Hello All,

I?ve come across an unexpected result and thought I?d share? maybe someone
here can shed some light. I am modeling a VAV air handler with supply and *
relief* fans.

When I try to enter the design flow of the relief fan (RETURN-FLOW
keyword), which is about 90% of the design supply flow, the model forces
outside air to be at least 10% (the leftover from 90%) * [supply flow] for
all hours that the fans are running, including night cycle hours when I
force outside air to 0 using the MIN-AIR-SCH keyword. I believe this
behavior is intended for return fans, and I?ve indicated that I want to
model a relief fan using the RETURN-FAN-LOC keyword. The increased outside
air, affecting all of the night cycle hours and sometimes interfering with
DCV control, has a significant effect on simulation results.

For the project I?m working on, I?ve restored the RETURN-FLOW keyword to
default, since I don?t think the effect on the results will be significant.
But I?m curious whether anyone else has noticed this, or has any thoughts
on the issue?

Regards,

Mike

Mike Karpman