Stone wall construction and position of window surface

[Giorgos Gourlis]

Hi,
I am modeling a building with thick stone walls and I would like to ask about two issues that I came across.

1. I wanted to ask which is the proper way to describe a stone wall with mortar mix between the stones' joints. In case I have information of U-values etc individually for each component, would an approach that the whole thickness of the wall constists of 90% of stone and 10% of mortar with the stone layer towards the exterior and mortar towards the interior be correct? Have you any experience on the subject?

2. My second question is about the position that Energy Plus places a window surface on a thick wall construction.
In my case the wall has a thickness of 60cm and I would like the windows to be on the inner side of the construction. I haven't found an option that sets the position of sub-surfaces and I would like to ask if Energy Plus places the window sub-surface at the midle of the construction of the hosting surface.
This is crucial because the thicknes of the wall acts as shading for the window. I was thinking that if I assume that the window is in the midle, I could add an overhang, sized half of the wall's thickness in order to achieve the whole length.

Thanks in advance for your time,
Giorgos

[farhang.tahmasebi]

Hi,

1. I didn't completely understand your description, but if you can imagine it as a 2D geometry, the easiest way is to calculate the average U, based on the area and U-value of each element: Um = U1A1 + U2A2 / A1 + A2.

However, in advanced levels, we derive this kind of U-Values by modeling two-dimensional heat-transfer effects in tools like LBNL Therml, Antherm. 

2. In EnergyPlus, in terms of geometry, you just have surfaces and not thick walls. I don't know why you are concerned about the position of windows. If it's about thermal bridges, EnergyPlus does not take 2D or 3D heat transfer into account. If it is about shading, you may put some extra shading surfaces. 

Best,

Farhang