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# AirLoopHVAC:UnitarySystem Error

I am using OS 2.4.0. I have been trying to model a DOAS unit with separate unitary water to air units set to setpoint control and I have had nothing but issues. One error is that once I set it to setpoint control the electric reheat coil keeps asking for a control node which I cannot enter since it is not accessible.

** Severe  ** Coil:Heating:Electric "ELEC HTG COIL 13"
**   ~~~   ** ... Missing control node for heating coil.
**   ~~~   ** ... enter a control node name in the coil temperature setpoint node field for this heating coil.
**   ~~~   ** ... use a Setpoint Manager to establish a setpoint at the coil temperature setpoint node.


I am not sure I am using the right setpoint managers for this approach. I really want to control to a supply air temperature and not a zone temperature. Any ideas? Here is a link to the test file I am working with: Test Case Doas.osm

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There have been previous questions on the topic such as here and here.

Looking at your model, you have two AirLoopHVAC:UnitarySystem objects, and each houses four components: a Fan:OnOff, a Coil:Cooling:WaterToAirHeatPump:EquationFit, a Coil:Heating:WaterToAirHeatPump:EquationFit and a Coil:Heating:Electric (the reheat).

OpenStudio doesn't create the inner nodes between these components until Forward Translation happens, which means you cannot use "Setpoint" mode with a Unitary that houses more than one component.

So you have two options:

• Use a unitary with many components, but use the "Load" control (there have been problems in simulation times reported in one of the questions I linked)
• Use one unitary system to wrap your Coil:Cooling:WaterToAirHeatPump:EquationFit and one unitary forCoil:Heating:WaterToAirHeatPump:EquationFit, put as "Septoint" mode an place a setpoint manager on the outlet node.
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Julien, I had read both of the post you referenced before so I was hoping you would respond to my question. My struggle is how do you define which coil the AirLoopHVAC:UnitarySystem will use or is it defined by whichever setpoint manager you use? Also, specifically which setpoint manager would you recommend? I was trying to use setpoint manager scheduled because I want to control to a constant leaving air temperature. Is that even possible? It looks like from the first link you used setpoint manager single zone cooling and single zone heating.

( 2018-02-13 06:35:23 -0500 )edit

One other thing on this. This issue I am having is with the electric reheat. I cannot set the temperature setpoint node in the OS. Exporting to IDF and running the IDFEditor I can change the setpoint node for the electric heat coil to the setpoint managers and it runs fine. When I look at the *.osm file the "Temperature Setpoint Node Name" is not a parameter under the electric heating coil but it is in the *.idf file.

Not a big issue except that I need to run in the OS API to access measures for converting the loads to GLHEPro and running well field sizing analysis.

( 2018-02-13 07:18:23 -0500 )edit

You have to create your unitary systems with the coils using the openstudio bindings (ruby by default). Can't do it in the OS App. In your case, you can place a SPM:Scheduled on the supply outlet, and you can try with a SPM:MixedAir or a SPM:Scheduled on each coil outlet. If you go this route (one unitary per coil), your electric reheat coil and the fan are placed directly onto the airloophvac (not in a unitary).

( 2018-02-13 10:45:11 -0500 )edit

Not sure about the Temperature Setpoint Node Name for Coil:Heating:Electric but it's in the OS IDD here. I also don't think you need that, because if you control it on load (leave that blank) and have an appropriate setpoint manager, it'll work.

( 2018-02-13 10:45:57 -0500 )edit