Psi - value calculation (linear thermal transmittance)
Alexandra Kalymniou
Hello! I am familiarising myself with THERM and I have difficulty understanding where I take the heat flux (Q) from the results so I calculate the psi-values. Q has W/m as units but in the results I can only find the heat flow in W and the heat flux is given in W/sqm. Can you please help me understand which values I should take? I have added images from the results for a window jamb interface with an sfs wall, with adiabatic bc where the window frame touches the reveal. Any help is much appreciated!!
Reichard, Georg
You may want to look at https://www.youtube.com/watch?v=QWdrFqZM1a8.
This introduction into psi-value calculation is a first step to understand how a 2-D simulation is a linear extrusion of the problem that you try to solve.
I.e. you actually “measure” the averaged heat flux along an edge for a 1-unit (1m or 1ft) height of extrusion of the problem, and the read flux is then per square area (length of the edge x 1 unit high).
Admittedly, the problem in a window detail is a bit more complex than a simple corner, as you have to types of constructions meet in the same plane.
I always meant to do another video to show how this is done as I typically teach it in the classroom but didn’t get around to it yet.
Take a look at the attached lecture slides – I know they are not narrated but can give you a better idea of what we do with psi-values.
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