Variable Speed Primary Chilled Water Pumps Operate Unexpectedly
A bug report about chilled water pumps. The bug occurs when the following conditions are met.
- There are multiple chiller objects e.g.
Chiller:Electric:EIR. - Each chiller has a primary chilled water pump.
- The primary chilled water pumps are
Pump:VariableSpeed, andChiller Flow ModeofChiller:Electric:EIRis set toLeavingSetpointModulated. Design Minimum FLow RateofPump:Variable:Speedis not 0.Load Distribution SchemeofPlant LoopisSequentialUniformPLR,SequentialLoadorOptimal.
I expect that each chilled water pump is interlocked with each dedicated chiller, but actually all chilled water pumps operate when there is a cooling load even if the load is small enough to be handled by one chiller. That's the bug. Pump Control Type is set to Intermittent.
Since I can't find an ExampleFile which meets the coditions above, I reproduced the bug using HVACTemplate-5ZoneVAVWaterCooled.idf. I quickly revised the idf and expid files to meet the conditions above. The waterside schematic is shown below.
The bug is easy to spot on 7 and 8 May in the charts below. Chiller2 to 4 do not operate but all the chilled water pumps operate on those days.
The idf file is here. The version is V24-2-0.
That's a great demonstration. Bug reports should ideally be reported at https://github.com/NREL/EnergyPlus/is... though.
@Julien Marrec If no one answers and this is more likely to be a bug, I'll post it on GitHub.
Reported on Github.
https://github.com/NREL/EnergyPlus/issues/10964
It seems the PLRs differ among the active chillers, which doesn’t align with the expected behavior of SequentialUniformPLR. Do you have any insights on why that might be happening?
I haven't looked into the code. It is beyond the scope of user's voluntary bug reporting.