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Zone VRF does not work with Airloop VRF

asked 2022-09-17 15:37:13 -0500

Keigo's avatar

updated 2022-09-17 21:29:02 -0500

I have trouble modelling VRF. The main HVAC system of my model is VRF: Heat Reclaim Ventilator with DX-Coil as DOAS + Indoor Units for handling internal load. I referred to this post to model Heat Reclaim Ventilator with DX-Coil.

The problem is that Coil:Cooling:DX:VariableRefrigerantFlow in some zones does not work at all. Coil Total Cooling Rate of the coils is 0W. I got so many unmet hours in cooling. Heating coils work fine in winter. This occurred only when ZoneHVAC:TerminalUnit:VariableRefrigerantFlow in the AirLoop and ZoneHVAC:TerminalUnit:VariableRefrigerantFlow in some zones were connected to the same AirConditioner:VariableRefrigerantFlow as shown on the left side of my scketch below.

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This is not the end of the problem. My model has 85 nos. of AirConditioner:VariableRefrigerantFlow in total and some VAV systems for undesigned tenant area. Most of the VRF outdoor units are divided into two types from the begining: for DOAS only and for Zone indoor unit only. I tried removing the unrelecant VAVs and VRFs in order to focus on the target VRFs, but after that, I found that the target Coil:Cooling:DX:VariableRefrigerantFlow worked fine even though AirLoop ZoneHVAC:TerminalUnit:VariableRefrigerantFlow and Zone ZoneHVAC:TerminalUnit:VariableRefrigerantFlow were connected to the same AirConditioner:VariableRefrigerantFlow! I was very confused.

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I tried everything I could think of such as autosizing and changing parameters in various classes, but I could not identify why the Coil:Cooling:DX:VariableRefrigerantFlow did not work.

Is this a bug that occurs under specific conditions? Or am I missing my wrong setting?

I also tried to reproduce this problem with an ExampleFile: VariableRefrigerantFlow_5Zone_wAirloop.idf, but could not. Does the number of VRF in the idf file have anything to do with the problem? I have no idea.

Three idf files and the results are here. The idf version is v9-6-0.

Any suggestions would be appreciated.

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answered 2022-09-24 08:33:48 -0500

Keigo's avatar

updated 2022-09-24 08:49:10 -0500

After a little more investigation, I found that the bug occurs when the following two conditions are met:

  • ZoneHVAC:TerminalUnit:VariableRefrigerantFlow in the AirLoop and ZoneHVAC:TerminalUnit:VariableRefrigerantFlow in some zones are connected to the same AirConditioner:VariableRefrigerantFlow
  • There is another AirLoopHVAC which does not have ZoneHVAC:TerminalUnit:VariableRefrigerantFlow.

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I have narrowed down the cause of the bug to some extent, which is OK for me for now.

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Asked: 2022-09-17 15:37:13 -0500

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Last updated: yesterday