Modelling of secondary air stream in two stage evaporative cooling

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Dear All

I am working on modelling of a two stage evaporative cooling system on EnergyPlus. Supply side air loop consists of an Indirect Evaporative Cooler Research Special and Direct Evaporative Cooler Research Special. I am trying to recirculate some percentage of secondary air stream (exhaust from the indirect heat exchanger) inside the zone and throw out the remaining to ambient. Energy Plus considers secondary air outlet stream as a part of non-parent loop and so it is not running. It will be really great if anybody can guide me on how modelling of secondary air stream can be done on EnergyPlus or any other software?

Thanks