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

Peter Alspach peter.alspach at arup.com
Tue Feb 21 09:22:43 PST 2006


Renee - check your system sizing variable. I believe it defaults to 1.15, which explains your 15% oversizing. If you set your airflow and set this to 1.00 then you should be set.

Pete

-----Original Message-----
From: BLDG-SIM at GARD.COM [mailto:BLDG-SIM at GARD.COM] On Behalf Of Renee J. Azerbegi
Sent: Saturday, February 18, 2006 2:44 PM
To: BLDG-SIM at GARD.COM
Cc: 'Linda Morrison'
Subject: [BLDG-SIM] Displacement ventilation and airflow modeling in eQuest

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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