VSC with SkyView, ViewPercent or Legacy VSC?

grasshopper honeybee
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Sky View, View Percent or Legacy VSC for vertical sky component calculation?

I’m trying to calculate the vertical sky component of a façade, and comparing different methods available in LB/HB 1.4.0 and HB Legacy.

As I’ve understood it the SkyView component of HB 1.4.0 is similar to the old verticalSkyComponent component of HB Legacy when run on vertical surfaces with a cloudy sky model. See Ladybug Tools for Grasshopper 1.3.0 Release

I’ve also tried the ViewPercent component of LB 1.4.0 with the “view type” set to “Sky Exposure”, which yields similar results.

Both components however give somewhat higher values than I’d expect, and approximately a factor two higher than the verticalSkyComponent component of HB Legacy.

My questions are:

Can both SkyView and ViewPercent be used for VSC calculation?

What could explain the discrepancy between SkyView/ViewPercent 1.4.0 and verticalSkyComponent Legacy?

Have I misunderstood any of the components and how they’re supposed to be used?

You can find the script here if you’d like to take a look. Thanks for the help!

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The best way to do this is with the HB Sky View component but you need to read the description carefully:

Note that computing cloudy Sky View for a vertically-oriented geometry (horizontal sensor direction) will yield Vertical Sky Component (VSC) as described by the UK Building Research Establishment (BRE). VSC is defined as the ratio of cloudy sky illuminance falling on a vertical wall to the simultaneous horizontal illuminance under an unobstructed sky [Littlefair, 1991].

So you must use the cloudy_sky_ option in order to get VSC as it’s defined by the BRE.

The Ladybug View Percent component cannot be run with a cloudy sky and so you cannot get VSC from it. However, the LBT Honeybee “Sky View” component with the cloudy option is effectively equivalent to the Legacy VSC recipe. So the Legacy workflow is also valid, though it is old and deprecated.

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Dear all,
Do you know studies/guidelines setting minimum Skyview factor to respect for solar urban planning?
Kind regards,
Romain