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NREL / EnergyPlus

EnergyPlus™ is a whole building energy simulation program that engineers, architects, and researchers use to model both energy consumption and water use in buildings.
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Pump:ConstantSpeed operating at less than full flow but consuming full power #10821

Open mjwitte opened 1 week ago

mjwitte commented 1 week ago

Issue overview

User file has an Intermittent Pump:ContantSpeed on the primary ChW loop with an HX serving the secondary ChW loop. Even though it's constant speed, the pump mass flow rate varies, but the pump power consumption is always at full power.

image

In Pumps::SetupPumpMinMaxFlows constant speed pumps only force full flow when set to Continuous (contrary to the docs). https://github.com/NREL/EnergyPlus/blob/9c7c2a6d79740945a4d75b9a375928537daaf0bc/src/EnergyPlus/Pumps.cc#L1691-L1695

But then later in Pumps::CalcPumps, the power calc is the same for variable speed and constant speed pumps: https://github.com/NREL/EnergyPlus/blob/9c7c2a6d79740945a4d75b9a375928537daaf0bc/src/EnergyPlus/Pumps.cc#L1896-L1903

But the PartLoadCoef for the constant speed pump are 1,0,0,0, so this results in full power regardless of flow rate. https://github.com/NREL/EnergyPlus/blob/9c7c2a6d79740945a4d75b9a375928537daaf0bc/src/EnergyPlus/Pumps.cc#L577-L583

Maybe that last comment about riding the pump curve is clue?

For this file, there are bypass pipes available on both the supply side and demand side, so it seems the pump should be running at full flow.

  1. Why is the pump running at less that full flow when there are bypass pipes available?
  2. Why is intermittent vs continuous pump handled differently in SetupPumpMinMaxFlows?
  3. Maybe this isn't an issue with the pump, but with something else in this plant loop?

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