Set People and Lights for Internal Mass

edit

Although I would not recommend using the InternalMass object to model changes in thermal mass for floors (and ceilings for multi-floor buildings), I guess you could model certain aspects of building materials using this method.

From the Input Output Reference document:

InternalMass is used to specify the construction/material parameters and
area of items within the space that are important to heat transfer
calculations but not necessarily important geometrically. (For example,
furniture within the space - particularly for large spaces). Internal mass
can also be used for internal walls that are not needed (when
FullInteriorAndExterior Solar Distribution is in effect) for solar 
distribution or to represent many, if not all, interior walls when solar
is distributed to the floors only.

In this case, the use of Lighting Level or Equipment Level can be used to model internal gains. Since, for a given building model, the floor area is fixed, changing the internal loads input from W per floor area to W is not an impediment to the model.

If you are using OpenStudio and have multiple spaces in a single thermal zone, an internal mass object will be made for each pair of surfaces that are matched by spaces within the zone. The internal mass object has an area and a construction. It doesn't matter for this what the floor area or number of people are.

Beyond internal mass made by matched surfaces within a zone you can also add internal mass using the internal load tab of OpenStudio. In addition to just defining an area, you can also define an internal mass area per floor area, or per person.


Lastly if you use interior partitions in your model you can check a box to have them export as internal mass objects.