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

[jeannieboef]

Jeff, that's been bugging me for a while...most equipment is specified  
at a "rated" condition. Take a fan for example: the controller will  
accept a value greater than 1. I assumed 1 is the fan flow at rated  
pressure and efficiency. less than 1 and greater than one will ride  
the fan curve defined by the fan coefficients to deturmine the power  
draw at flowrates=ratedflowrate*control signal. I expect pumps to work  
the same and for that matter most equipment. The term "maximum" could  
possibly be "rated maximum". coils should be no exception. How far a  
system is allowed to exceed rated maximums should be known to the  
engineer. I allow my fans to go at 1.3 of max rated flow, but design  
the system to work at 1.

is this understanding of Trnsys models correct?

regards

jean

Sent from my iPhone

On 28.11.2012, at 18:10, Jeff Thornton <thornton at tess-inc.com> wrote:

> <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
>
> E-Mail: 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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> TRNSYS-users at cae.wisc.edu
> https://mailman.cae.wisc.edu/listinfo/trnsys-users
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