[Radiance-general] Current practice for LEED sky modelling?

Tue Jun 19 09:28:16 PDT 2012

Hi, just add to Robert's comments:

The journal paper based on the IES paper as mentioned by Robert:
Ward, G., Mistrick, R., Lee, E. S., McNeil, A., & Jonsson, J. (2011).
Simulating the Daylight Performance of Complex Fenestration Systems Using
Bidirectional Scattering Distribution Functions within Radiance. Journal of
the Illuminating Engineering Society of North America (Leukos), 7(4).

Another paper by Andy on related topic:
McNeil, A. (2011). The Three-Phase Method for Simulating Complex
Fenestration with Radiance, from
http://radiance-online.lbl.gov:82/learning/tutorials/three-phase-method-tutorial

- Cheers, Ji

On Wed, Jun 20, 2012 at 12:02 AM, Guglielmetti, Robert <
Robert.Guglielmetti at nrel.gov> wrote:

> Yeah, the sun luminance and solar disc size is based on Greg's
> implementation of the CIE standard sky model in gensky. The Perez sky
> model has been shown to have problems with low sun angles but does a nice
> job otherwise, when given weather info (e.g. TMY, EPW).
>
> The problem of course comes when you want to use these sky models in a
> daylight coefficient approach, where the sun's luminance is spread around
> the three nearest patches to the actual solar location. The Tregenza
> subdivisions are way too big to make for accurate estimations. This is why
> Reinhart and Bourgeois proposed the finer resolutions you get when you use
> the -M:2 or -M:4 options in rtcontrib. -M:4 gives you over 2000 sky
> patches instead of the original 145 proposed by Tregenza. Greg, Andy, Rick
> Mistrick and Eleanor Lee covered this nicely in a paper a couple years ago
> at the IES conference.
>
>
> Rob Guglielmetti  IESNA, LEED AP
> Commercial Buildings Research Group
> National Renewable Energy Laboratory
> 15013 Denver West Parkway MS:RSF202
> Golden, CO 80401
> 303.275.4319
> robert.guglielmetti at nrel.gov
>
>
>
>
>
> On 6/19/12 9:41 AM, "Lars O. Grobe" <grobe at gmx.net> wrote:
>
> >Hi Chris, Rob, so what are you using as sun luminance? Some average from
> >weather data? A theoretical value from a model? John's examples are a
> >great demonstration for the problem. I am rather sure that an invalid
> >assumption for the direct sun in a sky model would by far outnumber the
> >effect of changing a sky distribution to whatever model. Is there common
> >sense that if "clear sky" is referenced, I should use the CIE clear sky
> >without any modification, just as what I get from gensky? Or should I
> >feed in at least an illuminance reading either from my own measurement or
> >from weather data?
> >
> >Cheers, Lars.
> >--
> >Dipl.-Ing. Architect Lars O. Grobe
> >
> >On Jun 19, 2012, at 17:59, "Guglielmetti, Robert"
> ><Robert.Guglielmetti at nrel.gov> wrote:
> >
> >> Yeah, the LEED "clear sky" absolutely means a clear sky with a sun
> >>(unless
> >> they've changed it recently in LEED). ALL of my clear sky simulations
> >>with
> >> Lightscape, AGi32, and Radiance over the years have included the sun.
> >> After all, aren't we trying to predict daylight performance??
> >>
> >> Hey Chris, when'd you move to New York? Congrats, and enjoy the
> >>humidity.
> >> =8-)
> >>
> >>
> >> Rob Guglielmetti  IESNA, LEED AP
> >> Commercial Buildings Research Group
> >> National Renewable Energy Laboratory
> >> 15013 Denver West Parkway MS:RSF202
> >> Golden, CO 80401
> >> 303.275.4319
> >> robert.guglielmetti at nrel.gov
> >>
> >>
> >>
> >>
> >>
> >> On 6/19/12 7:16 AM, "Chris Coulter" <Chris.Coulter at burohappold.com>
> >>wrote:
> >>
> >>> Lars,
> >>>
> >>> I have done several LEED compliance calculations in the past using
> >>>clear
> >>> sky with sun (+s as the gensky parameter). This allows for daylight
> >>> redirecting devices to push light further into a space, and more
> >>> recently the requirement for glare control above 500fc.
> >>>
> >>> My take is that the phrase "clear sky" does not mean "clear sky without
> >>> sun" as might be mistaken in general radiance terms. I've always
> >>>assumed
> >>> the sun is included.
> >>>
> >>> None of our submitted calculations have been questioned to date, so
> >>> assume that this is acceptable.
> >>> Hope this helps!
> >>>
> >>> Cheers.
> >>>
> >>> Chris Coulter
> >>> Senior Lighting Designer
> >>> Buro Happold Consulting Engineers
> >>> 100 Broadway, 23rd Floor
> >>> New York, NY 10005
> >>> Tel: 212.334.2025
> >>> Direct: 212.616.0254
> >>> Email: chris.coulter at burohappold.com
> >>> Website: www.burohappold.com
> >>>
> >>> -----Original Message-----
> >>> From: Lars O. Grobe [mailto:grobe at gmx.net]
> >>> Sent: Tuesday, June 19, 2012 4:21 AM
> >>> To: Radiance general discussion
> >>> Subject: Re: [Radiance-general] Current practice for LEED sky
> >>>modelling?
> >>>
> >>> Hi John,
> >>>
> >>> I am aware of that really nice overview. The critique of using an
> >>> impossible sky model is hard to question. Excluding the sun also means
> >>> that any technique  to make use of direct sunlight by e.g. redirecting
> >>> it deeper from the perimeter into the building is not accounted for at
> >>> all. So that is why I was wondering how folks doing their real-life
> >>>jobs
> >>> for LEED are handling the problem with the current standards in mind.
> >>>
> >>> Another question is whether direct sunlight, after it got redirected,
> >>>is
> >>> still direct sunlight in LEED terms.... or whether redirected means
> >>> indirect here and I could again include it... leaving me with a more
> >>> meaningful sky model (clear sky with sun, and only portions directly
> >>> entering the used spaces being locked out assuming users would block
> >>> them by sunshades) accounting for redirecting facades.
> >>>
> >>> I am not sure wether this is too much LEED-specific for the mailing
> >>> list, but I was really curious how Radiance folks is working around the
> >>> not-so-physically-based specifications of current LEED when setting up
> >>> simulations.
> >>>
> >>> Cheers, Lars.
> >>>
> >>>> There's a critique of daylight modelling for LEED and other codes
> >>> here:
> >>>>
> >>>>
> http://www.iesd.dmu.ac.uk/~jm/doku.php?id=academic:daylight-compliance
> >>>>
> >>>> It includes a discussion on sky models.
> >>>>
> >>>> Best
> >>>> John Mardaljevic
> >>>>
> >>>> Reader in Daylight Modelling
> >>>> Institute of Energy and Sustainable Development De Montfort
> >>>> University, The Gateway, Leicester, LE1 9BH, UK
> >>>> Tel: +44 (0) 116 257 7972
> >>>>
> >>>> jm at dmu.ac.uk
> >>>> http://www.iesd.dmu.ac.uk/~jm
> >>>> http://dmu.academia.edu/JohnMardaljevic
> >>>
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> >>>
> >>>
> >>>
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