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

Tue Jun 19 08:41:10 PDT 2012

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
>> 
>> _______________________________________________
>> Radiance-general mailing list
>> Radiance-general at radiance-online.org
>> http://www.radiance-online.org/mailman/listinfo/radiance-general
>> 
>> 
>> 
>> _______________________________________________
>> Radiance-general mailing list
>> Radiance-general at radiance-online.org
>> http://www.radiance-online.org/mailman/listinfo/radiance-general
> 
> 
> _______________________________________________
> Radiance-general mailing list
> Radiance-general at radiance-online.org
> http://www.radiance-online.org/mailman/listinfo/radiance-general