Question about ASHRAE 90.1 Baseline equipment efficiencies.Project is using System 5 with a Load of around 400kBtu/h. Table 6.8.1A shows the minimum efficiency to be 9.8

Now to my question:

In my baseline (energyplus /openstudio) model. I have been entering my EER (9.8) as COP(2.872) under an input in the DX Coil named "Rated High Speed COP". But when I look at the energy plus equipment summary output tables for DX cooling coils I see a rated standard COP(w/w) output of 2.55 and a EER (Btu/W-H) of 8.71. To try and find a solution I went into the eneryplus reference material and saw that it said that the COP input is "Gross cooling capacity divided by power input to the compressor and out door fan, but DOES NOT include supply fan heat or supply fan electrical energy input." So I was not sure if if those lower COP and lower EER values in the output table would be considered (by LEED Reviewer) correct or if I should try and add the missing supply fan heat and electrical energy input so that I can increase my EER and COP values to match 90.1. Then I thought I should take another look at ASHRAE G3.1.2.1 Equipment efficiencies and saw it said " all HVAC equipment in the baseline building design shall be modeled at the minimum efficiency levels, both part load and full load, in accordance with section 6.4. Where efficiencies ratings, such as EER and COP, include fan energy, the descriptor shall be broken down into its components so that the fan energy can be modeled separately". So it sounds like I am not suppose to include my supply fan energy in my coil EER. So does that mean I need to remove the supply fan power from my 9.8 EER so that it matches the energyplus input description?

Thanks in advance,

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F S

LEEDuser Basic Member

0 thumbs up

Sun, 11/05/2017 - 22:03

I believe i found my answer in this document on page 37 and 38

Jean Marais

b.i.g. Bechtold DesignBuilder Expert

LEEDuser Basic Member

581 thumbs up

Mon, 11/06/2017 - 06:59

The real answer is pretty complex. I suggest you ask on the energyplus forum and read posts Jim Dirks. Essentially, you are entering rating condition operating point values that act together with the normalized performance curves of the dx machine only. The ARI ratings are for the entire machine meaning dx coil + fan + other. So for the proposed case that's no problem, you model the machine as it is, but the baseline is fictitious. Really, you need to adjust the curves so that the ARI rating results in the e+ results summary table are as those in the standard. There is no published way on how to adjust the curves to do this, as many different curves could lead to the same ARI rating values. Jim has suggested a defensible method. The other method is to model a real machine for the baseline with the required rated capacity and make sure the ARI rating values are "better" than the baseline, i.e. error on the conservitive side.

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Equipment efficiencies / DX Cooling Coil EER and COP

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