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# How to model internal surfaces inside a zone in energyplus

Anonymous

Hello all,

I have a question about how to model internal surfaces in a zone in enrgyplus. According to the following passage from "GettingStarted" document which describes how to define equivalent surfaces:

"Define all heat storage surfaces of the same construction within a zone as a single surface. The size of the single surface is obtained by summing the individual surface areas exposed to the zone. Thus, if a partition is completely within a zone (both sides of the partition are exposed to the zone), the area of each side must be added to the area of the equivalent surface. On the other hand, if the partition separates two zones, the area of only one side should be added to the equivalent surface."

Does the passage mean that I can draw the interior partition inside of a zone as a single surface with the same height of the zone, although it may exceed from the borders of the zone (just like the attached link above or picture below)?

Does Energyplus recognize the partition totally as a thermal mass inside the zone, though part of it is located outside of the zone?

Should I define the surface as an adiabatic boundary condition? Should the surface area be doubled?

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Anonymous, there are a few ways you can approach what you are trying to do.

1. You can model the zone as a single space (assigned to one zone). Inside of this you can create an interior partition group (similar to shading group) and then draw one or more interior partition surfaces. These surfaces should generally be drawn where they exist and not go outside of the space they are in. When running a daylighting analysis with Radiance, these partitions impact the daylighting analysis. When running EnegyPlus, these are converted to internal mass objects,described here. OpenStudio does also allow you to directly make internal mass objects, under the internal load tab, and bypass making interior partitions.
2. You can model each of the rooms as their own space in OpenStudio and then assign them all to a single zone. You don't have to worry about making interior partition objets or internal mass objects in OpenStudio. You do however have to run surface matching so OpenStudio can identify inter-space surfaces. When multiple spaces are in the same zone, inter-space surfaces that are in the middle of the zone will be translated to EnergyPlus as internal mass objects.
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@David Goldwasser, from this EnergyPlus link you provided, it appears that the Internalmass object is used to take the place of all interior partitions, furniture, equipment, AND interior constructions? So, if this object is used, EnergyPlus ignores the interior constructions for the purposes of inter-zone energy exchange (thermal mass) calculation? It seems that, when using this object, the modeler would need to account for not only the added interior furnishings, but also the interior walls, floors, and ceilings?

( 2020-06-05 12:48:03 -0500 )edit

Heat transfer surfaces should be used at thermal zone boundaries, so interior walls and floors that sit between two zones should not be modeled as internal mass. Internal mass objects are intended to model additional mass beyond what is included in the heat transfer surfaces.

( 2020-06-05 13:43:14 -0500 )edit

Thank you David!

( 2020-06-05 15:14:51 -0500 )edit

Your question seems rather bizarre. It would really help if you can specify your purpose of the modeling.

In general, a zone means uniform temperature. A partition in a zone only serves as thermal mass.

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Actually, I have 3 rooms in a zone with the same condition and interior wall construction. But instead of modeling all internal walls one by one in Energyplus, I want to draw a single partition with double length of the sum of all internal walls in open studio. Then I'll import the model into the Energyplus to calculate the thermal loads. Therefore, when I draw the partition , it exceeds the physical borders of the zone.

Does Energyplus recognize the partition totally as a thermal mass inside the zone, though part of it is located outside of the zone?

( 2019-08-23 01:27:25 -0500 )edit

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