Different behavior of compressor speed and cycling ratio between VRF FuildTCtrl heat pump and HR model

[yujiex]

Issue overview

Comparing the following two models, VariableRefrigerantFlow_FluidTCtrl_HR_5Zone.idf and VariableRefrigerantFlow_FluidTCtrl_5Zone.idf, we can see that the compressor speed of the heat pump model never gets below 1500 (corresponding to the speed at loading index 1), while the compressor speed of the HR model will continuously vary from 0 to 6000+. Furthermore, in HR model, the compressor speed is only less than 1500 when cycling ratio is 1.

Comparing the cycling ratio at different operation mode using the example file VariableRefrigerantFlow_FluidTCtrl_HR_5Zone.idf, we can see that the system only cycles in cooling-only (mode 1) and heating-only (mode 2). In simultaneous heating-cooling mode (mode 3), cycling ratio is always 1. The figure on the right shows the output for a larger-capacity case, where "Rated Evaporative Capacity" is changed to 700000W, much larger than the outsized capacity. In this case, the cycling ratio both reduced in heating-only and cooling-only mode (they never reach 1), but the cycling ratio during simultaneous heating-cooling mode still remains 1.

The following weather file is used with the two example files (annual simulation is run on the command line with -a flag)
5A___USA_IL_Chicago-Midway.AP.725340_TMY3.epw.zip
The following are the idfs
idfs.zip

Details

Some additional details for this issue (if relevant):

• Platform (MacOS, 13.5.2)
• Version of EnergyPlus (23.1)
• Unmethours link or helpdesk ticket number

Checklist

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• Defect file added (list location of defect file here)
• Ticket added to EnergyPlus Defect Complexity (Github Project)
• Pull request created (the pull request will have additional tasks related to reviewing changes that fix this defect)