[EnergyPlus_Support] Compact HVAC problems

["josh_miarch" <jeemang@xxxxxxxxx>]

I'm working on a one-zone model that is conditioned using the COMPACT
HVAC VAV objects. I'm having problems controlling the supply air flow. 

I did a run to determine the maximum zone air flow, divided my minimum
required OA flowrate by this number, and then set the result (0.0976)
as the Zone Supply Air Min Flow Fraction in the COMPACT HVAC:ZONE:VAV
object.

The problem I'm having is that the simulation, when heating, fixes the
supply air flowrate to the zone at its minimum, even when there is a
substantial heating load on the zone. As a result, the zone
temperature is often well below (~4°C) its heating setpoint when the
VAV system is running in the heating season. Changing the Zone Supply
Air Min Flow Fraction to a higher value (ie 0.3) fixes this problem in
that it raises the minimum flowrate to an extent that the zone
setpoint can be met, but the system still appears to fix the supply
air flowrate at its minimum.

I'm wondering if anyone can tell me why this system doesn't vary its
supply air flow rate as a VAV system presumably should, or if I'm
understanding something incorrectly. I will shortly upload the model
if anyone would like to take a look
at them.

Many thanks,

Josh



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