Hello, We took look at the model, and found some things that will get the model to compute without an error message. First, you can change the attribute "Use Extended CAV?", found in the transient calculation options to False. The model will complete without an error. You can find more on Extended CAV in the air valve TechNote, found here: If you need to use Extended CAV, there is a step you can do that will allow the transient solver to use more trial to find a solution. Details on this can be found in the following link: communities.bentley.com/.../11859.changing-transient-accuracy-and-max-trials-solution-500000075659.aspx Basically, you would add the phrase USE_SS_EPS_TRIALS_AND_ACCURACY to the Notes field in the transient calculation options. This will allow you to use the same number of trials that are used in the Steady State/EPS solver. As with the other possible solution, the model will complete. There are a few other things you may want to look at in the model. First, the air flow curves may need to be adjusted. Typically, you would not combine the positive and negative air flow into one curve. It would be better to have these split into separate curves. In addition, you may want to review the discharge coefficients entered for the TCVs, as the values seem very high and are not resulting in much headloss. Basically, you would do a sensative analysis, trying different values (such as 10,000), then computing the model. If there is a large difference in the pressure envelope in the transient results, you may want to review the values entered for the TCV. If all of this is correct, the results are telling you that more protection may be needed in this system when the valve is closed so quickly. You can try putting in air valves closer to the valve that is shutting down, or try other devices to see if they offer better protection. Please let us know if you have any other questions. Regards, Scott Kampa Bentley Technical Support
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