Ecotect Daylight factor

[sondakammoun]

Hi,

I'm using ecotect analysis 2010 and i'm asking if changing date affect the result of DF, it seems evident but i had the same result for the equinox and the solstice.

Thanks

[BaptisteDE]

Hi,

I might be wrong but Daylight Factor is not a fonction of sun position,

The DF is a % of accessible light inside a building under an overcast sky (wich represent the worst case scenario). It is not a dynamic analysis wich meen that it doesn't vary with the orientation or date and time.

[Boesselmann]

Hi,

quoted from http://www.archlighting.com/industry-news.asp?articleID=670541&sectionID=1306

Dayligth factor is a ratio that represents the amount of illumination indoors relative to outdoors at the same time. It typically is calculated by dividing a value of horizontal work plane illumination by the horizontal illumination available as measured horizontally on the roof of the building being tested.

From this follows that the date and time will have an influence on the results! A good option would be to set the simulation time to the 21st of March at noon with a intermediate sky. In this way you can get what probably is closest to the annual average.

best regards

Christian

[glennehill]

The issue may be tied to the Design Sky Illuminance you are using.  Generally DF is calculated with an CIE Overcast Sky.  An overcast ideal Overcast Sky has no Sunlight component, therefore the sky condition is calculated the same for all seasons.  The CIE Overcast Sky a 360deg Skydome with a gradient of 1:3 with the brightest part of the sky being the apex of the Skydome . The only value that changes is the maximum lux of the apex of the skydome. This is adjusted by the latitude of the site. I have not found a method in Ecotect to do Clear Sky analysis, which would have a Sunlight component and a non-uniform Skydome gradient.  Below is the Design Sky Illuminance comment Ecotect Light Analysis Wizard.  I hope this helps.

Design Sky values are derived from a statistical analysis of outdoor illuminance levels. They represent the horizontal illuminance that is exceeded 85% of the time between 9am and 5pm throughout the working year. Thus they offer a WORST-CASE scenario that you can design to and be sure you meet desired light levels at least  85% of the time.
The Design Sky you enter here is simply multiplied by the Daylight Factor at each calculation point to determine the actual daylight level.