<div class="gmail_quote">Dear esp-r users, I'm modeling an atrium with a closed glass roof. The atrium has nearly 16m height and it only connects to the outside through 3 cracks on the roof. I divided the atrium into 5 vertical zones, and adjacent vertical bypass zones. They are connected to each other through fictitious faces. Common orifice components connect zone nodes to each other vertically, and door component connects zone nodes to bypass nodes horizontally. The attached image shows the Air Flow Network in my model more clearly. I supposed that esp-r includes the stack effect whenever delta height between the nodes and the component is not zero. So I expected to have a stack pressure in the vertical connections. But when I check the results the stack pressure in the connections are zero! I'm also curious how esp-r consider the stack effects and the gravity? The components dP are set manually and there is no "g" in the equations? Where I can find the PSTACK equations that is used to calculate DP: DP=PRES(IDPS)-PRES(IDNE)+PSTACK(ICNN). Thanks in advance. Mostapha Sadeghipour </div>