For Option 2 (Simulation) is it accepted to run the simulation for 9.00 and 15.00 on September 21 only, or should it be repeated for March 21st and get the average of both? At page 730 of the Reference Guide it is stated that … “Perform one illuminance simulation at 9 A.M. on the equinox (September 21 or March 21). -•• Perform a second illuminance simulation at 3 P.M. on the equinox (September 21 or March 21)”, which means that the use only one of the spring or autumn equinox is needed. However, Figure 2 at page 733 refers to diffuse and direct horizontal radiation inputs for a sample weather file. How is this used with a local weather file which has been generated from specific meteorological data? Please note that we are using Ecotect with Radiance.
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Jill Perry, PE
ConsultantJill Perry, LLC
LEEDuser Expert
440 thumbs up
December 1, 2014 - 7:29 pm
I do not have the Reference Guide, but here is my understanding from the credit text.
You are supposed to create an imaginary day by averaging two sunny days, one *near* Mar. 21 and one *near* Sep. 21. These days cannot be further than 15 days from Mar. 21 and not further than 15 days from Sep. 21.
Meaning, analyze your weather file for the clearest day anywhere from Mar. 6th to Apr. 5th. Then pick the clearest day from Sep. 6th to Oct. 6th. Then if you know how to manipulate your weather file and enter a custom weather file into your simulation, average these two days and run the simulation for the one imaginary day.
OR, if you don't want to bother creating a custom day, run both the 9am and 3pm values for both selected days. Then, add up the illuminance values for 9 am and divide by two. Do the same for 3pm. Use these to determine your qualified area.
Here is the text from the credit:
- Select one day within 15 days of September 21 and one day within 15 days of March 21 that represent the clearest sky condition.
- Use the average of the hourly value for the two selected days.
The credit text also mentions the separation of the diffuse and direct radiation, but they don't talk about how to use it. I think they are trying to direct you on how to create the imaginary day in a weather file. However, since the overall magnitude of the radiation the reaches the calculation point varies directly with the overall magnitude of the radiation entering the space, I don't see how they could criticize the method of just averaging the lux numbers without altering the weather file.
Eddy Santosa
Director of SustainabilityDBR Engineering Consultants
376 thumbs up
December 2, 2014 - 1:58 pm
Regarding Ecotect and Radiance, you can probably use custom "gensky" command (-R and -B) in Radiance to input the radiation values based on your assessment.