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Zone Multipliers in OpenStudio

asked 2014-11-18 15:03:22 -0500

ivanadriane's avatar

updated 2014-11-18 16:31:54 -0500

Hi, I am working on my first project in OpenStudio and turns out my model is an 89 story building. I was wondering if there is a function in OpenStudio that would allow me to use a zone multiplier. Many of the stories in my building have reiterating geometries as well as identical boundary conditions, I was wondering if there was a way I could group these spaces and use a zone multiplying function in OpenStudio when doing my analysis.

The reason for this is that the 89 story model also has about 1,200 individual spaces which makes the OpenStudio plug-in run incredibly slowly in Sketchup.

Thanks for your help.

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answered 2014-11-18 15:36:51 -0500

updated 2014-11-20 09:21:46 -0500

There is, you can add zone multipliers to your OSM using the Inspector (magnifying glass icon) in the OpenStudio Plugin or to the Thermal Zones tab of the OpenStudio App.

Typically, a multiplier is applied to the zone(s) on the middle floor of the high rise and the lower/upper floors are omitted from the model which reduces simulation time. Below is an image of the Large Office IDF from the DOE Commercial Prototype Buildings and DOE Commercial Reference Buildings which might be helpful.

Zone Multiplier in the SketchUp Plugin image description

Render by Boundary Condition showing adiabatic ceilings and floors image description

Zone Multiplier in OpenStudio 1.5.0 image description

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Matthew, thanks for pointing out the function in the OpenStudio Inspector as well.

ivanadriane's avatar ivanadriane  ( 2014-11-18 16:40:05 -0500 )edit

I have used the zone multiplier several times, but when I use it I do not have a gap in between the floors like you show in this image. How are you surface matching these floors? Did you just manually move them to make it look correct? Or did you make the floors and ceiling adiabatic.


TaylorRoberts's avatar TaylorRoberts  ( 2014-11-19 13:46:57 -0500 )edit

Good question @TaylorRoberts. I didn't build this model it's the Large Office IDF from the DOE proto/ref buildings, but the "interzone" floors and ceilings are adiabatic. One reason to model a high rise this way is to account for the microclimate effects of height (and the associated heat transfer through the envelope) which in your case would be a trade off with interzone conduction. See @David Goldwasser's answer to this question.

MatthewSteen's avatar MatthewSteen  ( 2014-11-20 08:55:58 -0500 )edit

answered 2014-11-18 15:27:00 -0500

updated 2014-11-18 15:29:09 -0500

Thanks you for asking this question. You are correct, you do not want to model all of the floors; it would take long to model and a ong time to run. The thermal zone multiplier is exposed in the thermal zone tab of OpenStudio 1.5. It is also in earlier versions of OpenStudio but is a little more hidden. If you are using pre-1.5 version I can provide specific instructions.

  1. On a smaller building you could geometrically model your building as three stories, and then set the zones on the mid-floor to a higher zone multiplier than the default value of 1.
  2. You would also want to set the interior floor and surfaces to adiabatic boundary conditions. I would first run surface matching, assuming your three stories were modeled adjacent to each other. Then I would use surface search in SketchUp to find all floor and ceilings that have a surface boundary condition. Run the user script to change the boundary conditions to adiabatic, it will allow you to choose a construction. You want to make sure you pick a construction since adiabatic surfaces in OpenStudio do not inherit from a construction set.
  3. Optionally you can move your top floor and mid floor to a different height. If nothing else this make it obvious to someone else opening your model what the intent is, but there can also be other impacts of the position.
  4. Since your building is so tall, you may want to consider modeling more than one mid floor. I'll let others chime in on how many stories is appropriate for a mid-floor multiplier on high rise buildings, but maybe something around 10-20 floors each? Two factors that would impact this decision is shading by adjacent structures, and effect of wind at different heights above the ground.
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David, if the zones didn't repeat and we actually end up with a 1200 zone model, would openstudio continue to be this slow in the future?

EmirPekdemir's avatar EmirPekdemir  ( 2014-11-18 16:15:18 -0500 )edit

David, Thanks for your help, this should help with my model a great deal.

ivanadriane's avatar ivanadriane  ( 2014-11-18 16:38:44 -0500 )edit

@ivanadriane, your welcome. @EmirPekdemir. Modeling a large number of zones will always be slower to model and to simulate. Each zone and surface is more calculations to do at each time step. Part of the art of modeling is deciding what level of detail gives you what you need without adding too much detail that burdens your workflow. I have considered a specialized zone multiplier that would provide a visualization of the additional floors. This could also make shading surfaces out do them, which could be useful in a non rectangular building that casts shadows on itself.

David Goldwasser's avatar David Goldwasser  ( 2014-11-18 22:41:27 -0500 )edit

Thanks David, looking forward to new features :)

EmirPekdemir's avatar EmirPekdemir  ( 2014-11-19 09:33:17 -0500 )edit

@EmirPekdemir, this isn't a planned features just something I was thinking about. If someone really wanted to prototype this, one approach would be to code logic in the zone name or the spaces in that zone identifying where the duplicate copies should exist. Then at run time a measure could make shading surfaces from the exterior surfaces of the zone with the non-1 multiplier. You could also just add measure to change multiplier by story, with input for base z height and delta z per instance.

David Goldwasser's avatar David Goldwasser  ( 2014-11-19 10:33:12 -0500 )edit

answered 2014-11-19 11:24:47 -0500

One of my fantasies is to actually bake this functionality into EnergyPlus, i.e., have EnergyPlus internally recognize when zones are similar, simulate only a single representative from each set, and do the multiplication internally. This could also probably be done as a (fairly intense) measure. Would be a good winter break project...

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Asked: 2014-11-18 15:03:22 -0500

Seen: 2,260 times

Last updated: Nov 20 '14