[esp-r] Re: MZELWE Longwave Flux Messages

[Ferguson, Alex]

>This was caused by the choice of high exterior surface
>absorptivity and emissivity values, low specific heat, 
>and low thermal conductivity.

The low specific heat and conductivity, and the high absorptivity and
emissivity values translate into a small thermal time constant for the
state equation describing the temperature of the surface. The simulation
becomes unstable when the solution time step approaches (or exceeds)
this time step; increasing the time resolution may also produce more
stable simulations. 

- Alex 

-----Original Message-----
From: esp-r-bounces at lists.strath.ac.uk
[mailto:esp-r-bounces at lists.strath.ac.uk] On Behalf Of Lukas Swan (Dal)
Sent: Wednesday, October 15, 2008 8:02 AM
To: 'Holger Bertling'
Cc: esp-r at lists.strath.ac.uk
Subject: [esp-r] Re: MZELWE Longwave Flux Messages

Hi Holger,
I have seen this in simulations before as well. It means that the long
wave flux from the exterior building surfaces is greater than a typical
expected range. I added a bit of verbosity to the source code once and
found that it was always caused by my exterior surface temperature being
too high. This was caused by the choice of high exterior surface
absorptivity and emissivity values, low specific heat, and low thermal
conductivity.

Take a good look at the materials you are using and how they are
situated into the construction. Adjust some of these values and the
issue will likely decrease.

Lukas Swan
Dalhousie Univ.
Canada

-----Original Message-----
From: esp-r-bounces at lists.strath.ac.uk
[mailto:esp-r-bounces at lists.strath.ac.uk] On Behalf Of Holger Bertling
Sent: October-14-08 1:34 PM
To: esp-r at lists.strath.ac.uk
Subject: [esp-r] MZELWE Longwave Flux Messages

Dear All,

during my simulations I get a lot of these messages:

Wall-6:Raum_3 @ increment 31883
 This is considered high and a correlation will be used.
 <sky =  -222.7 <buildings = -145.3 <ground = -197.0
 MZELWE: a longwave flux of   -578.9 Watts has been calculated for
Wall-6:Raum_1 @ increment 31884
 This is considered high and a correlation will be used.
 <sky =  -228.3 <buildings = -147.9 <ground = -202.8
 MZELWE: a longwave flux of   -496.6 Watts has been calculated for
Wall-6:Raum_3 @ increment 31884
 This is considered high and a correlation will be used.
 <sky =  -197.3 <buildings = -126.0 <ground = -173.3
  50 %   complete; expected finish time : Tue Oct 14 18:14:36 2008
 MZELWE: a longwave flux of   -538.3 Watts has been calculated for
Wall-6:Raum_1 @ increment 79966
 This is considered high and a correlation will be used.
 <sky =  -213.7 <buildings = -136.3 <ground = -188.3
 MZELWE: a longwave flux of   -655.9 Watts has been calculated for

Does anybody know,
what that means
and if its bad or OK?

Thanks in advance,
Holger


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