RMC
Actually I took the infos from the NG Training documentation.
During normal operation, two electrical recirculation fans draw air from the passenger compartment and the equipment cooling system through filters. The recirculation air is delivered to the mix manifold through check valves. The recirculation fans and check valves are identical and interchangeable. The recirculation rate
is approximately 47 m3 per minute. No recirculated air goes into the flight
compartment.
The air in the airplane is changed every three minutes.
Like I also remember, It is mandantory by law to have an independent airflow to the cockpit.
rgds