Re: [TRNSYS-users] Time step for Pollution solver

["Diego A. Arias" <daarias@wisc.edu>]

Dear Stefan,

The problem that you are seeing when you set the time step to less than 
1 minute may be due to the time base of the wall transfer functions.  It 
is possible that you have a wall that is relatively thin, and when you 
reduce the time-step the thermal behavior can be replaced with a 
resistance, neglecting the thermal mass.  An explanation of the transfer 
function can be found in Volume 6, part 2, section 2.1.6.

If you want to email me the project files, I will be glad to take a look 
at them.
Best regards,

Diego


Stefan de Kool wrote:

> Hello,
>
>  
>
> I have a problem modelling pollutant flow. I have a simple one 
> zone-building with inhabitants producing CO2. I use this concentration 
> to control a fan. The problem is that when I run the simulation, I get 
> the following warning:
>
>  
>
> ***** WARNING ***** UNIT 37 TYPE 56, TIME =   4.188E+00
>
>  COMIS MESSAGE  ***** WARNING *****
>
>  Pollutant transport solver : Small timestep
>
>  needed (Tau < 10 sec), but is limited to 1 sec
>
>  
>
> appearing at every time step. But, when I decrease the time step below 
> 56.25 sec (0.5^6*1hr), I get a range check error during the simulation 
> (the first couple of hours are plotted before the error). Does anyone 
> have experience with this? What causes the error? And is such a small 
> time step always needed when simulating pollutants or does it depend 
> on e.g. the zone volume?
>
>  
>
> Thanks a lot,
>
> Stefan de Kool
>
>  
>
> Cauberg-Huygen Raadgevende Ingenieurs
>
> Lokatie Rotterdam
>
>  
>
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>
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--

Diego A. Arias
TRNSYS Coordinator
Solar Energy Laboratory
University of Wisconsin - Madison
1500 Engineering Drive
Madison, WI 53706