[Radiance-general] lighting simulation of blinds in Energy Plus vs. Radiance

[Greg Ward]

Hello Svetlana,

Naturally, asking on the Radiance mailing list, you're going to hear  
people say Radiance is the most accurate.  In your case, I would say  
the 10% error is going to be overshadowed (no pun intended) by the  
variability of daylight.  Specifically, it is very important to  
consider the weather data used as your basis in determining exterior  
daylight conditions.  Even getting within 10% of measured  
illuminances requires the use of measured sky distributions, which  
are almost never available.  So, I'd say this accuracy is based on  
the assumption that your sky matches the standard CIE model, which of  
course it won't if it's a real sky.  Radiance would fare no better.

Annual simulation requires quick calculations, which is not really  
Radiance's strength.  I know that Rob Hitchcock (the author of  
DElight) has put a lot of energy into his fenestration calculations,  
so if you aren't getting the output you expect, I'd take a closer  
look at the input as a first step.

Cheers,
-Greg

> From: Svetlana Olbina <svetlanaolbina at yahoo.com>
> Date: June 5, 2008 10:34:35 AM PDT
> Hello, All,
>
> We are doing research on blinds that we call “split controlled  
> blinds”.
>
> Basically, we divided a window in three sections in a vertical  
> direction.
>
> In each window section we use the same type of the blinds but the  
> slats have different tilt angles in each section (for example, 0  
> degrees in the upper part (completely open) , 15 degrees in the  
> middle part and then 90 degrees in the lower part (completely closed).
>
> We plan to do both energy and lighting simulations for these  
> blinds. For the energy simulations we use Energy Plus.
>
> Energy Plus also performs lighting simulations.  I wanted to ask  
> for your opinion about accuracy/validation of Energy Plus when it  
> comes to lighting simulation.
>
> I have read that Energy Plus has integrated DElight software  
> (radiosity based lighting simulation software) and that  
> measurements are within 10% error? Is this margin of error acceptable?
>
> Our building is very simple (10’x15’ in the plan), and it has a  
> 6'X6' window on a 10' X 11' wall. We expected sufficient
> levels of illuminance  for this room but we got low illuminance  
> value of 270 lux at the workplane close to the window.
>
> I am concerned is that either Energy Plus is not accurate enough or  
> we have some error in our input.
>
> How would you compare Radiance and Energy Plus (or DElight) when it  
> comes to simulation of blinds?
>
> We are new to Radiance and work already in Energy Plus, so we want  
> to see if we can use Energy Plus for lighting simulation instead of  
> Radiance.
>
> Or Radiance is still the most accurate tool for lighting simulations?
>
> Thank you.
>
> Svetlana