[Equest-users] DOAS MIN-AIR-SCH - schedule values for economizing?

Wed Sep 6 07:52:44 PDT 2017

For reference, I'm answering this in the context of eQuest versions prior to 3.65 build 7174... which I don't think is officially a thing yet but can be found with the label "Release Testing" at http://www.doe2.com/download/eQUEST/.  Word on the street is that this and future builds/versions will feature a proper DOAS system type which could make the rest of this thread inconsequential in the future.

A 100% OA system should have all 1.0's for the MIN-AIR-SCH, independent of whether the system is variable volume.  These scheduled hourly inputs are simply the ratio of OA.

MIN-FLOW-RATIO sets the flow "floor" for variable volume delivery.  It should be exceeded on occasion for a VAV system.

The entry in the doe2 reference manual for MIN-AIR-SCH reads "A value of 0.001 activates the economizer."

I think a value of 0.001 in practice means "zero OA will be delivered, unless determined beneficial for economizer purposes.  There is no minimum OA requirement for this hour."

In summary:  Looks good, Bill!

~Nick

In sorta-related news, when I encounter this I try to steer folks away from adding custom reporting blocks under the "default" Hourly Report.  Adding new blocks alongside the EM1 and FM1 blocks will throw a per-case BDL warning on loading the model.  Those warnings are erroneous in this particular case (doesn't affect the simulation or outputs in any direct sense), but if you get in the habit of ignoring this class of warning you might run into a "boy who cried wolf" situation later when you didn't mean to write over another library component.  I've found this to be a helpful catch in the course of manipulating and applying custom curves.

Better practice is to isolate any new/custom blocks from the default "Hourly Report" with something descriptive that'll help you/others trace what you were looking into down the line:
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Nick Caton, P.E., BEMP
  Senior Energy Engineer
  Regional Energy Engineering Manager
  Energy and Sustainability Services
  Schneider Electric

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From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Bishop, Bill via Equest-users
Sent: Friday, August 18, 2017 2:02 PM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] DOAS MIN-AIR-SCH - schedule values for economizing?

A value of 0.001 in the MIN-AIR-SCH activates an air-side economizer, allowing a unit to provide cooling by varying the volume of outside air.
In a dedicated outdoor air system (DOAS) or other air-side system with 100% outside air, hourly values of the MIN-AIR-SCH should be 1.0.
What about a 100% OA system with variable flow?
I think the hourly values in the MIN-AIR-SCH should still be set to 1.0 for all hours. Hourly reports in my tests show the flowrate increasing above the MIN-FLOW-RATIO during cooling conditions, while the OA is still at 100%.
If I use 0.001 in the MIN-AIR-SCH, the hourly OA% drops way below 100%.

Does this seem right?
Thanks,
~Bill

Custom hourly reports can show the flowrate and OA% of air handlers. This is a typical BDL input for hourly reporting of total system supply air flow rate and OA ratio, in this case for a system "RVU-2":
"RVU-2 Hourly Block" = REPORT-BLOCK
   VARIABLE-TYPE    = "RVU-2"
   VARIABLE-LIST    = ( 17, 39 )
   ..

"Hourly Report" = HOURLY-REPORT
   LIBRARY-ENTRY "Hourly Report"
   REPORT-BLOCK     = ( "EM1 Hourly Report Block", "FM1 Hourly Report Block",
         "RVU-2 Hourly Block" )
   ..

William Bishop, PE, BEMP, BEAP, CEM, LEED AP | Pathfinder Engineers & Architects LLP
Senior Energy Engineer

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134 South Fitzhugh Street                 Rochester, NY 14608

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bbishop at pathfinder-ea.com<mailto:wbishop at pathfinder-ea.com>             www.pathfinder-ea.com<http://www.pathfinder-ea.com/>

[http://png-5.findicons.com/files/icons/977/rrze/720/globe.png]Carbon Fee and Dividend - simple, effective, and market-based.

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