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A bug report about load distribution to chillers. 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.

Since I can't find an ExampleFile which meets the conditions above, I reproduced the bug using HVACTemplate-5ZoneVAVWaterCooled.idf. I quickly revised the idf and expidf files to meet the conditions above. The waterside schematic is shown below.

The cooling load in early May is small enough to be handled by one or two chillers as shown below, but all chillers operate, and the cooling load is distributed to them uniformly.

The idf file is here. The version is V24-2-0.

Leaving Chilled Water Lower Temperature Limit of Chiller:Electric:EIR should not be set too low because the actual leaving chilled water temperature during simulation can be lowered to Leaving Chilled Water Lower Temperature Limit. SetpointManager:Scheduled does not necessarily guarantee a constant leaving chilled water temperature.

A bug report about load distribution to chillers. 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.

Since I can't find an ExampleFile which meets the conditions above, I reproduced the bug using HVACTemplate-5ZoneVAVWaterCooled.idf. I quickly revised the idf and expidf files to meet the conditions above. The waterside schematic is shown below.

The cooling load in early May is small enough to be handled by one or two chillers as shown below, but all chillers operate, and the cooling load is distributed to them uniformly.

The idf file is here. The version is V24-2-0.

Leaving Chilled Water Lower Temperature Limit of Chiller:Electric:EIR should not be set too low because the actual leaving chilled water temperature during simulation can be lowered to Leaving Chilled Water Lower Temperature Limit. SetpointManager:Scheduled does not necessarily guarantee a constant leaving chilled water temperature.