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Ground heat transfer data and similar detailed input in Open Studio

asked 2015-03-23 05:07:38 -0600

Jacob Lindblom gravatar image

updated 2015-07-11 17:14:25 -0600

I am learning OpenStudio and EnergyPlus and are practising by creating a building model in OpenStudio and the SketchUp application.

To set input data regarding ground heat transfer in my model, I first thought that I should export an idf-file from OpenStudio, set the input in the idf-file (Detailed Ground Heat Transfer section for example), and then reimport the idf-file to OpenStudio to run the simulation and/or continue to work on my model. However I understand that I lose parts of my model during idf export-import.

I understand that I could write a measure using Ruby that could allow me to insert the heat transfer data from OpenStudio. This would however require some work.

I could of course finalize my modelling in OpenStudio, export an idf-file, add further details in the idf-file and run the simulation using Energy Plus-EPLaunch only. The added idf-detailes would then need to be re-entered if I would go back to OpenStudio and /or the SketchUp application for modification.

Are there any better options if I want to set detailed Energy plus input data, not handled byOpenStudio, and still be able to continue modelling and simulation in OpenStudio?

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answered 2015-03-24 23:43:13 -0600

updated 2015-04-06 14:46:27 -0600

You are entirely correct on the consequences of moving out of OpenStudio into modifying IDF files directly. The use of EnergyPlus measures is our current solution to this issue. You might try making an EnergyPlus measure, the example shown in the measure writing guide has an example of adding IDF text directly to your file.

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I should also comment that we want to add access to the detailed ground simulation methodology in EnergyPlus directly from the OpenStudio GUI tools at some point, we just have not had the resources to do this yet.

macumber gravatar image macumber  ( 2015-03-24 23:44:16 -0600 )edit

Good to know! I was having a hard time figuring out that was happening with one of my models because the peak cooling loads were not making any sense to me. It was not until I got saw the Zone sizing and Summary Report (is not one of the default reports in energyplus) that I saw that I was having a 30% heat loss through the floor slab.

Carlos Vazquez gravatar image Carlos Vazquez  ( 2015-04-03 09:56:44 -0600 )edit
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answered 2015-03-27 14:30:36 -0600

Jacob Lindblom gravatar image

updated 2015-04-24 01:12:16 -0600

Thanks a lot for the answer. I have now tried to write my own measure. During this struggle I was inspired by an existing EnergyPlus measure from the BCL-web (AEDG K12 - SlabAndBasement) which includes "a call" to a short idf-file to include new objects. So I wrote a measure with the following code in the measure run section:

 dummyIdfPath  = OpenStudio::Path.new("#{File.dirname(__FILE__)}/resources/dummy.idf")
 dummyIdf = OpenStudio::Workspace::load(dummyIdfPath).get
 workspace.addObjects(dummyIdf.objects)

Then I can use the e+ IDFEditor to create dummy-files containing whatever objects not covered by OpenStudio and put them in a folder named resources in the measure folder. Preliminary tests indicates that it works. The test objects anyway turns up in the ...run\4-EnergyPlusPreProcess-0-folder.

Amendment: Later I have concluded that the method above is a useful method to add things to the idf before e+ receives it. However does OpenStudio run the ExpandObjects before running the Measure and it is during the ExpandObjects run that the Basement related objects must be present in the idf to have desired impact. My final, slightly simplified, solution to my problem is as follows:

  • Write a short idf-file using IDF-Editor only containing the necessary Basement objects in the Detailed Ground Heat Transfer group
  • Modify this file by removing "GroundHeatTranfer:Basement:" from all component names
  • Run the file in Basement using EP-Launch-Utilities
  • Take the temperature results from the Basement run - Calculate one representative temperature per month that, applied on both underground walls and basement floor, should result in the same heat transmission (considering areas and temperature differences)
  • Insert these temperatures in a short idf file only containing the Site:GroundTemperature:BuildingSurface object
  • Add this file to the main model using the method in my previous answer

Now I can continue work in the OpenStudio model and run simulations without bothering to much about the basement heat transfer as long as I do not modify parameters related to it. I realise that this could have been done more elegant, but this is good enough for my purposes anyway.

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I've created a short idf file only containing the Site:GroundTemperature:BuildingSurface object, but I do not understand how did you put this file in the main model. Are you talking about the EnergyPlus model or the Openstudio model?

Gjko gravatar image Gjko  ( 2017-02-24 12:40:11 -0600 )edit

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Asked: 2015-03-23 05:07:38 -0600

Seen: 822 times

Last updated: Apr 24 '15