[Equest-users] FCU with outside air fan

Aulbach, John jaulbach at nexant.com
Tue Sep 23 09:04:09 PDT 2008


Try a 4-pipe induction unit. I believe that can have primary and
secondary coils. Ignore that you can't model the fan coil fan. It is
insignificant. 

I used to do this to model a guest room fan coil with supply and exhaust
air to the guest room. Don't do every room. Do building facing
directions.

John R. Aulbach, PE, CEM
Project Manager
Nexant, Inc.
701 West Kimberly Ave., Suite 245
Placentia, CA 92870-6342 USA
Phone: 714-524-4402
Fax: 714-524-4407
email: jaulbach at nexant.com
 


-----Original Message-----
From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Yuvaraj
Saravanan
Sent: Monday, September 22, 2008 9:05 PM
To: bldg-sim at lists.onebuilding.org; equest-users at lists.onebuilding.org
Subject: [Equest-users] FCU with outside air fan

Hi All,
I am trying to model a residential unit served by a Fan coil unit (FCU).
It has a separate outside air fan and exhaust fan operating 24/7. The
fan coil unit is available to operate for all hours but should operate
intermittently depending on the room load.

I tried modeling this by selecting a 4-pipe FCU and specified the
exhaust and outside air at the thermal zone level. I made the FCU to
operate intermittently by making the "Fan on mode" to be intermittent.
By doing this, what I observed in the hourly report was:
1. FCU unit cycles intermittently as intended.
2. Exhaust fan operates continuously (24/7) (with the specified cfm) as
intended.
3. However, the outside air cycles per the FCU. 
*If the FCU is off, then OA cfm is zero
*If FCU supply air cfm < the OSA cfm specified at the zone level, then
hourly OSA cfm matches the FCU supply air cfm *If FCU supply air cfm >
the OSA cfm specified at the zone level, then hourly OSA cfm matches the
cfm specified at the zone level.

As mentioned before, I want my outside air to operate continuously with
constant flow-rate. Can anyone suggest me a way to model this system?

Thanks in advance for your help!
Regards,
Yuvaraj
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