How do I model operable windows?

I've been reading about this subject and I know I can do it with a measure. But in which part I will put the opening area?? Because I want OpenStudio finds the flow rate of a window due to natural ventilation. And other thing, not all the windows I have in a zone are operables, there is a problem with that??.

Among many queries, I have the answer about how to model and account for various degrees of opening of a operable window? The operable window can be model in the AirflowNetwork:Multizone:Component:DetailedOpening objective, under the Airflow Network group. In this objective upto maximum four sets of opening factor data for each window can be given to control the opening state of a window. However, It should be remember that the opening factor-1 and opening factor-4 should be 0 and 1 respectively. Opening factor 0 and 1 respectively mean that the window is completely closed and open. In the opening factor 2 and 3 any value greater than 0 and less than 1 can be inserted depending upon the user requirement. For example if the value of opening factor-2 is 0.5 then the model will assume that the window is half open.

Best Sankar