Modeling primary-secondary plant loop with VSD pumps on both sides

asked 2020-06-16 20:48:22 -0500

energysim's avatar

updated 2020-06-18 08:20:30 -0500


I am trying to model a large central heating hot water plant consisting of 8 boilers with 2 headered VSD primary HHW pumps and 2 secondary VSD pumps. I am modeling this plant in EnergyPlus using a heat exchanger to connect the primary and secondary loops. The control scheme for the loop is set to sequential.

When I review the results, even though the VSD pump serving the secondary loop varies its flowrate based on the load on the demand side; the VSD primary loop pump runs at constant speed whenever there is any heating load present on the loop. The mass flow rate of the primary pump always matches the sum of the design flow rates for all 8 boilers.

I also checked the supply side flow rate for the heat exchanger which also varies with the load but somehow it doesn't match with the hourly pump flow rate. I even removed the bypass branches on the primary loop (both on the supply and demand sides) but it didn't seem to change anything.

My question is “how do I model the pumping configuration as described above where the primary pump power would vary depending on the active heating plant equipment?”. I chose not to model 8 individual pumps interlocked with each boiler since it wouldn't match with the actual specified plant equipment.

Thanks in advance for any support, Alper

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I have similar issue here.
To simulate a complex cooling plant, I have to use heat exchanger to transfer fluid from one plant loop to another in exatcly same condition (flow rate and inlet&outlet temp.) But with the native operation scheme, I don't know how to properly model it.

szsz's avatar szsz  ( 2020-06-17 21:58:35 -0500 )edit

@energysim could you post a link to your IDF using Dropbox, Box, Google Drive, etc.? That way others can review the inputs for your pumps and other plant loop components to provide better help.

Aaron Boranian's avatar Aaron Boranian  ( 2020-06-20 10:09:24 -0500 )edit

@szsz comment 2: For now, I have to solve it with EMS component to override the pump mass flow rate each run-time to match the required flow rate. With this method both side of heat exchanger is able to have similar flow rate as well as inlet and outlet temperature, but still cannot get exactly same one. Hope some experts help to answer this problem.

Aaron Boranian's avatar Aaron Boranian  ( 2020-06-20 10:11:23 -0500 )edit

@aaron-boranian Here is a link to the IDF file:

Thank you

energysim's avatar energysim  ( 2020-06-25 16:47:39 -0500 )edit