Natural Ventilation: When was the window opened and what was the air flow rate?

I am trying to get a better understanding of the Set EP Airflow component.

I have a single, unconditioned zone (GH attached), with these natural ventilation parameters:


This should mean: “Open the window every time the indoor air temperature is above 26C and the outside air is at least 1C cooler”.

To test this, I wanted to display the window states, but couldn’t find a corresponding output variable. Instead, I tried displaying the air change rates from the result file, but this doesn’t look right:


I then found another output variable which seems to indicate air flow - Zone Ventilation Standard Density Volume - though it does sound like more of a mechanical ventilation metric:

The results seem to indicate that the window was first opened when the preceding time step had indoor/outdoor temperatures of 19.0C and 25.7C respectively.

I guess my questions are:

  1. Is there an output variable that directly describes when the windows are opened or what the airflow rate at the window openings is?

  2. Does E+ take into account that the window cannot open when the space is unoccupied?

  3. How come E+ didn’t “wait” for the temperature to actually exceed 26C before opening the window? Is it the case that the results show the states at the beginning of each time step, so by the end of the time step the temperature was predicted to exceed 26C, thereby triggering a window opening which immediately decreased the temperature? In the definition, I actually set the simulation time step to 1h.

Any help is much appreciated!

nv.gh (582.7 KB)
Weather File