I am simulating (EnergyPlus 6) a 200+ zone building with 116 conditioned zones, with CO2 controlled external air using the IAQP procedure with the needed objects and an external 400 CO2ppm and internal limits from 400 to 1000, apparently it does model the mechanical ventilation but, when I look on the variables output I get CO2 concentrations as low as 90, frequently around 200.

How can I get contaminant concentrations lower than than of the outside air (without an internal CO2 sink) in these occupied conditioned zones? Is there any known issues or recommendations for this air contaminant balance procedure?

Thanks a lot for the attention,

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Leandro M Biondo