[TRNSYS-users] [Fwd: Stability criteria not fullfilled]

[Technical Support]

Thomas,
  There are two ways that Type56 can treat a wall. Normally, it accounts
for the mass, specific heat, and conductivity of each layer of materials
in the wall and it constructs a series of coefficients that are applied
to a transfer function that models how energy travels through the wall
with respect to time and to varying conditions.    The algorithm
accounts for the wall's ability to store thermal energy. If, however,
the wall is too massive or not massive enough, the algorithm that
generates the transfer function coefficients breaks down. For thinner
(non-massive) walls such as doors or perhaps a metal roof, you can
sometimes decrease the Type56 timebase in TRNBuild (click on the
"outputs" button in the main project window). If that doesn't work, then
Type56 can treat the wall as if it were a pure thermal resistance. In
this case, the wall has no ability to store energy and the energy
transfer is steady state.

  I am not aware of a solution for what to do if the wall is too massive,
which, if you have 0.5m of insulation, it might well be. If you are
dealing with a ground coupled slab, there are more appropriate ways of
modeling this than with a large effective block of insulation underneath
the slab connecting the slab temperature to ambient temperature.
Kind regards,
 David




>
> ---Technical Support Team
Thermal Energy System Specialists, LLC
2916 Marketplace Dr, Suite 104
Madison, WI 53719
techsupport at tess-inc.com

>----- Original Message --------
> Subject:         [TRNSYS-users] Stability criteria not fullfilled
> Date:         Sun, 30 Mar 2008 20:29:50 +0200
> From:         T. Tian<thomas.geier3 at freenet.de>
> Reply-To:         thomas.geier3 at freenet.de
> To:         trnsys-users<trnsys-users at engr.wisc.edu>
>
>
>
> Hallo Trnsys Usertrnsys-users,
>
> I found one message from internet as blow:
>
> "Actually with your defined wall ( heavy, very well insulated) the
transfer function
> method reaches its limits.
> We would suggest to simulate only the concrete part as thermal mass
while the
> insulation part can be ".
> As the insulation material has a low thermal mass this will not create a
big error."
>
> I am newbie with TRNSYS. Can someone explain to me this more: "simulated as
> resistance"? What should people do if the wall has more than 50cm
insulation in
> Trnsys?
>
> Thanks a lot
>
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