IES-VE User Forum

Does someone has an idea which controller is responsible to maintain minimum OA supply during system occupied hours in ASHRAE 90.1 PRM Baseline System 7 as I only see airflow controllers that are driven by sensed temperature (circled in orange)? I get negative airflow @ node 881 when running Apache simulation. This is probably due to the fact that initially the system is not operating since it does not need to heat up any space but exhaust is always on during system occupied hours...

On another note, how are VAVs able to maintain 30% turndown airflow if the controllers circled in orange have on/off control activated by default?

There's 30% (hey, just like the VAV trurndown! setting) chance that someone will answer this as this forum is pretty much a graveyard of unanswered topics, but I am a dreamer!

Tough one, heh?

Not sure I understand your question, but if you are trying to set minimum Outside air airflow, I do this at the damper to the left of the supply fan graphic. (There's probably a way to do this from within the System Parameters window, but I'm still warming up to that thing personally)
As for maintaining minimum 30% flow, I don't trust the "default" controller settings for much of anything, much less that.
I would set the controller to "On Continuously" and check the box in the System Parameters window on the "Room Ventilation & Exhaust" tab for "Outdoor air percentage requirement (min % of air to room)" and enter 30% in the input field.

Sorry for the late response, I'm sure it's too late for the OP, but maybe my response will help someone else with a similar issue. (Or confuse them more, which is entirely possible)

Tom