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Unexpected Warning (Max iterations)

asked 2015-11-02 15:44:12 -0500's avatar

updated 2015-11-03 05:23:18 -0500

I was trying to simulate in E+ two Window AC Units in the same Thermal Zone when I got this Warning in my Error File.

" * Warning * ZoneHVAC:WindowAirConditioner="WINDAC2" -- Exceeded max iterations while adjusting compressor sensible runtime to meet the zone load within the cooling convergence tolerance. * ~~~ * Iterations=50 During Warmup, Environment=SAO_PAULO/CONGONHAS ANN CLG .4% CONDNS DB=>MWB, at Simulation time=02/21 08:00 - 08:10"

What does that mean? When I simulated with only one Window AC it did not appear. I already tried changing the Convergence Limit to 70, but the error keeps appearing, so I think that's not the problem...

Can anyone help me?

Here is the link:IDF with only 1 AC and here is the link:IDF with 2 ACs

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answered 2015-11-03 05:43:18 -0500

Archmage's avatar

Try to relax the value in the input field called Cooling Convergence Tolerance in the ZoneHVAC:WindowAirConditioner object. The value of 0.001 is sometimes too small.

Note that when there are multiple ZoneHVAC units in the same zone they are staged so that the second window AC will pick up the load remaining after the first unit tries to meet the zone's cooling load. They won't both run together at the same loading. Because both units are autosized here, it is likely that the first unit will be able to meet all the load and the second one is not going to do much. Modeling two units makes more sense if the sizes are fixed at input. Even if the zone really does have two units in the actual building, it is common to model as one larger unit.

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Hi @Archmage! That was useful :) So...if I don't autosize anything inside my HVAC system, I can make them work together? Or would I need to use EMS?

I tried sizing everything (besides Outdoor Air Flow) and I keep getting that error...'s avatar  ( 2015-11-03 10:39:23 -0500 )edit

You can get them to work at the same time but they will always be staged so that the first one runs first and the second one picks up the remaining load. Even with EMS I can't think of way around this. The multiple ZoneHVAC capability is intended for different types of equipment, not two of the same.

Archmage's avatar Archmage  ( 2015-11-03 15:14:38 -0500 )edit

@Archmage, sorry for disturbing you again, but do you know why I keep getting the error even after I relaxed the Convergence Tolerance and sized the equipments?'s avatar  ( 2015-11-03 16:24:33 -0500 )edit

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Asked: 2015-11-02 15:44:12 -0500

Seen: 283 times

Last updated: Nov 03 '15