Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
Short Answer: If you had a space that was routinely occupied well into the evening, or conversely vacant for half the day, the metrics would potentially tell the wrong story, is all.
Longer Answer: The reason there are three values for each daylight metric (sDA excepted) is there is no prescribed temporal range for them. The OpenStudio Radiance measure just calculates for the three most interesting ranges, daylit, occupied, and "daylit and occupied". It's obviously pointless to calculate the daylight metric for nighttime hours, we know that is zero, right? But depending on the space type, it may be more useful to calculate the daylight metrics for when a space is known to be in use. We know the occupancy status from the occupancy schedule that is part of the OpenStudio model, and the daylit hours from the weather file, and the interior daylight illuminance from the Radiance simulation. From there we simply calculate the metrics, based on these three temporal input ranges. sDA has a specific range as dictated by IESNA (LM-83-12) for now, so that one we calculate accordingly -- just the one way.
The header in the report file attempts to explain the data within as well. Maybe it's unsuccessful. Sorry. Does this make sense now?
| | 2 | No.2 Revision |
Short Answer: If you had a space that was routinely occupied well into the evening, or conversely vacant for half the day, the metrics would potentially tell the wrong story, is all.
Longer Answer: The reason there are three values for each daylight metric (sDA excepted) is there is no prescribed temporal range for them. The OpenStudio Radiance measure just calculates for the three most interesting ranges, daylit, occupied, and "daylit and occupied". It's obviously pointless to calculate the daylight metric for nighttime hours, we know that is zero, right? But depending on the space type, it may be more useful to calculate the daylight metrics for when a space is known to be in use. We know the occupancy status from the occupancy schedule that is part of the OpenStudio model, and the daylit hours from the weather file, and the interior daylight illuminance from the Radiance simulation. From there we simply calculate the metrics, based on these three temporal input ranges. sDA has a specific range as dictated by IESNA (LM-83-12) for now, so that one we calculate accordingly -- just the one way.
The header As for the other elements in the report file attempts data:
metric_value - this is the metric. I don't know how to explain the data within as well. Maybe it's unsuccessful. Sorry. Does make this make sense now?
hours_met - number of hours where the metric criterion was satisfied. In your example, this would be the number of hours where the daylight illuminance was >= 500 lux (for DA and conDA) or >=100 <=3000 lux (for UDI).
input_hours - number of hours that met the criteria for consideration, i.e. were either daylit, occupied, or (daylit AND occupied), per column 'C' in the dataset.
