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

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@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@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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