Calculating airflow from window opening to assess natural ventilation



Dear all,

I am trying to assess window-based natural ventilation, so is there a method to calculate airflow from an opened window (a certain opening ratio or area, 50%)?

Also, I want to find how much air is needed to enter a space to maintain CO2 level under 1000 ppm, is there a way to measure indoor CO2 concentration? Or setting natural ventilation based on CO2 level rather than temperature?

Thanks for your help in advance.