Possible to combine zones from different shells into one zone?

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I have a building that requires multiple shells. It is a two story building, that requires different zoning on each floor. My question: Is there a way to combine zones from different shells into a single zone? For instance, I have two spaces (each space is its own shell) that are not right next to each other, but they have the same orientation, hvac system type, etc. I would like to combine them into a single zone because they have the same space type. I was just hoping to find a way to make my model more accurate. Instead of each space (and corresponding zone) gettings its own RTU, I would like them to share the same RTU, and don't know any other way to have them do this other than making them into a single zone. But, I don't know how to accomplish this or know if it is really even necessary. I know it would be easier if they were part of the same shell, but this isn't possible due to the geometry of the building, etc. It just doesn't seem that two hvac units would be as efficient as one unit, but this is the only way I currently know how to model it. Any help would be greatly appreciated. Thanks, Winston
wshurtz's picture
Joined: 2011-05-23
Reputation: 0

There are a few ways to skin the cat.

Easiest may be to

- Re-assign the parent system for one set of zones so all the
targeted plenums/below-ceiling zones are under a single system (it's a
property you can find after double-clicking a zone in the tree in the
airside tab.

- Right-click and delete the "childless" system

- While you're still under the airside tab, take note of which
zone the thermostat is located for the system (colored red in the visual
"map" after highlighting a system/zone-group) and adjust to match actual

- Optional: if two zones are really geometrically one space and
you want the loads in one to intermingle relatively freely with those in
the other, modify or create an internal partition thermally connecting
them as an "air" wall.

You could take other steps to literally make them one larger space /
zone, but from your description the above approach would be faster,
simpler and have the same net effect.

It doesn't really matter whether the spaces are in the same or unique
shells by the way.

Whether there's a significant overall difference between one vs. two
units is would in part hinge on whether the divided spaces have
significantly different loads or scheduling hour-by-hour before being
combined (example: a bunch of exterior glazing on only one side).
Somewhat likely coming out of the wizards if you have two shells with
different proportional occupancies as those weighted averages affect the
outcome of the generated per-shell scheduling.

Hope that helps!



Nick-Caton's picture
Joined: 2011-09-30
Reputation: 805