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NC-v4.1 EQc7:Daylight

Sky type for Option 2: Illuminance

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Junaid Mujahid
Junior HVAC Design Engineer - Sustainability
PNC Architects
LEEDuser Basic Member
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If anyone has used IES-VE's RadianceIES application for Daylight Simulation Option 2: Illuminance, what sky type within RadianceIES should be selected for demonstrating compliance?

RadianceIES has these sky types and a few others:
1. Sunny sky

2. Standard clear sky

3. Standard CIE overcast sky

and others.

 

I'm confused whether to use the "Standard clear sky" or the "Standard CIE overcast sky" since the Standard clear sky is giving lower lux levels while the overcast one is giving higher lux levels and is "Standard CIE". Does LEED require only the use of "Standard CIE" sky types?

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Mon, 10/07/2024 - 14:13

For Option 2 Illuminance, the way I read the credit language is to use a clear sky from the TMY weather file, one that has the highest direct normal illuminance within the date parameters. That will have a Perez all-sky distribution given other factors in the weather file such as moisture in the air, which differs from CIE sky. I don't know IESVE, so I can't offer help in using that software to get it to display a Perez sky for a certain time. In the past I have identified this time by opening up the weather file in Excel and sorting etc to find the highest DNI within the date ranges at 9:00 and 3:00.  Credit language: Calculate illuminance intensity for sun (direct component) and sky (diffuse component) for clear-sky conditions as follows:
  • Use typical meteorological year data, or an equivalent, for the nearest available weather station.
  • 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.

Mon, 10/21/2024 - 18:53

Are you aware of any free software for simulation of Illuminance Calculations? I unfortuantely don't have Revit. Thank you,

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