[TRNSYS-users] Type 512 (TESS): Mass balance warning message

[Flynn Ciaran]

Hi, it’s me again,

I looked more closely at the flow rates, on the cold side both the entering and exiting flows are equal, however on the hot side there seems to be some lag between the entering and exiting flow rates. I tried reducing the time step (from 0.1 to 0.01 hours) but the problem still persists…

Thanks for helping,
Ciarán


From: Flynn Ciaran
Sent: 29. marraskuuta 2012 10:32
To: 'thornton at tess-inc.com'; trnsys-users at cae.wisc.edu
Subject: RE: [TRNSYS-users] Type 512 (TESS): Mass balance warning message

Hi Jeff,

Thanks for your quick reply. I checked the connections and flow rates and they all seem to be ok. On the hot side I have a type 3b variable speed pump, on the cold side a Type 3d single speed pump, both of which have the same maximum flow rates. And this particular flow rate I used as parameter 4 of Type 512 “Rated flow rate of hot side”. I also connected the 6th output of type 512 to the control signal of the variable pump on the hot side of the exchanger..

I still get this mass balance problem. Any ideas what is going wrong?

Thanks,
Ciarán


From: trnsys-users-bounces at cae.wisc.edu [mailto:trnsys-users-bounces at cae.wisc.edu] On Behalf Of Jeff Thornton
Sent: 28. marraskuuta 2012 19:10
To: trnsys-users at cae.wisc.edu
Subject: Re: [TRNSYS-users] Type 512 (TESS): Mass balance warning message


<I am running my simulation with a type 512 heat exchanger and I get the following warning message (no convergence errors, just warnings) at the end of my simulation (time step: 0.1 hour):>

Type 512 has internal controls to vary the speed of the hot-side flow rate through the heat exchanger.  I'm guessing that you're hooking up a pump to this heat exchanger and the flow rate into the HX is not the flow rate out of the HX - as 512 is setting the flow rate.  The best way to use 512 is to use a variable speed pump model and make sure the maximum flow rate parameter for both the pump and HX models are identical.  Then put the pump either upstream or downstream of the HX and connect the 6th output of the heat exchanger model to the control signal for the pump - so that they both produce the same flow rate.



Jeff



---

Jeff Thornton

President - TESS LLC

22 N. Carroll Street, Madison WI USA 53703

Office: (608) 274-2577  Fax: (608) 278-1475

www.tess-inc.com<http://www.tess-inc.com>

E-Mail: thornton at tess-inc.com<mailto:thornton at tess-inc.com>



On 11/28/2012 6:11 am, Flynn Ciaran wrote:
Hello,

I am running my simulation with a type 512 heat exchanger and I get the following warning message (no convergence errors, just warnings) at the end of my simulation (time step: 0.1 hour):

*** Warning at time       :     39384.000000
    Generated by Unit     :    45
    Generated by Type     :   512
    Message               : Heat exchanger mass balance failed during 112810 time steps. Please check the connections.

I do not understand what could be the reason for this. I have gone through my connections and they all seem fine (I do not get this problem with heat exchanger type 91).

Thanks for your help,
Ciarán

----------------------------------------
Ciarán Flynn
Research Scientist

Aalto University
Department of Energy Technology
P.O.Box 14100, 00076 Aalto
Otakaari 4, 02150 ESPOO

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