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How to deal with unknown system nodes in osm files ?

asked 2016-03-09 16:13:59 -0600

updated 2016-03-09 17:15:17 -0600

Look at the following airloop:

image description

When defining required nodes for a SetpointManager:MixedAir, I encountered two problems:

(1) What's the appropriate Fan Outlet Node for the SetpointManager ? Note that the FanOutletNode in reality resides within the UnitarySystem, which apparently is not accessible in Openstudio for referencing.

(2) Where are these nodes with those nasty UUID-names in the system, what is their purpose, how can they be located ? (These nodes apparently are nowhere visible in OpenStudio for users)

What's your advice ?

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answered 2016-03-10 08:55:27 -0600

The unitary systems have control built into them, so you don't need any setpoint managers unless there are other components outside the unitary that require control. I suggest that you just remove all of the setpoint managers on this system. You do need to select the control zone in the unitary system settings.

image description

In the situations where you do need specify the mixed air setpoint manager, you can leave the fan inlet / outlet node settings blank and OpenStudio will fill in default values on export to idf format.

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Thanks for your instructive answer, Kyle. But what about the second part of my question regarding UUID-names nodes ?

OS-user-AT's avatar OS-user-AT  ( 2016-03-11 07:05:55 -0600 )edit

Those node names are certainly obnoxious. They happen when a node isn't explicitly given a name. In other words they are the guaranteed unique name generated by the low level OS gears. I've tried to root many of them out, but obviously some remain. Generally they are related to internal nodes of zone hvac, terminals, and unitary systems. You shouldn't need to interact with them often.

Automatic node naming is tough. If we set the node name to a derivation of the system name, what happen when you change the system name? What if you write your own custom name that you want to stick?

Kyle Benne's avatar Kyle Benne  ( 2016-03-11 07:53:50 -0600 )edit

answered 2016-03-09 18:32:26 -0600

(1) The Mixed Air SPM object you're trying to use is meant for air handlers, where the heat added by the supply fan is taken into account in order to deliver air at the desired setpoint temperature. Since you're using a unitary system, it might make more sense to use a Scheduled SPM instead.

(2) The best way to find the nodes with the UUID names is to open the OSM in a text editor and search for the UUID. My guess is that they are nodes associated with zone HVAC equipment like FCUs, since these don't show in OpenStudio HVAC diagrams where you can edit the node name.

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Asked: 2016-03-09 16:13:59 -0600

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Last updated: Mar 10 '16