Variable CHW Flow Chillers Operate unexpectedly

[keigo-nomura]

Issue overview

The bug is reported in detail on UnmetHours. Below is an extract from UnmetHours.

The bug occurs when the following conditions are met. The last condition is particularly important.

1. There are multiple chiller objects e.g.Chiller:Electric:EIR.
2. Each chiller has a primary chilled water pump.
3. The primary chilled water pumps are Pump:VariableSpeed, and Chiller Flow Mode of Chiller:Electric:EIR is set to LeavingSetpointModulated.
4. Design Minimum FLow Rate of Pump:Variable:Speed is not 0.
5. Load Distribution Scheme of Plant Loop is SequentialUniformPLR, SequentialLoad or Optimal.
6. Leaving Chilled Water Lower Temperature Limit of Chiller:Electric:EIR is the same as (or closer to) the leaving chilled water temperature setpoint specified by a setpoint manager e.g. SetpointManager:Scheduled.

When the cooling load is small enough to be handled by one chiller, only the chiller should be ON and the remaining chillers should be OFF because the load distribution is set to be sequential, but this is not the case under the above conditions. The cooling load is distributed uniformly to all or most of chillers as if Load Distribution Scheme is UniformLoad or UniformPLR. That's the bug.

Operating System (Multiple choices)

Windows

Operating System Version

11

Version of EnergyPlus

24.2.0

Unmethours link or helpdesk ticket number

https://unmethours.com/question/101114/variable-chw-flow-chillers-operate-unexpectedly/

Defect file

Please find the defect file in the following link.

https://drive.google.com/drive/folders/1AxBgEGGMWMFcnhZhwLuEtCn1eCVr1HCw?usp=drive_link