Pump Impeller Efficiency

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Actually, this is not a question. Just wondering if anyone had made the same mistake as my colleagues regarding the calculation of pump power in EnergyPlus.

Generally speaking, Pump input power [W] = Flow rate [m3/s] x Pump head [Pa] / (Motor efficiency x Impeller efficiency). This is described as follows along the Field Names of Pump Classes in EnergyPlus.

Design Popwer Consumption [W] = Design Maximum Flow Rate [m3/s] x Design Pump Head [Pa] / Motor Efficiency x Design Shaft Power per Unit Flow Rate per Unit Head

The unfamiliar word "Design Shaft Power per Unit Flow Rate per Unit Head" is actually the inverse of impeller efficiency, which is described only in Engineering Reference.

For the ASHRAE90.1 Baseline case, the above equation is transformed as follows.

Design Pump Head [Pa] = Prescribed pump power [kW/1000L/s] x 1000 [W/kW] x Motor Efficiency / Design Shaft Power per Unit Flow Rate per Unit Head

Motor Efficiency and Design Shaft Power per Unit Flow Rate per Unit Head for the Baseline case are described in Performance Rating Method Reference Manual.

Shamefully, all my colleagues did not know the above equation. They overlooked Motor Efficiency and Design Shaft Power per Unit Flow Rate per Unit Head, especially the latter. Dozens of ASHRAE Baseline cases they have modlleded in the past have been wrong. I think this happened largely due to their lack of knowledge, but also a little due to EnergyPlus' unkindness.

• When we use HVACTemplete, we cannot input Motor Efficiency and Design Shaft Power per Unit Flow Rate per Unit Head.

• Design Shaft Power per Unit Flow Rate per Unit Head is on the bottom of the Field. I think such an important parameter should be listed further up. Besides, it's blank when the Pump classes are generated from HVACTemplate, which is easily overlooked.

  

I think improving the above two unkindnesses would reduce the number of people making the same mistake.