[Bldg-sim] Daylighting Program

Reinhart, Christoph reinhart at gsd.harvard.edu
Mon Mar 9 07:16:26 PDT 2009


Dear Mark and others,

 

Interesting threat. Michael listed a series of workflows that one can
use to analyze a SketchUp scene using either Radiance or 3ds Max
Design/Mental Ray. Michael also pointed out that these two simulation
engines have been successfully validated based on measured indoor
illuminances. Before picking any of these workflows I recommend that you
first carefully decide what you actually want to calculate using
daylight simulations.

 

*         For a LEED 8.1 Daylighting Credit compliance simulation most
of the work flows described by Michael should work since the 'old' CIE
clear sky as well as the CIE overcast sky (for daylight factor
calculations) are supported by Radiance and 3ds Max. If this is your
objective it is worthwhile mentioning that there are many designs that
fail the LEED glazing/daylight factor requirement according to
simulations but meet it via the spreadsheet method from the LEED
technical manual (see p.32:
www.gsd.harvard.edu/people/faculty/reinhart/documents/DiffuseDaylighting
DesignSequence.pdf) .

*         For physically based images both engines can be used (pay
attention that you actually use Mental Ray as the engine for your 3ds
Max simulations). Mental Ray tends to be faster than Radiance but
Radiance offers richer analysis capabilities including various glare
indices (if one is willing to use Radiance via the command line).

*         Climate-based daylighting metrics have been proposed to be
superior design measures than the daylight factor
(http://irc.nrc-cnrc.gc.ca/pubs/fulltext/nrcc48669/nrcc48669.pdf
<http://irc.nrc-cnrc.gc.ca/pubs/fulltext/nrcc48669/nrcc48669.pdf> ) and
IESNA and CIE are currently working on benchmark levels for these
metrics. To calculate a climate-based metric you can use Daysim, SPOT
and (in principal) even 3ds Max. The caveat for 3ds Max is that the
calculations would currently take a long time (page 29
www.autodesk.com/us/3dsmaxdesign/B3241.MentalRayValidation_v3.pdf
<http://www.autodesk.com/us/3dsmaxdesign/B3241.MentalRayValidation_v3.pd
f> ).

*         For integrated lighting-thermal simulations one can either use
a build-in method (e.g. in EnergyPlus or DOE2.1) or link the thermal
simulation program with externally calculated annual illuminance
profiles. The latter methods tends to be more accurate.

 

>>Ramana Koti wrote: I don't think the choice of materials that can be
assigned from within SketchUp is that comprehensive yet ... I'd be
interested in hearing from Christoph ... when we'll be able to assign
user created materials to surfaces within SketchUp before exporting to
DAYSIM.

We once had a good workflow from Sketchup 4 to Daysim via the 3ds format
that allowed the user to  use a custom material library in SketchUp to
automatically assign materials in Daysim. The 3ds export file format in
SketchUp 5 was unfortunately slightly changed so that this workflow is
not valid any more. I am now using Thomas Bleicher's earlier mentioned
SketchUp to Radiance exporter. I find the only 'hiccup' with this
approach to be that the exporter writes out all layers into separate
files which have to be individually imported into Daysim. I also have to
manually assign the materials, i.e. there is still room for improvement.

 

A general warning for any daylight simulations based on a SketchUp scene
is that SketchUp allows to assign different material properties to the
two surfaces of a polygon. This leaves room for errors since Radiance
only recognizes one material type per polygon.

 

Christoph

Christoph Reinhart, Dr. Ing. 

Associate Professor of Architectural Technology

Graduate School of Design - Harvard University

Gund Hall 331b, 48 Quincy Street, Cambridge, MA 02138, USA

t: 617 384 7269, f: 617 495 8916, reinhart at gsd.harvard.edu
<mailto:reinhart at gsd.harvard.edu> 

 

 

 

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