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

[David BRADLEY <d.bradley@tess-inc.com>]

Marco,

  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,

 David

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

 

 

 

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Marco Noro, PhD

Assistant Professor in Applied Physics

Department of Management and Engineering (DTG)  -  University of Padova

stradella San Nicola, 3  -  36100  Vicenza  (VI)  -  Italy

tel.   +390444 998704    -    fax   +390444 998884

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skype     nereo3

 

 

 

 

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