sDA - dynamic shading

[David_S]

We would like to asses the spatial dayligth authonomy (sDA). Following the LM 83-12 documentation (reference for sDA calculations), there is a requirement for dynamic modeling of shading, specifically:

All exterior windows must be modeled with blinds, unless (condition X, Y)... If both of these criteria (X, Y) are not met, then blinds must be modeled. Blinds shall close whenever more than 2% of the analysis points receive direct sunlight.... Direct sunlight is defined as an interior horizontal measurement of 1,000 lux or more of direct beam sunlight...

I haven't found any way, how the dynamic shading can be set up within the Radiance module (I am aware of the local shading feature within the construction database, but in our understanding this works only for thermal applications).

Can dynamic shading be achieved with the IES VE Radiance?
If not, would there be any practical workaround?

Many thanks for any comments on this.

[RossThompson87]

Hi David,

I haven't actually done this in radiance but I have with DaySIM.

It should be possible to run a simulation with the blinds fully down, and a separate one without them.

Get the results (lux levels for each grid point) into Excel. (I don't actually know how to do this with IES, but I suspect radiance saves a file somewhere with this data in).

Then with Excel you can combine the two tables based on your criteria for the blinds opening / closing.

From the combined lux levels table you calculate your Daylight Autonomy result, or any other metric you choose to use.

As a bit of a warning the processing in Excel is tricky as so much data is involved.

I hope this helps. Maybe someone else knows an easier way.

Ross

[David_S]

Hi Ross,
Thank you for the prompt answer and suggestion, I will give it a go
David

[David_S]

Hi Ross,
I have been playing with the method you have suggested.
I understand that it is required to run simulations with and without blinds.

Also, in my understanding, the 2% of area >1000lux threshold (i.e. denoting when the blinds should go down) should be assessed under
direct sunlight, which is in LM-83-12 defined as:
- ligth directly from the orb of the sun, including effects of the atmosphere and cloudiness based on TMY data
- taking to account external and internal obstructions
- not taking to account inter-reflections (i.e. zero bounce analysis).

Now, when I access the temporal (hourly) data in IES, there are just three types of illuminance available for each point:
- CIE Overcast sky
- Sunny sky
- DA data

For the sDA blinds up an down simulations I have used the DA data (assuming that the DA stands for daylight autonomy). But for the direct sunlight (driving the 'switching' of blinds as per the above), it seems to me that IES does not provide access to the data (while at the same time, as this model is used for ASE calculation, I presume that IES can do it too?).

So:
- Would anyone comment how to access the ASE termporal data, or if this can be done in IES at all?
- If not, could the Sunny sky data be used as a (reasonable) substitute? (but then not sure about the TMY cloudinnes and how the model treats inter-reflections?)..

I understand Ross that you haven't used IES for this, but could somebody else please comment / clarify?
Thank you