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Why is Site:WaterMainsTemperature Correlation from Weather File locked on one temperature for all times and locations?

asked 2021-11-11 15:59:59 -0600

matt gravatar image

I'm trying to use a Site:WaterMainsTemperature object to get a Correlation Site Water Mains Temperature output variable. Because I want my model to be flexible across sites, I set the Calculation field to CorrelationFromWeatherFile. When I run a test, however, I see that the output is locked at 3.33 degC. This value appears for every timestep and for disparate locations; Phoenix and Chicago TMY3 files return the same value, 3.33 degC. I even tried Chicago TMY2 in case it was some sort of epw file version issue, but still it returned 3.33 degC.

If I switch to the Correlation method and throw in some input values, I see the water mains temperature vary as expected, with a different temperature each day and different temperatures between sites.

The HTML table gives me a possible hint; the numbers it apparently calculates from the weather file are very small and again are the same value for Phoenix and Chicago. Phoenix HTML Table output

I haven't found any other questions about this except for this question regarding OpenStudio not having Correlation from Weather, but I'm working directly with EnergyPlus IDF editor, not OpenStudio.

Has anyone else had this issue? Is it a bug or am I just missing an object input somewhere to make this work correctly?

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@nigusse I think you added this to EnergyPlus. Any idea?

shorowit gravatar image shorowit  ( 2021-11-11 17:26:40 -0600 )edit

I've had this issue, too! No way to tell e+ to use the following object to inform the cold water supply temperature at source-side inlet node for water heater within plant loop: Site:WaterMainsTemperature, CorrelationFromWeatherFile; Within the WaterHeater:Stratified section (9.5.0), the following is indicated: Field: Cold Water Supply Temperature Schedule Name ... If blank, water temperatures are calculated as above. This field is for stand-alone operation only. If there are node connections, this field is not used. I can find no indication of how to assign to source-side node.

RMurray gravatar image RMurray  ( 2021-11-14 21:09:34 -0600 )edit

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answered 2021-11-15 09:36:29 -0600

updated 2021-11-15 09:36:51 -0600

I am able to reproduce the bug and have filed an EnergyPlus bug report. In the meantime, you'll have to use the Correlation calculation method and obtain the two input parameters yourself from the weather file or stat file.

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Thanks @shorowit for looking into it and filing that report. I'll keep an eye out for the fix and use Correlation inputs in the meantime.

matt gravatar image matt  ( 2021-11-15 10:00:26 -0600 )edit
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answered 2021-11-17 11:44:51 -0600

RMurray gravatar image

Demonstration of "frozen" Site:MainsWaterTemperature values against the backdrop of outdoor DBT. This despite including the following object: Site:MainsWaterTemperature, CorrelationFromWeatherFile;

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Asked: 2021-11-11 15:59:59 -0600

Seen: 211 times

Last updated: Nov 17