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What does the EnergyPlus warning "Inside surface heat balance did not converge" mean?

asked 2018-03-14 16:16:27 -0500

Molly Curtz gravatar image

updated 2018-03-16 09:17:05 -0500

I have an Energy Plus file with the following warnings in the .err report:

 ** Warning ** Inside surface heat balance did not converge with Max Temp Difference [C] =2.501E-003 vs Max Allowed Temp Diff [C] =2.000E-003
 **   ~~~   **  During Sizing, Environment=SUMMER DESIGN DAY IN UNTITLED (01-01:31-12) JUL, at Simulation time=07/15 15:00 - 15:10
 ** Warning ** Inside surface heat balance did not converge with Max Temp Difference [C] =2.401E-003 vs Max Allowed Temp Diff [C] =2.000E-003
 **   ~~~   **  During Sizing, Environment=SUMMER DESIGN DAY IN UNTITLED (01-01:31-12) JUL, at Simulation time=07/15 17:10 - 17:20
 ** Warning ** Inside surface heat balance did not converge with Max Temp Difference [C] =2.247E-003 vs Max Allowed Temp Diff [C] =2.000E-003
 **   ~~~   **  During Sizing, Environment=SUMMER DESIGN DAY IN UNTITLED (01-01:31-12) AUG, at Simulation time=08/15 15:20 - 15:30

I'm not clear what is indicated by this, if I need to worry about it or not, and if I do need to worry about it, what I might try to correct the problem.

Additionally, I'm confused that the recurring error summary at the bottom of the .err file says the error occurred zero times during Sizing, but the prior error messages indicate that they occurred during Sizing?

  ************* ===== Recurring Error Summary =====
  ************* The following recurring error messages occurred.
  *************
  *************  ** Warning ** Inside surface heat balance convergence problem continues
  *************  **   ~~~   **   This error occurred 749 total times;
  *************  **   ~~~   **   during Warmup 0 times;
  *************  **   ~~~   **   during Sizing 0 times.
  *************  **   ~~~   **   Max=150.135654 [C]  Min=1.988373E-003 [C]
  *************

Update 3/16/2018: I ran the file with 12 timesteps per hour as suggested in the answer from @Avi. The same errors still occur, and the number of occurrences reported in the error summary actually increased to 1101 times (previously 749 times). What else can I try?

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answered 2018-03-15 05:51:25 -0500

Avi gravatar image

Here is the answer. If it will satisfy you please close the question.

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@Avi, thanks for pointing me to that post, which indicates that increasing the timestep may be a solution. I had not found that one on search.

I'm not closing my question, as I'd still like to know what the error means, why the summary says it did not occur during sizing while the individual warnings say it did occur during sizing, and what, if any, other methods could be used to mitigate the error. The model is ~700 zones, I am running it at 6 timesteps per hour, with only IdealAirHVAC and run time is 4.5 hours, so I'd prefer not to increase to 12 timesteps as the linked post recommends.

Molly Curtz gravatar image Molly Curtz  ( 2018-03-15 10:51:17 -0500 )edit

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Asked: 2018-03-14 16:16:27 -0500

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Last updated: Mar 16 '18