Sun on the Ground Analysis

[rorybergin]

We have noticed that forma does not account for cloud cover in its sunlight calculations, whereas EN 17037 and BRE Guides recommend metrics which account for cloud cover depending on location (London, Manchester or Edinburgh).

This means that our forma sunlight results for sun hours are counting almost 3x more sunlight hours than industry recommendations.

Is there a factor we can apply for the spring/autumn equinoxes and summer/winter solstices? Alternatively could the location or a climate file be applied to the sunlight analysis to provide more accurate results?

Sources:

https://help.autodeskforma.com/en/articles/6951253 -"Clouds/weather are not considered in the sunlight calculation"

"annual daylight hours per year: 4 ,380 hours"  - EN 17037 

"The APSH is the number of hours in a year that a window can be expected to receive direct sunlight, taking account of external obstructions and the likelihood of cloud cover throughout the year. In London, a south facing window unaffected by external obstructions can be expected to receive direct sunlight on its face for an average of 1,486 hours in a year". - RICS

https://www.rics.org/content/dam/ricsglobal/documents/standards/Daylighting-and-sunlighting.pdf

[maxime_briens]

Hello! Thank you for reaching out.

That is very interesting, thank you for taking the time to explain this. Sadly, as we are offering a solution available globally, we cannot always comply to the local regulations, and I believe that this is one of the cases where we allow you to get some insights, but they are not exactly matching what you need to assess compliance with your local regulatory needs.
First of all, I'm taking good note of your feature request and will prioritise it accordingly, as I believe that this is important for us to consider.

However, in the meantime, I would like to try to suggest a couple of ways that I believe could help you get closer to the insight you need:
- One way could be, similarly to what you suggested, to search for some weather data, and apply a coefficient of average cloud coverage, to mitigate the raw result of the sun hours analysis. I suggest you to take a look at the weather data from era5.
- A more streamlined way could be to use the microclimate analysis! You can read about it here. The main difference is that it takes the wind into consideration, but if you lower the speed of the wind, you simulate the microclimate without any wind. It does take into account the average cloud cover of the location at the given reference month, as well as other factors such as the humidity, direct and diffuse solar radiation, to estimate the perceived temperature, as measured by the UTCI. It will not give you results in terms of sun hours though.

I hope that you will find this answer helpful.

Maxime - Autodesk Forma