[BLDG-SIM] Modeling 100% OA VAV systems in eQuest

[Mike Tillou]

Keir,
I tried to reproduce your error but cannot get eQuest to simulate a VAV
with 100% OA as a constant volume system.  Without seeing your input
file I suggest the following:
 
1. Check the version of eQuest you are using.  I used version 3.44 build
2930 and had no problems.  Version 3.5 is also available but I haven't
spent much time with it yet.
 
2. I assume you have checked the hourly reports to verify the constant
airflow.  If not run hourly reports to verify supply airflow rate and %
OA.
 
3. Check to be sure you're not using a minimum OA schedule.
 
4. Verify that at the zone level you have reset all values for OA
calculations to zero
 
5. If you have manually entered a design CFM, it may not be large enough
to meet the load and as a result the VAV is not modulating.  I suggest
reseting the Design CFM to default and letting eQuest size the air-flow
rate.  Another way to check this is to look at the SS-O reports.  If
zone temp setpoint is not being met you will have a wide distribution of
hours at different temp ranges.  This could happen if you have a large
internal cooling load that isn't very sensitive to fluctuations in
outdoor temperature.  
 
6.  Try changing the minimum outside air ratio to 0.25 or some value
other than 1.0, does the hourly supply air flow change?  It shouldn't
change because supply air flow is dependent on the loads at the zone
level.  
 
Those are some of the things I would try to help understand what is
going on.  It may be that the model is doing what it is supposed to.  
 
I hope this helps.
 
Mike
 
 
Michael Tillou, PE
etc Group, Inc.
PO Box 7, Williamstown, MA 01267
ph. (413) 458-9870 
  

-----Original Message-----
From: postman at gard.com [mailto:postman at gard.com] On Behalf Of Keir
Howell
Sent: Monday, August 30, 2004 11:26 AM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] Modeling 100% OA VAV systems in eQuest


Hello. Whenever I try to model a VAV system with 100% OA in eQuest, I
end up with a constant volume system. It seems to be multiplying the
Minimum OA Ratio (which I have set at 1.00) by the design air flow,
rather than the hourly air flow, even though I have set the Minimum OA
Method to "Fraction of Hourly Flow". As far as I know, I have not set
any other variables (such as zonal settings) that might override the
system settings. Please help. Thanks,
 
Keir Howell
Bluestone Energy Services, Inc.
phone:    781-356-8865
fax:    781-356-8864


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