[TRNSYS-users] Trnsys 16 and 17 comparison - very different energies!

David BRADLEY d.bradley at tess-inc.com
Tue Apr 30 09:36:28 PDT 2013


   We did indeed change the behavior of Type11 with Trnsys17 back to 
what it had been long ago. The issue at hand is that when there is no 
flow through the diverter, what should the output values be set to 
(specifically the outlet temperatures)? Some claim that the output value 
should be set to the input value when there is no flow. Others would 
prefer the last calculated value of the output to be held until flow 
starts. This causes issues if controls are based on the outlet 
conditions of the diverters. There is not really a correct answer; it is 
just a matter of the assumption that you wish to make when writing the 
model. Our reasoning was that the temperature of the diverter should go 
to the inlet temperature so that there is not a temperature difference 
across the diverter under no-flow.

   If you are seeing a dramatic change in energy between the two 
versions, that is an indication that your controls are not operating the 
same between the two. Usually, systems that exhibit this behavior are 
systems that are low on thermal capacitance (i.e. there aren't enough 
pipes modeled in the various hydronics). Low- or no-capacitance hydronic 
loops react unrealistically quickly to control decisions and can become 
unstable. I would be curious to know whether you see the same energy 
differences between the v16 and v17 simulation if you add piping to your 
flow network.

Kind regards,


On 4/30/2013 10:48, Marco Noro wrote:
> Dear Trnsys-users,
> I have opened a .tpf project that I had built and run in Trnsys 16 
> with the new release Trnsys 17.
> With my great surprise, the energy balances (it is a solar cooling 
> plant) of the same project with the two Trnsys releases are very very 
> different.
> I realized that the mass flows are different, and in particular I 
> think that type 11 behaves in a different way in trnsys 16 and 17.
> The problem is that in my project a have a lot of diverter, mixer, 
> ecc., so: how can I solve this problem? That is, the same project 
> should behave in the same way!
> I add that the problem could be also (or) in type 2 behaviour in the 
> two trnsys releases...
> Thank you for your cooperation!
> Best regards
> Marco Noro
> //
> /***************************************///
> Marco Noro, PhD
> Assistant Professor in Applied Physics
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Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI  53703 USA

d.bradley at tess-inc.com


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