% of Cloud cover

[FabianPosadas]

Hi Everyone,

I am doing a daylight study to comply with the “Collaborative for high performance schools” standard (CHPS). There are two paths for complying: Multiple point in time approach, and spatial daylight saturation approach.

I am trying to comply with the multiple point in time approach which is a method used to estimate annual average illumination. This method takes into account different points in time as well as percentage of opaque cloud cover.

I have worked on many daylighting projects for LEED and or optimization of visual comfort. But this one is my first for CHPS so I have never dealt with the % of cloud cover.

To try and get this % I started with the importEPW component

I took the values from the totalskycover output. I then used the “larger than” component to generate a list of true or false values to determine the hours when clouds where present. I summed up all those values to get total hours of cloud cover and divided by 8760 to arrive at that percentage. Now the thing that has me questioning is the way the values are outputed from the totalskycover output. The values come out in tenths so I am not sure if i should be counting cloud cover when its above a certain percentage of density. The pic above shows a true value anytime 1 tenth or more of clouds are in the sky.

Has anyone else here ever needed to calc % of cloud cover? is this the method you used?

Thanks in advance!

F

[devang]

Hi @FabianPosadas ,

In EPW, there’s data on opaque sky cover. I exposed that output for you in the attached file. Hope that helps.opaqueSkyCover.gh (377.9 KB)

[FabianPosadas]

Thank you @devang .

I see you are using 50% of the opaque cloud cover as the set point in your larger than input. That makes sense to me

“cloudy% percent of year with opaque cloud cover > 50%”

[mostapha]

@devang, should we add this output to the component now that there is an obvious use case for it?

[devang]

@mostapha I was going to ask you the same.