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How is pump and fan power calculated? Does E+ actually model liquid and air flow networks?

asked 2015-10-02 14:59:46 -0600

updated 2015-11-09 13:23:05 -0600

Hi community,

When I define a refrigeration loop and run a simulation, I get values for pump and fan power consumption in the report. How are these values calculated? Does openstudio / E+ assume pipe and duct length and flow rates, and actually models the fluid flow or is it a more rough estimation?

Thanks!

Jim

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answered 2015-10-05 10:36:11 -0600

Here's what's happening (assuming you didn't set the flow rates/capacities manually):

  • E+ calculates the heating and cooling load for each zone
  • E+ looks at the Sizing:Zone object to see what the assumptions for heating/cooling supply air temp are
  • Based on the load and the supply air temps, E+ calculates the flow rate of air at that temp that is required to meet the load.
  • The fan power is based on the required flow rate and the user input fan pressure rise. If you don't modify the fan pressure rise, E+ will use the default. You can view/edit the defaults for the pressure rise by clicking on the fan.

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  • If there are hot or chilled water coils on the loop, E+ looks at the Sizing:System for the air loop and the Sizing:Plant object and calculates hot/chilled water flow rates required for the coils to meet their loads.
  • Pumping power is based on the require flow rate and the user input pump pressure rise. If you don't modify the pump pressure rise, E+ will use the default. You can view/edit the defaults for the pressure rise by clicking on the pump.

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Thanks for your answer @aparker. So E+ does not actually model the liquid and air flow networks. Is that correct?

dsfakianakis gravatar imagedsfakianakis ( 2015-10-05 16:04:09 -0600 )edit

@dsfakianakis Yes, E+ does not model the liquid and air flow networks of the HVAC systems.

Yixing Chen gravatar imageYixing Chen ( 2015-10-07 00:14:32 -0600 )edit

@YixingChen Thanks for letting me know!

dsfakianakis gravatar imagedsfakianakis ( 2015-10-08 18:28:06 -0600 )edit
7

answered 2015-10-05 16:38:43 -0600

updated 2015-10-05 16:42:12 -0600

For airflow loops, you can only specify a pressure rise across the fan and it's corresponding efficiency. EnergyPlus is not able to calculate the operating point of the fan based on a fan curve and air system curve.

For liquid loops, you can specify a pressure drop curve for any liquid loop branch. You can also set a pump curve for any pumps in your system. If you do this the pump energy consumption will be calculated based on the operating point (pressure and flow) of the pump as specified by the system and pump curves. To use this feature, you must set the Pressure Simulation Type in the PlantLoop object to "LoopFlowCorrection".

For more information on how the loop flow correction is calculated, you can read this section of the Engineering Reference.

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Hi Neal,

Thanks for the answer, very helpful. Wish I could mark both answers as correct.

Take care,

Jim

dsfakianakis gravatar imagedsfakianakis ( 2015-10-12 15:53:36 -0600 )edit

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Asked: 2015-10-02 14:59:46 -0600

Seen: 239 times

Last updated: Oct 05 '15