[Virtual-sim] Low DF-values with Radiance

Nick Caton ncaton at smithboucher.com
Mon Sep 28 08:29:24 PDT 2009


Hi Erik,

 

I'm not familiar with the limitations/capabilities of the IES Radiance tool (still looking for a vendor in the US that can send me some kind of trial), but I may be able to offer some suggestions based on my limited daylight modeling experience:

 

-          To clarify, is it 12% of your wall area that is windows?

-          Again, not sure of the IES Radiance's operation, but when you say 'white' floors/ceiling and 'gray' floors, what reflectances are being modeled (i.e. 20/50/80%?)

-          Consider the hour/month being modeled, along with the orientation and location on the globe.  Perhaps you're modeling an instant in time where there is little-to-no direct sunlight on your glazing?  

-          I am also approaching learning daylight modeling from an energy-modeler's perspective:  For daylight studies, I try to give myself an idea of what should be going on first before "crunching the numbers" by building a simple model in Google Sketchup, located/oriented on the globe, and playing with the simplified daylighting tools to see how the sun strikes the building through the year.  With practice I'm sure this will become more intuitive, but until then I've learned not to rely on my intuitions!

-          A general heads-up that won't solve your immediate concern:  a visible transmittance (what IES Radiance calls "transparency" may be something else) of 0.9 is not unheard of, but pretty high for exterior envelope glazing... when I do daylighting/rendering studies I usually go no higher than 0.8 or so unless I have actual product specs in hand.

 

~Nick

 

 

 

 

NICK CATON, E.I.T.

PROJECT ENGINEER

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

Check out our new web-site @ www.smithboucher.com 

 

From: virtual-sim-bounces at lists.onebuilding.org [mailto:virtual-sim-bounces at lists.onebuilding.org] On Behalf Of Erik Eriksson
Sent: Monday, September 28, 2009 10:10 AM
To: Paul Carey
Cc: virtual-sim at lists.onebuilding.org
Subject: Re: [Virtual-sim] Low DF-values with Radiance

 


Hey, 

Yeah, I've tried that. With more or less the same result.
I'm quite new to this with lighting calculations. I'm more used to energy performance. 
So I cant really say if the values are correct or not. 

Best regards 

E r i k   E r i k s s o n 

Energy specialist and project manager
________________________________
White project & environmental management

Box 4700
116 92 STOCKHOLM
Phone: +46(0)8-402 26 77
Fax:      +46 (0)8-402 25 10
Visit:     Östgötagatan 100
http://www.white.se <http://www.white.se/> 

We are certified according to ISO 9000 and 14 001 



From: 

Paul Carey <paul at zed-uk.com> 

To: 

Erik Eriksson <erik.eriksson at white.se> 

Cc: 

"virtual-sim at lists.onebuilding.org" <virtual-sim at lists.onebuilding.org> 

Date: 

2009-09-28 17:06 

Subject: 

Re: [Virtual-sim] Low DF-values with Radiance

 

________________________________




Erik 

Try carrying out a model for one room at a time. The results tend to be quite different. 

Cheers 
Paul 



Sent from my iPhone 

On 28 Sep 2009, at 15:55, Erik Eriksson <erik.eriksson at white.se> wrote:


Hi all, 

I'm doing some daylighting studies with RadianceIES with a model I've imported from revit. The model seems to have been imported just fine. 
However I'm getting very low DF-values. 
The rooms I've been studying are rectangular cellular offices with about 12% of the floor area consisting of windows. 
The results show that approx 5-10% the area of a working plane at 0,8 m above the floor has a DF-value of 1.2 %. 
This feels like a very low number. The window transparancy is 0,9 and all the walls are white colored. The ceiling is white and the floor is gray. 

Does anyone have a suggestion as to what might be wrong or if these values seem ok. 

Thanks in advance 

Best regards 

E r i k   E r i k s s o n 

Energy specialist and project manager
________________________________
White project & environmental management

Box 4700
116 92 STOCKHOLM
Phone: +46(0)8-402 26 77
Fax:      +46 (0)8-402 25 10
Visit:     Östgötagatan 100
http://www.white.se <http://www.white.se/> 

We are certified according to ISO 9000 and 14 001 
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