[Virtual-sim] Low DF-values with Radiance

Tue Sep 29 10:09:01 PDT 2009

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From: virtual-sim-bounces at lists.onebuilding.org [mailto:virtual-sim-bounces at lists.onebuilding.org] On Behalf Of Paul Carey
Sent: Tuesday, September 29, 2009 1:52 AM
To: 'Nick Caton'; 'Erik Eriksson'
Cc: virtual-sim at lists.onebuilding.org
Subject: Re: [Virtual-sim] Low DF-values with Radiance

Erik/Nick

I'd agree on the glazing spec thing don't go putting in very clear glass unless you are very sure that it's going to have those sorts of properties.  A check of the G value should help give you a guide to light transmittance.  Or just check out the Pilkington website or similar to give you a good idea, their selection tool (think it's called spectrum or something, a while since I've used it) is quite good for getting some ideas of what it will be like.

In terms of the daylight studies, they should always be carried out using the IEE overcast sky to assess daylight factors.  If you want to check out glare etc obviously use a different sky, but for DF calculations the overcast sky should be used.  The default positions of everything else in IES should be ok once you've set that up as it will work out the working plane levels based on that sky. 

Nick, you should be able to download IES for a trial from their website normally.  Just email in a request for keys and they should set you up with a trial.  If you haven't checked out DesignBuilder you might want to do that too (30 day trial available from their website).  Quite similar tool (front end slightly more sketchup like than IES), but uses energyplus instead.  Doesn't have the radiance link yet, but we keep pestering the guys there to get that link in.

Regards

Paul

From: Nick Caton [mailto:ncaton at smithboucher.com] 
Sent: 28 September 2009 16:29
To: Erik Eriksson; Paul Carey
Cc: virtual-sim at lists.onebuilding.org
Subject: RE: [Virtual-sim] Low DF-values with Radiance

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

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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/> 

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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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