It took some time to understand exactly how ASE is defined since many sources on the web are either interpreting ASE differently than LEED or do not understand LEED’s definition. In any case, I have checked this with others and I am confident that it is correct now. The example uses only Ladybug components and so it is able to perform the calculation pretty quickly. I know that @sarith and @mostapha also built ASE capabilities into Honeybee[+] and they’ll hopefully be putting up some examples on this soon.
Thanks chris! This is great, I’ll give it a look later.
I’ve been using HB+ for ASE with very good results lately but this should be faster (and a lot smaller in size) for those parametric models and/or large buildings.
From looking at the hydra script I’m still unclear on how the direct beam illuminance is being computed (ie taking away the diffuse component from direct normal illuminance). I would have thought you would have had to “subtract” in some way DirectNormal – DiffuseHorizontal in order to get just the sun effect and not the sky.
Also, everyone please note that on January 2017 the USGBC increased the ASE threshold from 10% to 20%:
Thank you for posting the credit interpretation from the USGBC. I wasn’t aware of the change but 20% ASE is so much more reasonable than 10%. I couldn’t even get a 20 WWR facade to pass the 10% criteria in some cases and I am glad that the USGBC has seen the light of reason I just updated the example to account for the USGBC’s interpretation: http://hydrashare.github.io/hydra/viewer?owner=chriswmackey&fork=hydra_2&id=Calculate_ASE_for_LEED
As for the calculation of direct solar illuminance for ASE, you are ultimately after the Direct Horizontal Illuminance (or, more specifically, the direct illuminance on a horizontal plane). You need this because the “desk” surface that a person is working on is likely horizontal and ASE only cares about the direct portion of the solar. However, this metric can be a bit of a pain to get because it is not included in EPW weather files and you have to calculate it, as you mention. Generally speaking there are two ways of getting this with Ladybug:
1) Subtract the Diffuse Horizontal Illuminance from the Global Horizontal Illuminance - This will leave you with the Direct Horizontal Illuminance. I imagine this is what you were suggesting in your post. Here is what this calculation looks like with Ladybug components:
2) Multiply the Direct Normal Illuminace by the Cosine of the Angle Between the Sun and Horizontal Surface - This is exactly what the “Ladybug_Surface Hourly Solar” component was designed to do. Specifically, the component is meant to quickly calculate the solar flux (or illuminance) on a surface facing any orientation from EPW solar values. It gives you both the values for the direct and diffuse components of the solar on the surface. So, as long as you ensure the surface of this component is horizontal (altitude = 90 degrees), you will get the Direct Horizontal Illuminance. This is how you use the component for ASE:
@alemenchaca I was reading the LEED v4 daylight requirements and guess that the ASE threshold has changed again since 2017 and it’s back to 10%!! which is a difficult number to achieve!
I just updated the example to account for the USGBC’s interpretation:
