[BLDG-SIM] Modeling 100% OA VAV systems in eQuest (and new EQUEST/DOE-2 versions)

Keir Howell keirh at bluestoneenergy.com
Tue Aug 31 12:28:17 PDT 2004


MessageThank you everyone for your suggestions. I was able to solve the problem with Mr. Hirsch's help. I will have to try out version 3.51. Sounds like some interesting and useful improvements have been made.

Keir Howell
Bluestone Energy Services, Inc.
phone:    781-356-8865
fax:    781-356-8864
  ----- Original Message ----- 
  From: Jeff Hirsch 
  To: BLDG-SIM at gard.com 
  Sent: Tuesday, August 31, 2004 11:18 AM
  Subject: [BLDG-SIM] Modeling 100% OA VAV systems in eQuest (and new EQUEST/DOE-2 versions)


  The problem being asked about arises due to the different uses of the
  alternative methods available in eQUEST freeware (a MS Windows implementation
  of DOE-2.2) to describe both the minimum outside air (OA) damper position
  as well as the minimum flow fraction setting of the VAV boxes in each zone.  

  The min-flow-ratio for a VAVS system (DOE-2 keyword found on the SYSTEM
  properties sheet, fan tab, flow parameters sub tab in the eQUEST details mode
  interface) is the minimum VAV box flow fraction for all boxes supplied by the "parent"
  air handler for the zone; this value can be specified for each individual box or for
  a system and thus "inherited" by all zone boxes supplied by the system. If not given
  a value (min flow fraction control on the mentioned subtab) defaults to the larger of
  the minimum ventilation requirement, the flow required to satisfy the zone peak heating
  load heating, or other available minimum flow specifications (such as cfm/sqft, etc.)
  In dual duct or dual fan dual duct VAV systems the boxes have many more controls
  including separate heat/cool and overall box minimum flow; consult the DOE-2.2
  dictionary (http://doe2.com/download/DOE-22/DOE22Vol2-Dictionary.pdf) or eQUEST
  online help (although this is less complete and not as up to date) for more detail.

  When the outside air fraction is set to 1 this is interpreted as a minimum ventilation
  requirement and thus is found to be the maximum value of the various defaults for
  the VAV box minimum flow value.  If the minimum cfm fraction is specified (on the
  subtab mentioned above) rather than letting it default, the specified value will be used
  for all ZONE VAV boxes in that SYSTEM.

  For example, on the system properties sheet the fan tab and flow parameters sub tab,
  you can place a value for min flow ratio, and that will become the min flow for all VAV
  boxes on the SV-A report  ...
  the hourly OA fraction will then be governed by the fraction of design vs. hourly values
  choice on the system properties sheet outdoor air tab, outside air and economizer subtab.
  If (on the same properties sheet fans /flow subtab) the min flow cfm/ft2 control is set instead,
  you would still get OA=1 all hours because this is one of the values compared to the ventilation
  to choose the maximum needed minimum box flow setting.  (I know the online help is a bit
  dated and poorly worded ... we are trying to get funding to improve it ... but this information
  is all there, just requires a bit of a careful read.)

  By the way, the SV-A, and other DOE-2 reports are now easily examined: the eQUEST
  version 3.51 freeware pre-release posted on http://DOE2.com/eQUEST/ has a new simulation
  results details viewer that allows viewing of multiple .sim files with direct access to reports through
  an index. This viewer can be used to view .sim results file produced by any version of DOE-2.2
  freeware, but is best used with versions 43 and beyond due to fully uniform report headers (in those
  versions) that the viewer uses to locate reports and error messages within a .sim file.

  Version 3.51 of eQUEST has many other improvements to both the simulation engine and interface
  including: a 5-10 times speed increase of project open and compliance simulation times, an first version
  of a BDL error manager to view an error tree to assist in navigation to and fixing of model errors, and new DOE-2
  simulation features that can be found documented (with other post version 40 additions) in Volume 6
  of the DOE-2.2 documentation at
         http://doe2.com/download/DOE-22/DOE22Vol6-NewFeatures.pdf

  This is a pre-release to allow extensive public comment and review (followed by our fixing issues
  identified) prior to the retirement of older versions; this version has been in wide use for some time
  now (starting with version 3.50) and appears to be close to "ready for prime time."

  Happy simulating ...

  ---
  Jeff Hirsch
  James J. Hirsch & Associates
  Building Performance Analysis Software & Consulting
  12185 Presilla Road
  Camarillo, CA 93012-9243 USA
  phone: (805) 553-9000
  fax: (805) 532-2401
  email: Jeff.Hirsch at DOE2.com
  web: http://DOE2.com


    ----- Original Message ----- 
    From: Keir Howell 
    To: BLDG-SIM at gard.com 
    Sent: Monday, August 30, 2004 8:25 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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