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Partition walls inside same zone

asked 2015-06-11 08:41:58 -0600

Waseem gravatar image

updated 2015-07-11 10:56:40 -0600

How to model rooms combined as a single zone? Should they have partition wall between them or not? Obviously this will only apply to the rooms which are adjacent to each other not the one which are apart but considered as same zone. If adjacent rooms are kept at same conditions then those partition walls will act like adiabatic walls (no heat transfer). How you guys model this situation?

What if the rooms (considered as one zone) has slightly different number of occupants? Another concern could be that modelling partition walls will also increase simulation time for a larger building.

Also, do you guys model doors? Does modelling them has large impact on energy consumption? I am just trying to save some computational time and was thinking of different options. Any ideas to reduce computational time will be appreciated as well. :)

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@Waseem I changed your unique 'computational-time' tag to the existing and more appropriate 'simulation-time'.

MatthewSteen gravatar image MatthewSteen  ( 2015-06-13 09:17:17 -0600 )edit

@MatthewSteen: Thanks :)

Waseem gravatar image Waseem  ( 2015-06-15 03:54:48 -0600 )edit

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answered 2015-06-11 09:32:35 -0600

In OpenStudio, you can combine multiple spaces (modeled as individual volumes, with their own internal load values) that have similar temperature setpoints and HVAC equipment into a single thermal zone. If the spaces have adjacent surfaces, OpenStudio will translate those surfaces to Internal Mass objects in EnergyPlus, calculated from the surface constructions.

The impact of doors would likely depend on the size of the building and number of doors. I've typically neglected them for large whole-building models. I imagine they add to simulation time as any additional surface would.

Some more information on reducing run-time can be found in the 'Tips and Tricks' document, as well as research papers and this Unmet Hours question.

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Thanks for your answer. So, in normal practice (regardless of simulation software), do modelers include partition walls or not?

Waseem gravatar image Waseem  ( 2015-06-11 09:53:56 -0600 )edit

Also, just to mention, my model take a bit longer to simulate if I combine rooms into different zones and when I leave each room as a separate zone then the computation time is a bit less (half a minute difference). Any ideas, which is the best practice (leave rooms as separate zones or combine them)?

Waseem gravatar image Waseem  ( 2015-06-11 10:16:12 -0600 )edit

As a consultant primarily using OS I include partition walls to account for thermal mass. Whether or not the spaces are grouped into a single thermal zone depends on the actual HVAC design and modeling simplifications I might choose. For example, when working on a large model (800,000+ ft2 currently) I would group thermal zones by exposure and use zone multipliers to reduce sim time.

MatthewSteen gravatar image MatthewSteen  ( 2015-06-13 09:22:08 -0600 )edit

@MatthewSteen: The Zone Multiplier will help when you have same dimension zones, right? Also, @MJWitte mentioned in This thread that combining zones can increase simulation time due to increase in internal thermal radiant exchange. So this means it is OK to leave rooms as separate zones. Agree or any comments?

Waseem gravatar image Waseem  ( 2015-06-15 03:59:34 -0600 )edit

Yes, it's meant to be used when the model has multiple zones with the same attributes. It's important to differentiate between spaces and zones. Spaces are unique to OS providing a way to partition zones and can be thought of as a child object of an EP zone. I don't know what you're trying to model - a research scenario or a design scenario - so I can't comment on which approach is more appropriate, combining rooms into a single zone or separating into individual zones. What equipment is serving the rooms/zones and where are the thermostats?

MatthewSteen gravatar image MatthewSteen  ( 2015-06-15 14:02:16 -0600 )edit

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Asked: 2015-06-11 08:41:58 -0600

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Last updated: Jun 13 '15