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Include Thermal Mass of Furniture and Internal Partitions in OpenStudio

asked 2021-09-15 11:49:55 -0600

Alejandro Lopez gravatar image

I am having difficulties artificially adding thermal mass into my building model without adding geometry into the building.

I have developed an apartment building very similar to the Highrise Building in the Create DOE Prototype Building measure. Currently, residential apartments in the model do not have any internal partitions, the reason being that including schedules for bedrooms, bathrooms, and common spaces can be very tricky. In reality, these partitions would be there, and in fact, they would store some thermal energy, which would cause slightly lagged temperature responses in the apartments. This is also true for furniture in the apartment.

This post ( asks a similar question. However, the link provided in the answer ( does not explain how to add the thermal mass of internal partitions and furniture into each apartment. Instead, the link describes a grouping method that constrains heat transfer to a selected group of spaces.

I am also unsure as to how I would even calculate the thermal mass offered by a partition or a piece of furniture.

Is there a way to simply factor in the thermal mass furnishing and partitions? Alternatively, is there a tutorial explaining how I can calculate the thermal mass of different pieces of furniture and partitions and add them one by one into a space?

Many thanks!

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answered 2021-09-15 14:26:30 -0600

The grouping that was described in the EnergyPlus example is just grouping within a single zone (for multiple offices being modeled as a single zone). In the OpenStudio Application you can access internal mass object through the internal loads tab. It requires you to choose a construction for the internal mass along with a square footage. You can add one or multiple internal mass objects to a space/zone depending on what you need. And in your case you may need to add these to each space/zone.

There are two other approaches to do this in OpenStudio. One is to model each unit a a space and then combine multiple spaces to a zone. OpenStudio will convert the space that are not part of the zone boundary to internal mass objects when converting to an EnergyPlus file prior to simulation. You can also create interior partitions in OpenStudio which is a surface group that lives within a space. OpenStudio interior partitions can be converted to internal mass objects when OpenStudio converts to an EnergyPlus IDF file.

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Thanks @david-goldwasser! I am thinking that the approach you described in the first paragraph could be used to create furnishing, and the ones in the second paragraph can be used for the partition. Would using different thermal mass approaches for different elements mess with my model?

Alejandro Lopez gravatar image Alejandro Lopez  ( 2021-09-17 08:43:04 -0600 )edit

It shouldn't mess with you model, but keep in mind that even though interior partitions have a position within the zone, that position isn't saved when it is converted to internal mass. The primary reason interior partitions are in OpenStudio are for daylighting analysis in Radiance.

David Goldwasser gravatar image David Goldwasser  ( 2021-09-17 10:34:22 -0600 )edit

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Asked: 2021-09-15 11:49:55 -0600

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Last updated: Sep 26 '21