[Bldg-sim] eQuest - FCU - how to make it cycle

[Mark Prince]

Yuvaraj,

I'm unaware of any documentation that would support my theory.  This is just my gut feeling.

As for your hourly report, I believe the OA/SA ratio is being reported as 100 CFM divided by whatever the average hourly flow was.  Anytime the average hourly flow is less than 100 CFM it simply reports it as 100%.  The odd thing is that any hour the FCU doesn't cycle it reports the ratio at 90.9%.  ????????  I can not explain this.

Something that does concern me is that it may appear that eQuest is only modeling the 100 cfm of ventilation/exhaust air when the FCU is cycling.  If you want to make sure your results are accurate I would suggest doing the following:

1.)  Serve the zone with the FCU only.  The FCU will take care of cooling/heating load in the zone.

2.)  Find a dummy zone (unconditioned zone) within your energy model and constantly ventilate/exhaust that zone with the 100 CFM.  Be sure to use some wide t-stat ranges so you don't have any unmet heating/cooling load hours and don't waste any energy on reheat.

By separating the FCU from the ventilation, in this way, your energy calculation should be pretty accurate.  Granted, the 100 CFM of ventilation air is probably helping cool your zone some, but I'm guessing from your hourly report that the ventilation is shutting down when the FCU shuts down.  This should be more accurate.

Hope this helps.

Sincerely,



Mark Prince
Affiliated Engineers
5802 Research Park Blvd.
Madison, WI 53719
(608) 441-6668
mprince at aeieng.com

>>> "Yuvaraj Saravanan" <Yuvaraj.Saravanan at arup.com> 9/24/2008 4:07 PM >>>
Mark,
I don't disagree with you. You may be right. But is there any
documentation which says it is how equest reports the supply air
flow-rate?

Other thing is, I am having a continously operating exhasut fan and
outside air fan (24/7) and intermittently operating FCU. Attached is the
hourly report. In this case I have a 100 cfm exhaust and outside air. If
you are right then I dont understand how the ratio of OSA/supply air
flow-rate is reported. Can you give me your insights?

Regards,
Yuvaraj

 

-----Original Message-----
From: Mark Prince [mailto:mprince at aeieng.com] 
Sent: Wednesday, September 24, 2008 11:15 AM
To: Yuvaraj Saravanan; bldg-sim at lists.onebuilding.org;
equest-users-bounces at lists.onebuilding.org 
Subject: Re: [Bldg-sim] eQuest - FCU - how to make it cycle

Yuvaraj,

I believe the "intermittent" mode is the correct way to model this.

When you look at the hourly reports it appears that the fan coil is
varying the airflow rate.  However, I believe eQuest is calculating the
percentage of the hour that the FCU operates and then calculates an
average airflow during that entire hour.  Say the FCU has a constant
volume airflow capacity of 500 CFM, but during one hour it only cycles
on for a third of the hour.  I believe eQuest would then report this
airflow as 166 CFM for that hour in the hourly report.

Hope this helps.

If you disagree please let me know.

Sincerely,

Mark Prince
Affiliated Engineers
5802 Research Park Blvd.
Madison, WI 53719
(608) 441-6668
mprince at aeieng.com 

>>> "Yuvaraj Saravanan" <Yuvaraj.Saravanan at arup.com> 9/24/2008 12:56 PM 
>>> >>>
Hi All,
Does anyone know how to make a FCU cycle ON/OFF based on the zone
thermostat setting? I tried choosing the "Fan on mode" to be
intermittent in the Fan->Flow parameters tab. When I make the fan to be
intermittent, fan is cycling but the supply CFM is no more a constant
volume. It is varying the supply CFM. I observed this in the hourly
report.

ASHRAE standard 90.1 requires the fan to cycle to meet the loads during
unoccupied hours. How everybody model this in eQuest when you have a FCU
system?

Any suggestions is greatly appreciated.

Regards,
Yuvaraj
> ______________________________________________
Yuvaraj Saravanan, PE
Engineer

> Arup
12777 West Jefferson Boulevard Suite 200 Los Angeles CA 90066
> tel:	1 310 578 4400
dir:	1 310 578 4521
> fax:	1 310 577 7011
internal freecall: x20521
yuvaraj.saravanan at arup.com 
> www.arup.com 
> 
> 
____________________________________________________________
Electronic mail messages entering and leaving Arup  business systems are
scanned for acceptability of content and viruses