How to calculate the natural ventilation in a "full of holes" zone?

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I'm trying to calculate the thermical behaviour of an exterior zone between two building parts.

As Design Builder can't show results of any external area, I'm trying to close the external zone and full all of its openings with holes.

When i'm reading the results, zone's temperature is above 80ªC as if it was a closed zone (perfectly clear glass effect I guess).

Anybody knows any way to simulate an external zone as its real behaviour? Maybe using vents???