Is there a way to extract thermal mass from an energyplus model?

edit

To do it programmatically, you could either use OpenStudio and Ruby or EnergyPlus and Python.

OpenStudio and Ruby

Import the IDF to OpenStudio and as @Luis Lara suggested run a Ruby script (or formal OpenStudio Measure) on the OpenStudio model.

EnergyPlus and Python

Here's a lightly tested Python script (using eppy). Depending on your model, you may want to add filters (e.g. Construction:InternalSource, Material:NoMass, etc.).

import os
from eppy.modeleditor import IDF

idd_dir = r'C:\EnergyPlusV9-1-0'
idd_file = r'Energy+.idd'
idd_path = os.path.join(idd_dir, idd_file)

idf_dir = r'C:\WORK\18151 DEN Level 4\18151-Baseline\run'
idf_file = r'in.idf'
idf_path = os.path.join(idf_dir, idf_file)

IDF.setiddname(idd_path)

idf = IDF(idf_path)

total_heat_capacity = 0

surfaces = idf.idfobjects['BuildingSurface:Detailed'.upper()] 

# loop through the surfaces to calculate heat capacity
for surface in surfaces:

    construction_heat_capacity = 0

    construction = idf.getobject('CONSTRUCTION', surface.Construction_Name)

    # get the field names, which in eppy is a list of 
    # ['key', 'Name', 'Outside_Layer', 'Layer_2', ... 'Layer_10']
    construction_field_names = construction.fieldnames

    # loop through the construction's field names (layers), 
    # skipping first and second (key and Name)
    for field_name in construction_field_names[2:]:

        # get the material object from the layer
        attribute = field_name
        material_name = getattr(construction, attribute)
        material = idf.getobject('MATERIAL', material_name)

        # calculate the material's heat capacity and add it to the construction's
        if material is not None:
            thickness = material.Thickness
            density = material.Density
            specific_heat = material.Specific_Heat
            material_heat_capacity = thickness * density * specific_heat
            construction_heat_capacity += material_heat_capacity

    # add the construction's total heat capacity to the model's total
    total_heat_capacity += construction_heat_capacity

print('J/m2*K =', total_heat_capacity)

References from OpenStudio

• LayeredConstruction.cpp
• OpaqueMaterial.hpp

Your questions is for Energyplus, but if you use OpenStudio you can use the following script to get the total heat capacity for all the surfaces in your model as long as you hard assigned the constructions (eg. did not use space types to assign a construction set):

model_surfaces = model.getPlanarSurfaces
building_mass = 0
model_surfaces.each do |surface|
    if not surface.heatCapacity.empty?
        building_mass += surface.heatCapacity.get
    end
end
puts building_mass