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

[Sheila Sagerer]

MessageBelow I have inserted part of the eQuest help screen for the minimum
OA schedule:

Minimum Outside Air Schedule

Specifies the ratio of minimum outside air flow to Supply Air Flow for each
hour.

If the value in the schedule is a fraction, this specifies the minimum
outside air damper position as a ratio of the design supply air flow rate.
In addition, this enables the economizer.

Since the OA damper position is based on the system design flow, this
definition explains why a schedule specifying 1.00 24/7 converts the VAV to
a constant volume system.  I don't know if this would work but if I was you,
I would first try to set the min OA ratio at 1.00 with the min OA method at
"Fraction of Hourly Flow" and eliminate the OA schedule altogether.  Please
let me know what you find.

Thanks and Good Luck,

Sheila Sagerer
Energy Engineer, LEED AP
Energy Opportunities, Inc
Phone: 717-880-9069
Fax: 717-291-9497





  -----Original Message-----
  From: postman at gard.com [mailto:postman at gard.com]On Behalf Of Joe Hager
  Sent: Monday, August 30, 2004 12:16 PM
  To: BLDG-SIM at gard.com
  Subject: [BLDG-SIM] Modeling 100% OA VAV systems in eQuest


  I recently encountered this same issue.  I found out if I switched the
system type to a Powered Induction Unit that the model would have variable
flow.  Another place to look at is your thermostat type, some systems
default to either proportional or reverse action which effects how VAV boxes
respond to heating and cooling loads.

  Joe Hager
  DMI
  450 Lexington St.
  Newton, MA 02466
  voice: 617-527-1525 ext. 102
  fax: 617-527-6606
    ----- Original Message -----
    From: Keir Howell
    To: BLDG-SIM at gard.com
    Sent: Monday, August 30, 2004 11:25 AM
    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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