Hi @chris , hi all,

I have some thoughts about the component setEPNatVent and its relationship with EnergyPlus.

For stack driven ventilation, EP takes into account the input called “height difference”

“https://bigladdersoftware.com/epx/docs/8-0/input-output-reference/page-018.html#field-height-difference” which reffers to the difference between the midpoint of the lower opening and the Neutral Pressure Level. On top of that, according to 2009 ASHRAE Handbook of fundamentals chapt. 16, equation 38 (from which the EP formula is based on), when one deals with only one opening, the NPL is the midpoint of that opening and the height difference should be half of that opening height.

The problem is that when I run a simulation with one window on one side using the setEPNatVent component, and when I check the IDF file, the input for height Difference is the total window height. And this is not corrected by EP because the result airflow volume from my simulation corresponds to the theoritical calculation using the EP formula (https://bigladdersoftware.com/epx/docs/8-0/input-output-reference/page-018.html#field-height-difference).

In this situation, shouldn’t honeybee write in the IDF file half of the total window height for the height difference input ?

Also, is there any particular reason why honeybee sets the discharge coefficient with fixed values (stackDischargeCoeff_ input) instead of the formula used in EP when user sets it to autocalculate ?

Again, according to ASHRAE, this coefficient should be set to 0.65 when the openings away from each other and the air flow is unidirectional, and should be C = 0.40 +0.0045(Tint - Tout) when there is one window and mixing can occur.

My guess is that all what I mentioned above is actually taken into account in the stack discharge coefficient of 0.25 that you suggest to use when there is only one window… but I’m not sure

Cheers !