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Why no plant loads showing in component load summary - radiant?

asked 2021-03-28 14:07:01 -0500

RCulham gravatar image

updated 2021-03-28 14:07:46 -0500

I built a simple one-zone model with constant flow, floor, low-temperature radiant heating and cooling in OpenStudio Version 2-5-0 with EnergyPlus 8.9. To build the model, I started with the AedgOfficeHVACRadiantDOAS measure. Since there is no ventilation or outdoor air in the model, I deleted the Air Loop.

When I ran the model, the HVAC Sizing Summary report shows the correct zone heating and cooling load. However, though the Component Sizing Summary shows the design hydronic tubing length, it does not report and flow in the chilled water or the hot water loops or the capacity of the chiller or the boiler.

Leaving the floor construction as an internal source construction, I replaced the radiant heating panels, with simple hydronic space heating, attached it to the hydronic plant heating loop and deleted the chilled water loop. Running this simplified simulation, the program then reported the plant heating loop flow and the boiler size.

To double check, I ran the model in OpenStudio App 1.1.0 with EnergyPlus 9.4 and got the same results.

It seems like the radiant panels are not connecting to the plant loops, yet they are graphically shown to be so in the HVAC systems tab. I am wondering why the program is not reporting the capacity of the chiller or the boiler and the corresponding flow rates?

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answered 2021-03-29 19:36:35 -0500

RCulham gravatar image

Thank you Julien for your suggestions as it prompted me to dig further.

I tried AllSurfaces and that did not make a change. I then loaded the OpenStudio idf generated file into EnergyPlus V8.9 IDF Editor and compared my input file with the RadLoTEmpCFloHeatCool EnergyPlus example idf file. I noticed that in the ZoneHVAC:LowTemperatureRadiant:ConstantFlow object, there is an autosize option in the Rated Flow Rate field. This option is not available in the OpenStudio 2.5.0 graphical interface and I did not hard size the flow rate, assuming that the program would do the autosizing. The autosize option is available in OpenStudio App 1.1.0. When I loaded the updated file into the latest version, I did not notice this change and left that field blank which resulted in the same result. I then input a value into the flow field in OpenStudio 2.5.0 and the program generated the results into the Component Sizing Summary.

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Glad you figure it out. Please mark one of the answers as accepted so the thread is mark resolved. It's the gray (becoming green) checkmark below to the "Upvote" and "Downvote" buttons that's next to each answer

Julien Marrec gravatar image Julien Marrec  ( 2021-03-31 03:19:49 -0500 )edit

Glad you figured it out. Please mark one of the answers as accepted so the thread is mark resolved. It's the gray (becoming green) checkmark below to the "Upvote" and "Downvote" buttons that's next to each answer

Julien Marrec gravatar image Julien Marrec  ( 2021-03-31 03:19:53 -0500 )edit
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answered 2021-03-29 02:48:07 -0500

You should double check that you are actually providing the correct combination of Radiant Surface Type with the ConstructionInternalSource object you use.

You place a Low Temp system into a zone. The Low Temp System has a "Radiant Surface Type" field that you should pay close attention to. To debug, you could switch it to AllSurfaces for now.

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Your zone has one or more spaces, and this/these space(s) should end up with at least one surface of the given type that has a ConstructionInternalSource assigned to it. Otherwise, your Low Temp system will not be translated (source in C++ code: ForwardTranslateZoneHVACLowTempRadiantConstFlow.cpp#L75-L85

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Asked: 2021-03-28 14:07:01 -0500

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Last updated: Mar 31