[TRNSYS-users] Need helps to solve the absorption chiller (Type677) issue

[David BRADLEY]

Billy,
  I typically put a buffer storage tank in those loops instead of a 
pipe. The idea is the same. The volume of the tank (or pipe) should be a 
little more than the volume of fluid that the pump in the loop can 
transfer in one timestep.
Best,
  David


On 2/20/2012 22:16, coolbilly1999 at gmail.com wrote:
> Hi Matt,
> Thanks for the detailed explanation. I will try to shorten the 
> timestep. Actually, I also tried adding a pipe between the cooling 
> coil and chiller to store adequate flow as mentioned in the 
> documentation which I neglected before. And it works pretty well and I 
> will look into the other warnings you mentioned. Thanks for your help 
> again.
> Best regards,
> Billy
> *From:* Matt Duffy <mailto:duffy at tess-inc.com>
> *Sent:* Monday, February 20, 2012 8:53 AM
> *To:* Billy Chen <mailto:coolbilly1999 at gmail.com> ; 
> trnsys-users at cae.wisc.edu <mailto:trnsys-users at cae.wisc.edu>
> *Subject:* Re: [TRNSYS-users] Need helps to solve the absorption 
> chiller (Type677) issue
> Billy,
>
> I looked at your listing file, and I noticed other important things 
> about your simulation. First of all, the timestep you are using is 
> much too large. You will notice in the TESS HVAC Solar Absorption 
> example, the timestep is 5 minutes (note the equation in the control 
> cards to implement this) in order to consider the control decisions 
> and flow rates during that timestep. When using a large timestep, an 
> extraordinary amount of fluid is being sent through your system, and 
> if you are not simulating adequate capacitance or storage in that 
> loop, it will lead to components not converging. Also, please note the 
> other warnings at the end of your listing file about the independent 
> variables being above or below the specified range in the performance 
> data files. The TRNSYS data interpolation routine does not 
> extrapolate, so if you send it an independent variable that is not 
> within the specified range, it will use the dependent variable at that 
> end(or beginning) of the range and not extrapolate.
>
> Best regards,
>
> Matt Duffy
>
>
> *----- Original Message -----*
> *From:* "Billy Chen" <coolbilly1999 at gmail.com>
> *Sent:* Fri, February 17, 2012 17:22
> *Subject:* [TRNSYS-users] Need helps to solve the absorption chiller 
> (Type677) issue
>
> Hi TRNSYS users,
> I am building an absorption chiller model for a medium office, and I 
> used the similar components from the TESS example (Restaurant with 
> absorption chiller). However, when I ran the simulation, I got tons of 
> warnings (from SYS Message 441), and the simulation terminated because 
> it exceeded the limit of warnings. The warning said as below:
> *** Warning at time       :      3717.000000
>     Generated by Unit     : Not applicable or not available
>     Generated by Type     : Not applicable or not available
>     TRNSYS Message    441 : The inputs to the listed units have not 
> converged at this timestep. The values at the last iteration will be 
> used and the simulation will proceed.
>     Reported information  : UNITS: 12  13  18
> UNIT 12 is Type 677 double effect chiller
> UNIT 13 is Type 144 pump
> UNIT 18 is Type 697b cooling coil
> I checked the input units and I can't figure out the problem. Could 
> someone give me some advice?
> And I also found out a problem when I ran the TESS Restaurant example, 
> the chilled water outlet temperature is always going up over 100 
> degree C. But the temperature from the air temperature  from cooling 
> coil looks reasonable. It confuses me a lot. Does anyone find this 
> problem before and have any suggestion on that?
> I attached the LST file and the plot for the chiller water temp. I 
> really appreciate any help.
> Best regards,
> Billy
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-- 
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI  53703 USA

P:+1.608.274.2577
F:+1.608.278.1475
d.bradley at tess-inc.com

http://www.tess-inc.com
http://www.trnsys.com

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