[TRNSYS-users] Adiabatic wall

[Michaël Kummert]

Maurizio,

This was discussed recently on this list.
As noted by Xavier Casals, a "boundary = identical" wall will have the 
same AIR temperature on both sides. So the adiabatic plane is somewhere 
inside the wall, not at the "outside" (or "back") surface. In other 
words, the wall does not contribute to heat losses but it does 
contribute to the thermal inertia.

Matthias Rudolph mentioned a solution if you need an adiabatic surface 
at the "back" side of the wall:

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For boundary walls you can define a very small convective heat transfer 
condition > 0.001 W/m²K. For alpha < 0.001 you will receive direct 
contact (almost equivalent to > 999 W/m²K). We kept this for backwards 
compatibility.
So if you want to create a wall with mass towards the zone and the 
adiabatic condition on the back (not in the middle of the wall as in 
boundary identical mode), you might use following approaches
1. choose a low alpha e.g. 0.002 on the back of the boundary identical wall
2. define the wall adjacent to a ficitve zone with alpha_back = 999. In 
this fictive zone define a resistance only wall with alpha_front = 999 
and boundary identical to the back.
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Also, you should remember that the building model in Type 56 is 
non-geometrical. If you need a surface that does not exchange heat with 
the zone, just skip it! Compared to the solution here above it does have 
one drawback: the solar radiation distribution will be different (beam 
is distributed according to GEOSURF, so you can fix it, but diffuse is 
distributed according to absorptance weighted area ratios so it will be 
different if you "forget" a large surface in your room). Long-wave 
radiation will also be different since view factors are also 
approximated by area ratios. But depending on what you really want to 
simulate, just skipping a wall can be the solution.

Kind regards,

Michaël Kummert


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_________________________________________________________

Michaël Kummert

Solar Energy Laboratory - University of Wisconsin-Madison
1303 Engr Res Bldg, 1500 Engineering Drive
Madison, WI 53706

Tel: +1 (608) 263-1589
Fax: +1 (608) 262-8464
E-mail: kummert at engr.wisc.edu

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