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Curves for ChillerHeater:Absorption:DirectFired Component in EnergyPlus

asked 2016-01-20 14:17:59 -0500

updated 2016-01-20 16:15:39 -0500

Hi All,

I have an gas powered absorption chiller providing both chilled water and hot water in my model. I modelled this using ChillerHeater:Absorption:DirectFired. According to the Input-Output reference guide and the the engineering reference guide, the following curves need to biquadratic/bilinear.

"Cooling Capacity Function of Temperature Curve Name" "Fuel Input to Cooling Output Ratio Function of Temperature Curve Name" "Electric Input to Cooling Output Ratio Function of Temperature Curve Name"

However, EnergyPlus does not let me select these curve types presently. I am not sure if this component is functioning as desired. Has anyone else run into the same problem with this component? Any guidance over this issue would be much appreciated.

Thank you,


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What do you mean by "EnergyPlus does not let me select these curve types"? Is it because the cells are shown in orange in IDF-Editor, or because the simulation fails if you try to use your curves?

Aaron Boranian gravatar image Aaron Boranian  ( 2016-01-20 16:15:03 -0500 )edit

I mean that EnergyPlus does not show the curve types (BiQuadratic) in the dropdown for these fields. It is shown in orange color in the image as I typed in the BiQuadratic curve names in these fields. The simulation runs through even if these fields are orange in the IDF editor but I just wanted to make sure that I understand the functioning of this component.

rsunnam gravatar image rsunnam  ( 2016-01-20 16:23:51 -0500 )edit

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answered 2016-01-20 17:16:03 -0500

I can see why the orange color for the input cells in IDF-Editor are giving you alarm. Normally, this indicates an input error. You are correct in stating that the EnergyPlus documentation makes it seem like these performance curves for chiller heater objects must be biquadratic or bilinear. The ultimate resource for proper input fields is ALWAYS the Energy+.idd file. If there is ever an inconsistency between the Input / Output Reference and the IDD file, the IDD file is always correct.

If you look at these performance curve input fields for the ChillerHeater:Absorption:DirectFired object in the IDD file, you'll notice that there are several options to choose from via an object-list:

  • LinearCurves (collection of all Curve:Linear objects in the model)
  • QuadraticCurves (collection of all Curve:Quadratic objects in the model)
  • CubicCurves (collection of all Curve:Cubic objects in the model)
  • QuarticCurves (collection of all Curve:Quartic objects in the model)
  • ExponentCurves (collection of all Curve:Exponent objects in the model)
  • UniVariateTables (collection of all Table:OneIndependentVariable and Table:MultiVariableLookup objects in the model)

For your case, trying to select a Biquadratic curve for this field doesn't match with what the IDD has as available options, so the cell is orange in IDF-Editor. This is why your quadratic curve is not orange, since quadratic curves are available options according to the IDD file.

If your file still runs and doesn't crash, then EnergyPlus SHOULD be using the performance curve correctly. To be sure, you can track the performance curve output value from the *.RDD file that gets generated after each EnergyPlus run. It should be

 HVAC,Average,Performance Curve Output Value []
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See this related issue.

Eric Ringold gravatar image Eric Ringold  ( 2016-01-20 18:52:17 -0500 )edit

Thank you @Aaron Boranian for your explanation and @Eric Ringold for pointing out to this resource. It is very helpful to know this to be a known issue for me to verify my results.



rsunnam gravatar image rsunnam  ( 2016-01-20 19:59:40 -0500 )edit

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Asked: 2016-01-20 14:17:59 -0500

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Last updated: Jan 20 '16