Hello!
I am interested to hear if anyone has done the ASE calc using the alternative "differences between adjacent grid points" methodology. The reference guide states: "For ASE analysis, direct sunlight can be assumed to occur for any grid point that has an hourly illumimance level at least 1,000 lux higher than any directly adjacent grid point. This could be determined from manual postprocessing of the simulation results, through a sun path and shadow program, or with software that automatically postprocesses the simulation results."
I'm unaware of a software that can postprocess data to determine this; technically, I think could do it manually in Excel - but would be a complete nightmare and given the amount of points I have, the Excel file size might become unmanageable.
I ran a sun-path simulation using Ladybug that determines the number of direct-sun hours for each point. In my opinion, this is a much more accurate analysis of direct-sun penetration than the 1,000 lux threshold that is used in the standard ASE calc. This has brought my ASE percentage down from 30% to 18% - which will allow my project to achieve 2 points under Option 1 - with the LEED interpretation 100002149 that allows projects with an ASE < 20% to comply as long as we submit a narrative that addresses how we designed to address glare. (I understand that if we have automated interior blinds, the ASE calc is exempt - but we are unsure at this time if our project will have this.)
I'm still not sure if my alternative ASE calc will be accepted by the reviewer. I am using a sun path and shadow program, but I am analyzing sun vectors and not differences between points. Has anyone else attempted anything similar to this?
Thanks in advance for any advice.
TODD REED
Energy Program SpecialistPA DMVA
LEEDuser Expert
889 thumbs up
March 13, 2018 - 1:59 pm
So here is some text from a discussion in a document from the IES Committee on daylighting about why the ASE of 1000 lux was set.
1000 lux was selected as the indicator threshold, because it was found to be a better indicator of the presence of sunlight for this purpose than a higher value such as 4000 lux, when compared to expert and occupant evaluations of the field study spaces. In direct field measurements, 1000 lux was also found to be a reasonable threshold difference between an observable ‘sunlight patch” and adjacent shadowed areas lighted by diffuse ambient daylight.
So, 1000 lux is set and establishes what is and is not direct sunlight. What is the set illuminance level in lady bug that determines what is and is not direct sun. If you know this, and show the reviewer that Lady bug is looking at each calc point and as long as that value is over 1000 lux, then i see no problem with the method you are using. Now you need to hope that the reviewer is knowledgeable in how this all works and that you make a clear and concise argument.
Adam Kyle
Associate PrincipalMEYERS+ Engineers
1 thumbs up
March 13, 2018 - 4:33 pm
Thanks for the reply. Ladybug is looking at the sun vector for each hour of the year (based on location) and the geometry of the space to determine whether a point is in direct sun or not; so it's not looking at illuminance at all. (So more like a shadow diagram.) The alternate ASE calculation says that we can use a "sun path or shadow program" - which is essentially what this is, but I'm still not sure if this methodology will be accepted because I'm analyzing whether a point is in direct sun - and not whether the point is 1,000 lux higher than adjacent points. (I'm specifically referring to the alternate ASE calc description in the reference guide - not the standard way you would calculate ASE).
TODD REED
Energy Program SpecialistPA DMVA
LEEDuser Expert
889 thumbs up
March 16, 2018 - 1:38 pm
I see what you are saying now. It took me a day to process this. Can you find out from the developer as to the properties of the ray(vector). There are rays that are the 100% true sunlight, then you have rays that are what we would consider "fuzzy". So if the develop has differentiation, and maybe some type of intensity, then you could use this as basis for the argument as to meeting the alternative compliance.
The other thought is this. As with any new version of LEED, things are tested and questioned because when it was written many years ago, there was just no way to know what would be out there to do this later on. Your not trying to game the system, its just what your program does. I say, run it, submit, if questioned, then it becomes a project LI, and maybe added into the ever growing LIs as more and more people attempt it.