I have some questions about the daysim simulation report, please help.
What does the text marked in red actually mean?
Daylight Autonomy (DA) Analysis: The mean daylight autonomy is 78% for active occupant behavior. "The percentage of the space with a daylight autonomy larger than 50% is 79% for active occupant behavior." 1
Useful Daylight Illuminance (UDI): The percentage of the space with a UDI<100-2000lux larger than 50% 2 is 100% for active occupant behavior.
In climate based metrics DA, CDA, UDI, daylight availability the sensor receives the threshold illuminance for 100% of time for the active occupant behavior or only 50% or more of it? I want to understand the relationship between the threshold illuminance and the active occupant behavior. 3
For climate based metrics, DIVA measures the illuminance at each analysis node in your scene during all 8760 hours in a year. "Active occupant behavior" refers to the subset of those hours during which people are present. (Say, Mon-Fri, 8:00-18:00 for a typical office.) Let's simply refer to these as "occupied hours" below. Each metric (DA, UDI, etc.) is assessed for each node independently, and then DIVA lists some statistics about all the nodes taken together. With that in mind:
1) Daylight autonomy (DA) is the percentage of occupied hours during which a node experiences greater than the threshold illuminance (say, 300 lux). Mean DA (78%) is what you get when you take the average of the DA values of the nodes in your scene. The second sentence (red) conveys that 79% of your nodes have a DA greater than 50. (Why 50? Well, it's somewhat arbitrary, but we might like to say a node is 'daylit' if it experiences adequate illuminance more than half the time.)
2) For UDI, the story is the same, but the threshold(s) have changes. In this case, every node in your scene (100%) has a UDI greater than 50. I.e., for every node in your scene, it is true that the node experiences between 100 and 2000 lux for more than half of occupied hours.
3) To summarize, a climate based metric provides a statistical description of an individual node over all the hours during which occupants are present. For DA, it's how often the illuminance at the node is above a threshold. For UDI, it's how often the illuminance is between two thresholds. If a node receives more than 300 lux for 75% of occupied hours, and less than 300 lux for the remaining 25% of occupied hours, then the node's DA(300) value is 75. If you have two nodes with DA values of 75 and 55, then mean DA will be 65, and the "percentage of the space with a daylight autonomy larger than 50%" will be 100%, since both nodes have values greater than 50.
Hope that helps,
Hi Shwas -- see my comment here.
Is it possible to change the daylight autonomy larger than 50% to another value?
The new Green Star tool in Australia requires DA160[80%] - i.e. Daylight illuminance of 160Lux for over 80% of the time for a specified area.
Hope you can help,
In DIVA-3, using the Grasshopper components, it is easy to filter for values greater than 80%. Using the toolbar, you could open the results in Excel and simply count the number of sensors with a DA value larger than 80 and compare that to the total number of sensors.
In our forthcoming DIVA-4 (to be released as beta soon...), you can type in the range over which to display DA values in when loading your results, and statistics are generated in the Rhino viewport. So look out for that.
Great. Thanks for your help Alstan.