[BLDG-SIM] Displacement ventilation and airflow modeling in eQuest

Renee J. Azerbegi renee at ambient-e.com
Sat Feb 18 14:44:16 PST 2006


Greetings,

For a middle school in Colorado, I'm modeling a constant volume displacement
ventilation system and comparing this to a conventional variable air volume
with reheat overhead system.

I cannot seem to set an exact total AHU airflow rate that has been
calculated by the mechanical design engineer. When I do this, the eQuest
program adds about 15% of airflow to the AHU airflow rate I specified. I
specified at the zone and at the system level and each time, it increases
the total airflow rate, even when I remove the exhaust airflow. Has anyone
had this happen to them before? I did set the altitude to zero since that is
what you are supposed to do if you want to put in exact airflow rates.

The number of hours outside the throttling range for the displacement system
is very high since the temperature entering the space is a constant 68 F and
the setpoint for the room is 70 F. The baseboard sizes have been entered and
are maximized for the exterior wall. If I change the plenum height to
anything above six feet being plenum, then part of my windows will be in the
plenum which eQuest has a problem with. I have put in all the possible
mechanical design parameters of the two types of systems into eQuest, except
the fact that one is entering in overhead and one system is entering into
the space at the floor level. I'm not sure if it is reasonable to assume
that it is modeled correctly with many unmet hours of heating. But perhaps
it is due to the limitations of modeling this type of system? Has anyone
effectively estimated the performance of displacement ventilation in eQuest
such that it is as designed without many unmet heating hours?

Also, just for some background, there is no cooling - cooling is provided
only by an economizer cycle as they have summers off and the school is in
the mountains.

Any suggestions to either of these issues would be greatly appreciated!

Thank you,

Renée




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