DAYSIM Header File Keyword: Daylight Autonomy

The daylight autonomy at a point of interest  in a building is defined as the fraction of the occupied times per year, when the required minimum illuminance level at the point can be maintained by daylight alone. In contrast to the more commonly used daylight factor, the daylight autonomy considers all sky conditions throughout the year. It can nowadays be reliably simulated using dynamic daylight simulation methods.

Note: The daylight autonomy depends on the illuminance requirements of the user, occupancy hours, and the status of the blinds throughout the year. The latter is characterized in the Lightswitch Wizard through the blind control as well as the user behavior. On the other hand, the daylight autonomy is independent of the installed electric lighting power and lighting control. A high daylight autonomy is therefore a necessary requirement but not a guarantee for lighting energy savings due to daylight.

Example
A daylight autonomy of 70% for a work place with working hours on weekdays between 7 a.m. and 6 p.m. and a minimum illuminance levels of  500 lux informs that the occupant can potentially work 70% of the year by daylight alone.

 


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