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Re: [TRNSYS-users] Adiabatic wall


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:

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.

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

-- _________________________________________________________

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@xxxxxxxxxxxxx

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