Thanks for doing the legwok, Ji! Here's the other paper I mentioned in that post:
http://tinyurl.com/cu6xgug
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
[email protected]
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
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<tel:303.275.4319>
[email protected]<mailto:[email protected]>
···
On 6/19/12 10:28 AM, "Ji Zhang" <[email protected]<mailto:[email protected]>> wrote:
On Wed, Jun 20, 2012 at 12:02 AM, Guglielmetti, Robert <[email protected]<mailto:[email protected]>> wrote:
On 6/19/12 9:41 AM, "Lars O. Grobe" <[email protected]<mailto:[email protected]>> 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" ><[email protected]<mailto:[email protected]>> 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<tel:303.275.4319>
[email protected]<mailto:[email protected]>
On 6/19/12 7:16 AM, "Chris Coulter" <[email protected]<mailto:[email protected]>> >>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<tel:212.334.2025>
Direct: 212.616.0254<tel:212.616.0254>
Email: [email protected]<mailto:[email protected]>
Website: www.burohappold.com<http://www.burohappold.com>
-----Original Message-----
From: Lars O. Grobe [mailto:[email protected]<mailto:[email protected]>]
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:
Institute of Energy and Sustainable Development;
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<tel:%2B44%20%280%29%20116%20257%207972>
[email protected]<mailto:[email protected]>
Institute of Energy and Sustainable Development;
John Mardaljevic | Loughborough University - Academia.edu
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