Daylight illuminance set point / Set EP zone thresholds component results

I am trying to do window/wall ratio optimization with electrical energy use as fitness function. I want to take cooling, heating and lightning energy into account. For artificial light “sizing” I wanted to use workflow from this file. I started a thread about this here.
Browsing through components i found out that “setEPZoneThresholds” that I can set an illuminance set point for zones, as well as daylight control points. I set all my window/wall ratios to 25% (N,S,E,W) and although annual lightning energy use differs from core zone (no windows), the results for perimeter zones are suprisingly close to each other. For example the difference between norh and south zones is around 3%, and I would expect a much higher value.
Changing the window/wall ratio and adding some context defienately influences results, but these seem to be the only influential factors. Why is that so? Does Daysim take only only window size as a factor in this calculation?
Below i post image of energy use for lightning comparison and definition i used for the test. As I am a beginner it is highly possible i made a mistake somewhere. I kindly ask you to review it if possible.

test openstudio (642.5 KB)
Thank you for your time and help!

Hi @Wujo,

EnergyPlus component won’t affect the Daysim results. If you want to set the location of the sensor for Daysim you should use Lighting control recipe component otherwise all the test points will be considered as sensors.

Thank you for your reply. I know how to set things up with daysim components thanks to your example file i mentioned earlier. Still I am curious how things work with EP Thresholds component
There is “illuminance set point” and there are “daylight control points” as imputs. Descriptions indicate that the first one is value beyond which lights will be dimmed, second is location of “sensor points” If it is impossible to run daysim simulation through HB with openstudio or energyplus, how are these values calculated? Why are these the same for all directions, and how come lightning energy use is changed when I add context (when it doesn’t affect daysim)?

@Wujo ,

Sorry for the late reply. @mostapha is right to point out this this workflow is not using DAYSIM at all but rather uses EnergyPlus/OpenStudio’s built in methods for estimating illuminance at a sensor point (and modulating the lights accordingly). This is often faster than the annual calculation with DAYSIM but it’s not as accurate (it’s usually still good enough to give you a decent estimate of your lighting energy savings with daylight control).

The results make sense to me in that the lights are being dimmed any time that there is daylight falling on the sensor point (in order to meet the illuminance setpoint 500 lux). Because your perimeter zones are not that deep, this is basically for the entire daytime. You can see in the label zones component that the sensors are only 3 meters from the facade:

. Given that your window head height is also ~3 meters, I would expect the diffuse light of the sky to be enough to trigger the dimming.


Hello Chris,
You mentioned diffused light of the sky. Does that mean that EP uses diffused sky model for each day of the year (unlike daysims climate-based for annual analysis)?
Sorry for asking such specific questions, I would like to understand better where the big differences between results come from. If you know a resource where i could find out more on how EP handles daylight, please send it to me if possible.

Check this link for an answer to your questions…