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Do DX systems overestimate fan usage in OpenStudio?

Hi. I was looking at the DX cooilng coil object in OpenStudio and observed that it contains evaporator fan information. I already have a supply fan in my airloop (which presumably would be functioning as an evaporator fan in reality). This has led me to wonder if fan usage is being double-counted here. It seems that I am required to have a fan object in my airloop despite the fact that the DX coil supposedly has a fan built into it. Any thoughts?

Thanks!

jbatt's avatar
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jbatt
asked 2018-10-29 14:44:38 -0500
__AmirRoth__'s avatar
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__AmirRoth__
updated 2019-04-07 10:09:43 -0500
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The evaporator fan power input you see in the DX coil object is for calculating standard ratings (e.g., SEER or IEER). This input is not used during the simulation.

Coil:Cooling:DX:SingleSpeed,
  N5 , \field Rated Evaporator Fan Power Per Volume Flow Rate
  \note Enter the evaporator fan power per air volume flow rate at the rated test conditions.
  \note The test conditions vary external static pressure based on total cooling capacity.
  \note This value is only used to calculate Seasonal Energy Efficiency Ratio (SEER), Energy
  \note Efficiency Ratio (EER), Integrated Energy Efficiency Ratio (IEER), and the Standard
  \note Rating (Net) Cooling Capacity which will be outputs in the EnergyPlus eio file.
  \note This value is not used for modeling the evaporator fan during simulations.
  \type real
  \units W/(m3/s)
  \minimum 0.0
  \maximum 1250.0
  \default 773.3
rraustad's avatar
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rraustad
answered 2018-10-29 14:50:12 -0500
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Great thanks! So my follow-up to that is: would the SEER/IEER calculated account for the the supply fan or just the DX coil (i.e. should I give my supply fan an efficiency of 100%?)?

jbatt's avatar jbatt (2018-10-29 15:38:40 -0500) edit
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Using a supply fan with 100% efficiency won't give you an accurate simulation result. Set up your supply fan to perform like a supply fan.Then set this input to mimic that fan's power so that the DX coil model can calculate rated performance accurately. The DX coil model will calculate rated performance before the simulation starts then will use the actual supply fan to perform the simulation. After the simulation look in the eio file for DX coil rated performance information.

rraustad's avatar rraustad (2018-10-29 19:22:44 -0500) edit
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