Modelling of Double Skin Facades in HB



Hello All,

I am currently assessing the performance of double skin facades comparing them with standard single skin facades. The aim is to see what is the energy consumption (cooling loads etc.) with different options.

I wanted to ask to the community here what is the most appropriate approach to model double skin facades in HB, how to account for the actual properties of blinds located in the cavity etc.

Is the best option we have to follow the approach in the example below?,-3.8445581267411058

How can we apply specific material properties (for example, LT, g-value) using the Energy Plus Window Shade generator?

Could the double skin be modeled as BSDF material imported from Window? How could we in this case make the double skin dynamic (e.g. blinds up and blinds down)?

I will probably have further and specific questions as I go on but I wanted to check first what is the suggested approach to model this kind of facade.

Thank you in advance for your help,



Hello All,

I have looked into the example below:,-3.8445581267411058

I have a few questions which also include some more generic ones not strictly related to a double skin facade:

  • Why would we use ‘Air Walls’ in the component ‘solve adjacencies’? This removes the internal glass wall and indeed looking at the cooling loads we get very high values (I am considering the climate of Hong Kong);

  • Why is the ‘stack discharge coefficient’ set to 0.286? It is slightly different than the recommended coefficient options listed in the component;

  • Is there not a way of creating a double or triple glazed unit with argon filled cavity (e.g.the typical 90% Argon and 10% Air) using the air gap component? Are we limited to use the energy plus window material? Is the alternative to import a double glazing unit from WINDOW? Would mass be taken into account in this case?




Hi Carmelo

I’m am interested to find out more about this too, I am going to be looking at daylight and double skin facades for my master’s thesis, but I need to have some energy analysis as well. I have spoken to a few people and they said HB might have some limitations with fluid dynamics involved in the cavity between the two skins, where air stratification must be modelled. I don’t know if you have found any information on this?




Hello Julie,

It seems I didn’t get any replies on this topic.
I think the right tool depends (of course) on what is the scope of the analysis. If you have to perform an energy balance and understand the consumption of your building then I feel that the tools within HB are appropriate. To get additional accuracy in the analysis you can also split the double skin facade in multiple zones (to better model the change in temperature due to the stack effect and natural convection). I think CFD is definitely the right tool to use if you want to ‘accurately’ assess the temperature distribution within the cavity. This may be relevant when you want to assess maximum temperature are within acceptable limits. For example in double skin facades you typically have motors for the blinds which will start failing above certain temperatures; gaskets and seals in the facade are also sensitive to very high temperatures (e.g. above 80 degC). Interlayers used in glass build-ups (especially PVB) are also sensitive to high temperatures. When you talk about CFD for HB you must refer here to Butterfly and OpenFOAM. I haven’t used this plug-in much myself really but For CFD purposes I have heard the same limitations you mention in your post. However, from what you are saying you may not really need CFD? For your reference, I used quite a while ago COMSOL to model the temperature distribution in the cavity of a mechanically ventilated double skin facade (please see the link
Hope this helps!




Hi Carmelo,
Thanks very much for your reply I will take a look at the link,
kind regards Julie