[Bldg-sim] Appendix G Fan Power Calculation Clarification

[Karen Walkerman]

Hello,

I have seen some discussion on how to separate fan power from EER on the
various list-serves, but never seen an explicit description of exactly how
to go about it.  Below are my calculation methodologies and I'm hoping to
generate some thumbs up/thumbs down discussion and clarification:

>From ASHRAE 90.1 Users manual formula G-A:

EER = (Net Cooling [BTU/h]) / (Total Input Power [W])

     = ((Gross Cooling - Supply Fan Power) [Btu/h]) / (Total Input Power
[W])

Definitions

Total Input Power:  Includes supply and condenser fan power, and condenser
power

Supply Fan Power [btu h ] : this is the heat rejected by the fan to the
supply air stream.  If 100% of the fan power is eventually converted to
heat, then this is 3,413 X Supply Fan KW.


To Calculate the EER, minus the fan, do the following:

Break Total Input Power into Supply Fan Power and condenser fan and
compressor power

I'll use the following abbreviations for subsequent formulas to minimize
typing:

GC : Gross Cooling [btu/h]
SPb: Supply Fan Power [btu/h]
SPw: Supply Fan Power [w]
CP: Compressor Power [w]

For an Appendix G baseline model, we have GC, SPb, SPw, and EER.  So, from
formula G-A, we solve for CP::

CP + SPw = (GC - SPb) / EER

CP = (GC - SPb) / EER - SPw

Now, we can determine the EER, excluding the fan power so:

Modified EER = GC / CP

A few things to discuss:

1.  Is this really appropriate for systems where the fan power is calculated
using the G.3.1.2.9 guidelines?

2.  What is done when the requirements for cooling system efficiency is
listed as a SEER instead of an EER?  Is there an acceptable conversion
factor for use in these calculations?

3.  I this methodology what is intended?  ASHRAE Appendix G, and even the
User's Manual is extremely brief of this.

Thanks,

--
Karen
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