metrics are the most useful indicators to quantify the use of natural light, with daylight autonomy (DA) being one of the most widespread among all of them. This metric represents the percentage of the occupied time throughout the year in an indoor space when daylight reaches the minimum illuminance level to develop a specific task. Accordingly, the higher the percentage of DA, the shorter the switching on time of electric lighting. However, this metric considers for its calculations all business days of a whole standard year, and is thus not an accurate indicator for seasonal use spaces such as school classrooms. In this context, a variant of this metric is proposed, namely partial daylight autonomy (DAp), which is a non-lineal derivation of DA that considers those seasonal use spaces, helping to define the real percentage of indoor daylight use in order to properly quantify the accurate switching on time of electric lighting and therefore its energy consumption. As deduced from the analysis, the more precise results provided by DAp reach divergences close to 10% in comparison with the original conception of DA. Thus, this metric serves to estimate more accurately the impact on energy consumption if an electric lighting control system is implemented through lux meters. This new proposal has been monitored under real sky conditions in a test cell, providing converging results with those observed in the simulation process.
Highlights
Nowadays, building design pays special attention to the reduction of operational energy consumption
The real autonomy of daylight is lower than that determined by the classical metric of daylight autonomy (DA)
Where wfi represents the weighting factor that depends on the relationship between the illuminance threshold and the lighting value achieved by daylight, ti is the time fraction which corresponds to a certain illuminance value, according to a time interval throughout the year, ED is the daylight illuminance reached at the studied point and linked to a specific time fraction, and ET is the illuminance threshold defined for the task development
Summary
Nowadays, building design pays special attention to the reduction of operational energy consumption Given this context, electric lighting represents up to 30% of the total energy consumption in buildings, according to the climate and building function [1,2]. The most widespread concept in this context is the daylight factor (DF), which is the ratio of the illuminance level inside a given room to the illuminance level outside, determining the potential use of the natural source at a given indoor point under overcast sky conditions [12]. The indoor illuminance at a given point can be quantified knowing the outdoor illuminance This concept has served as a useful tool to determine the proper design of architectural features [14,15] to provide a suitable amount of natural light
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