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Pump head influence on cooling load

asked 2018-11-06 14:41:13 -0600

kbk78 gravatar image

updated 2018-11-06 20:16:46 -0600

If we have the pump "Fraction of Motor Inefficiencies to the Fluid Stream" set to 0, why would the pump head have an effect on the cooling load.

In the attached, energy plus version 9, test file that uses purchased cooling the "cooling load" changed from 1,018,159 kBtu to 990,412 kBtu . The only thing I changed was to zero out the pump head.

C:\fakepath\tb.idf.bmp

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answered 2018-11-06 17:58:00 -0600

From the Engineering Reference, section "Pump Heat Addition to the Loop":

Due to the fact that a pump is a mechanical device that acts on the fluid it is circulating, it causes the fluid to increase in temperature. The EnergyPlus model assumes that all pressure increase caused by the pump will eventually be lost due to friction, and that friction will be added as heat to the fluid.

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From the manual:

ShaftPower = PumpPower * PumpMotorEfficiency

PumpHeatToFluid = ShaftPower + (PumpPower - ShaftPower) * FracMotorLossToFluid

If I understand correctly energyplus is assuming all the kinetic energy used to get the fluid moving, results in a identical amount of heat as well?. This is separate from the heat generated by pump inefficiencies.

kbk78 gravatar imagekbk78 ( 2018-11-07 07:33:17 -0600 )edit

Correct, mostly. All of the shaft power is added as heat, and it includes inefficiencies of the actual pump. The drive motor inefficiencies are added to the fluid based on FracMotorLossToFluid.

MJWitte gravatar imageMJWitte ( 2018-11-07 19:23:59 -0600 )edit

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Asked: 2018-11-06 14:41:13 -0600

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Last updated: Nov 06