[Radiance-general] Approximating the gross daylight flux through venetian blinds

[George Chadwick]

John -

 

> ANALYSING RADIATION TRANSPORT THROUGH 

> COMPLEX FENESTRATION SYSTEMS
> N.S. Campbell and J.K. Whittle


Thanks for that.

 

Interestingly the v. helpful C & W paper, although 

expressing sentiments that are bang on target, 

seems to compare one simulation with another, 

but not with real-world empirical data, unless I’m 

missing something. 

 

Maybe up to some point, comparisons of their 

Monte Carlo results with some similar simulation 

in Radiance could be interesting/useful, but surely 

not as useful as comparison with some real-world 

empirical data. 

 

Desperate for any kind of confirmation, my very 

rough lux-meter measurements of office blind 

overall transmission on an overcast London 

day compared tolerably with their simulations. 

 

I’m hoping some better real-world data will 

come to light eventually.

 



> .... just how useful is a daylight factor 

> evaluation for the scenario you describe.  

> Surely, the blinds are there also to control

> direct sunlight?  Perhaps even it is their 

> main purpose.

On the subject of control of direct sunlight by 

blinds; despite having more than a suspicion 

that you know more about daylighting than 

I do, here goes:

 

The reason I said I was ‘not interested’ in 

direct sunlight in those studies was that for me 

at least, in the UK, the ‘overcast sky’ is the most 

useful environment to apply in daylight studies 

at the early stages of building design development. 

 

It allows alternative architectural designs to be 

compared for degrees of compliance with 

particular published UK CIBSE and BCO 

criteria so as to merit the alternatives' 

daylighting.

 

I find that the usual objective for these sorts of 

study is to find the daylight factor with ‘venetian 

blinds down, slats horizontal, overcast sky’.

 

The control of direct sunlight by the venetian 

blinds need not figure in these early simulations, 

despite that being their major function.

 

Any fixed solar shading does of course have 

to be modelled reasonably well, as do the 

relevant parameters for the solar transmission 

of the façade and glazings; the geometry and 

reflectance of the building model and its context. 

 

Agreed nevertheless that if one could develop 

a function to simulate blinds, then not allowing 

the direct factor to be simulated would be 

somewhat perverse. 

 

Regards, George Chadwick


		
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