I am trying to model natural ventilation by using simplified method i.e. ZoneVentilation:WindandStackOpenArea object but have few queries regarding this. This object has fields of Effective angle and Height difference. The effective angle is the angle in degrees counting from the North clockwise to the opening outward normal. The value must be between 0 and 360, so if the window is on North side then this is equal to 0 (please correct me if I am wrong).
My first question is, what if the model has two windows (e.g. one on North side and one on South or east side), what will be the effective angle in that case?
My second question is regarding Height difference, it is written in the Input output reference guide that estimation of height difference in difficult for natural ventilated buildings (see chapter 16 ASHRAE Handbook of Fundamentals 2009, which may provide guidance). In HOF 2009, it is written that If one window or door represents a large fraction (approximately 90%) of the total opening area in the envelope, then the NPL (Neutral Pressure Level) is at the mid-height of that aperture, and , HNPL (Height of Neutral pressure level) equals one-half the height of the aperture.
This means for one large window this field will be the mid point of that window, right? Again, what if the model has two windows on same wall surface (lower and upper windows), then how we can calculate this height? Also, what if the model has two opposite windows (one of North and one on South side)?
If it is difficult to calculate then can we conclud