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

[coolbilly1999 at gmail.com]

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 
Sent: Monday, February 20, 2012 8:53 AM
To: Billy Chen ; 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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