i trying to design a cross-ventilation solution for an open-air structure. many passive-solar design manuals for example (Sun, Wind & Light) assume a difference between outside and inside temperature of around 3 degrees farenheight. how am i supposed to assume such a difference while i am still designing a building like an open-air structure. i know the heat-gain in w/m2...but i dont know how to establish a true difference. ...can someone offer me some guidance? thanks