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Plant load distribution scheme getting reset from "Uniform" to "Sequential"

asked 2016-02-19 12:58:44 -0500

NickC's avatar

This is another plant equipment operation issue I have been experiencing and was hoping someone could provide an explanation of what is going on here.

I have a pretty standard CHW loop, which has a couple of chillers and three heat exchangers. The heat exchangers go to secondary CHW loops which serve multiple buildings. image description

Both chillers come on and operate together to meet cooling demands. I set the "Load Distribution Scheme" to "Uniform" in OpenStudio and pressed Play. For each loop (CHW and HW) that I've set to "Uniform", I get the following error.

" * Warning * GetPlant/CondenserLoopData: PlantLoop="CHW LOOP (SECONDARY BLDG 11 AND 12)", Invalid choice. * ~~~ * ...Load Distribution Scheme="UNIFORM". * ~~~ * Will default to SequentialLoad. " image description

Looks like E+ is changing the Load Distribution Scheme and the behavior of the chillers looks like a sequential load scheme to me. Is this a bug? Am I doing something wrong here? Thanks! -N

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answered 2016-02-19 13:18:40 -0500

updated 2016-02-19 13:25:21 -0500

It looks like this is a bug in OpenStudio where the available inputs for the OS:PlantLoop field "Load Distribution Scheme" in the OpenStudio input data dictionary file don't match those in the EnergyPlus idd. The OS inputs available are:

A15, \field Load Distribution Scheme
   \type choice
   \key Optimal
   \key Sequential
   \key Uniform

while the EnergyPlus ones are:

A14, \field Load Distribution Scheme
    \type choice
    \key Optimal
    \key SequentialLoad
    \key UniformLoad
    \key UniformPLR
    \key SequentialUniformPLR
    \default SequentialLoad

OpenStudio is just taking the choice "Uniform" and setting that as the idf input (here), but since EnergyPlus isn't expecting that as an available choice, you get the 'Invalid Choice' warning.

@Kyle Benne do you know about this?

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Ah, that makes sense! Good find; looks like a minor bug to me as well. I've been seeing this for a while. If you don't mind, how were you able to determine the mismatch between the OS and E+ inputs?

NickC's avatar NickC  ( 2016-02-19 14:25:36 -0500 )edit

I've seen this for a while too. Knowing that OpenStudio translates the inputs from the osm to idf, and that the .idd files are the ultimate source for the available input information for both programs, I just did a quick search of each idd file (OS here, EnergyPlus here) to see if the input keys matched.

ericringold's avatar ericringold  ( 2016-02-19 14:38:48 -0500 )edit

I couldn't find an existing issue for this, so I've filed one.

ericringold's avatar ericringold  ( 2016-02-19 14:47:58 -0500 )edit

looks like OS is using the keys from EnergyPlusV8-1-0 and the additional Sequential* and Uniform* keys were added in EnergyPlusV8-2-0.

MatthewSteen's avatar MatthewSteen  ( 2016-02-22 15:05:44 -0500 )edit

Just checked the Github request that @Eric Ringold filed (see above); looks like it's "In Progress", thanks @Kyle Benne!

NickC's avatar NickC  ( 2016-03-17 11:48:45 -0500 )edit

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Asked: 2016-02-19 12:58:44 -0500

Seen: 454 times

Last updated: Feb 19 '16