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

edit

Hi,

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