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

[Jeff Thornton]

<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?> 

Your
summary of the rated conditions in TRNSYS is correct for the majority of
the models available - but I will warn you that some of the older models
do not allow the input control signals to go greater than 1. So your
rated condition in those models IS the maximum condition allowed. As
with any model, when you create the power coefficients you should make
sure the resulting curves are valid over the entire range provided.


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 1:38 pm, jeannieboef wrote: 

> 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 [5]> wrote:
> 
>> 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 [1]_ 
>> 
>> _E-Mail:
thornton at tess-inc.com [2]_ 
>> 
>> 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_
> 
>>
_______________________________________________
>> TRNSYS-users mailing
list
>> TRNSYS-users at cae.wisc.edu [3]
>>
https://mailman.cae.wisc.edu/listinfo/trnsys-users [4]



Links:
------
[1] http://www.tess-inc.com
[2]
mailto:thornton at tess-inc.com
[3] mailto:TRNSYS-users at cae.wisc.edu
[4]
https://mailman.cae.wisc.edu/listinfo/trnsys-users
[5]
mailto:thornton at tess-inc.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/trnsys-users-onebuilding.org/attachments/20121128/42bf9f1d/attachment-0001.htm>