On a venting dehumidifier like an UA 150XT, how does one control the amount of intake air? How can you tell what the actual amount of airflow is? On an ERV it's easy since all of the air flow from the fans comes from outside, but I'm a bit confused as to how one would regulate/meter/adjust flow on a ventilating dehumidifier.

Also, would the dehumidifier run every time there was a call for ventilation? What if outside air was "dry enough" already?