I posted this in a reply to another thread, but didn't get any responses. This is really holding up my use of Revit. Can you please help?
As shown in the attached word doc, a new supply air system is created for each VAV box, which is different than (not nested beneath) the AHU's system. Therefore, when I try to get the external static pressure drop of the actual system (i.e. from the AHU's supply fan, through the index run's diffuser, including VAV box losses - what I need to size the system's supply fan) I'm only getting the static pressure drop of each "Revit system" (i.e. from the AHU's supply fan to the inlet of all assigned VAV boxes OR, from the VAV outlet through that zone's index run diffuser). Additionally system inspector only lets you inspect these "Revit systems", not the whole system.
As an example, look at the first picture in the attached word doc, and you'll see that all my supply diffusers have a pressure drop of 0.09 in-wg, and my VAV boxes each have a pressure drop of 0.25 in-wg. The result is a calculated required static pressure at my VAV boxes, and at my AHU supply fan (0.43 in-wg, circled in red). Now look at the second picture. I've changed the pressure drop of all supply diffusers to 0.25 in-wg. The required static pressures at VAV box outlets increases, however the static pressure for the AHU fan module remains 0.43 in-wg. This 0.43 should have increased, with the increase in pressure drop of the supply diffusers.
It seems to me that there should be a system level (comprised of all supply components that are connected to a particular AHU) and zone levels, actually nested beneath the system (comprised of each VAV box and their downstream supply components). Can you please inform me of a better way to organize a VAV system so that I can get the actual external static pressure drop needed to size the AHU supply fan? Or, how are you getting around this limitation?
Thank you,
Pete
Edited by: peterworley on Feb 5, 2010 7:10 AM
