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Learn the EnergyPlus Data Format (Part 2)

April 20, 2017

Last time, we mentioned a lot about the .idd file. What is it? The idd file is the EnergyPlus input data dictionary, which sets the rules for the data. You can find this file under the EnergyPlus installation folder. Its name is "Energy+.idd". You can view this file by open it in a text editor such as NotePad++ or Sublime Text. 

Material,
    \memo Regular materials described with full set of thermal properties
    \min-fields 6
  A1 , \field Name
       \required-field
       \type alpha
       \reference MaterialName
  A2 , \field Roughness
       \required-field
       \type choice
       \key VeryRough
       \key Rough
       \key MediumRough
       \key MediumSmooth
       \key Smooth
       \key VerySmooth
  N1 , \field Thickness
       \required-field
       \units m
       \type real
       \minimum> 0
       \maximum 3.0
       \ip-units in
  N2 , \field Conductivity
       \required-field
       \units W/m-K
       \type real
       \minimum> 0
  N3 , \field Density
       \required-field
       \units kg/m3
       \type real
       \minimum> 0
  N4 , \field Specific Heat
       \required-field
       \units J/kg-K
       \type real
       \minimum 100
  N5 , \field Thermal Absorptance
       \type real
       \minimum> 0
       \default .9
       \maximum 0.99999
  N6 , \field Solar Absorptance
       \type real
       \default .7
       \minimum 0
       \maximum 1
  N7 ; \field Visible Absorptance
       \type real
       \minimum 0
       \default .7
       \maximum 1

 

This is the Material object in EnergyPlus. Read through this text, the first thing you will see is the "\memo" and "\min-fields" under "Material". These are called the Object-level comments. "\memo" describes the object, what is it and what does it do, and "\min-fields" defines the minimum number of fields that should be included in this object. In this example, it is 6, which means the first six fields are the required fields. Let's dig in deeper!

 

The text below the Object-level comments is EnergyPlus fields and Field-level comments. The fields are labeled with either "A" or "N". "A" stands for alphanumeric string, which means it is non-numeric value. Obviously, "N" is numeric. The Field-level comments also start with "\". For "A1", we found a "\field", a "\required-field", a "\type" and a "\reference"

A1 , \field Name
       \required-field
       \type alpha
       \reference MaterialName

  • The "\field" is the most common comment for fields. It simply shows the name of the field. So the name of "A1" is "Name".

  • The "\required-field" comment labels that the "A1" is a must have field in this object. It would cause failure if modeler did not fill in something in "A1" field.

  • The "\type" comment indicates the type of data. Currently include:

    • ​Integer (e.g. 1,2,3,4,5, ...)

    • Real (e.g. 3.1415926, 5.678, ...)

    • Alpha (e.g. Concrete, Fibre glass insulation, ...)

    • Choice, choose a string from a designated list (e.g VeryRought/Rough/MediumRought/MediumSmooth/Smooth)

    • Object-list: indicates the data of this field has to link to a list of EnergyPlus objects defined elsewhere.

    • External-list: Data is coming from external source, this is typically see in Output:Variable or Output:Meter objects

    • Node: HVAC node.

  • The "\reference" shows this field can be referenced as the MasterialName, which the objects defined elsewhere can reference on. You can guess the "object defined elsewhere" must be a construction related object such as the "Construction".

This is just one example, there are many other Object-level comments, and Field-level comments and the list can be found on the top of the IDD comments sections (those lines starts with a !). Let's find more next time!!

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