To all,

I have two energy models on DX cooling for a same building, one is with air cooled and another with evaporation cooling. The EER is 9.9 for air cooled condenser and? 11 for evaporation cooled condenser. The final result I got is that it is the?low cost to run air cooled condenser DX with EER 9.9 than evaporation cooled condenser DX with EER 11. I am wondering whether eQuest has bug or not. Anyone could figure it out?

Best regards,

James

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Not likely. Send a copy of your .inp and .pd2 files for help.

Carol

Hi Carol,

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I have attached two inp files, one for Air cooled condenser model with EER 9.9 and another one for Evap Cooled condenser with EER 11.

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I created these files?with eQuest Wizard mode. If you?move forward to?detailed mode, you will find "Cooling Electric Input Ratio" is 0.2911 btu/btu in EER 9.9 model and 0.2580 btu/btu in EER 11 model.

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If you run simulation, the result for EER 9.9 air cooled model is $242,752 and for evap Cooled model is $243,127. (I did not change the data on "Cooling Electric Input Ratio".)

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If I change the data in the field of "Cooling Electric Input Ratio" as 0.3444 for EER 9.9 air cooled model and 0.3100 for EER 11 evap cooled model. The result is $245,342 for EER 11 Evap cooled model and $244,726 for EER 9.9 Air Cooled model.

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The conclusion is EER 11 evap cooled model is worse than EER 9.9 air cooled model.

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Can?you help figure it out?

Best regards,

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James

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I believe that there are many Guru in the web. Thanks for your time!

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Carol, I attched files for your review. If it is true, then eQuest has some bugs.

Thanks for your time.

Best regards,

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James

James,

I noticed you didn't mention where this project is at. I would imagine that the designer knows that the evaporative coolers are really most effective in dry climates. If it is in a humid climate, the improved EER of the evaporative cooler may make no difference. Just a thought!

Jeff Seger EI

I seem to remember running into this before myself. I would check the

default curves for the DX vs. evaporative cooling. I think eQUEST assumes

a much worse partial-load performance for the evaporative curve.

Nathan Miller, PE, LEEDRAP

While I can not necessarily tell you the reason "why" you are getting

these results, I can at least point out to the specific areas as to

"how" you are getting these results and hopefully someone else can chime

in and give their opinion...

If you create hourly blocks for one of the systems in each of the models

(9.9 EER air-cooled & 11.0 EER evap-cooled), you'll see that the hourly

"Operating EIR" is higher for most every hour (except for 78 hours near

max cooling design day) of the year for the evap-cooled model. This

eQUEST value for "Operating EIR" is formally the value "Operating EIR

(COOLING-EIR*EIRM1*EIRM2) (Btu/Btu)" in the hourly result series options

and it is calculated via multiplying the ARI inputted EIR for each

cooling type and then is multiplied by the temperature correction factor

and part-load correction factor for each hour of the year...

The 9.9 EER (0.2911 EIR) and the 11.0 (0.2580 EIR) models have very

similar part-load correction factors for each hour of the year as they

both use the same DX part load ratio performance curve (the difference

is how capacity is calculated)...it's the temperature correction factor

where the values differ greatly.

The temperature correction factor for the 11.0 evap-cooled model is

higher by about 0.25 for each hour of the year, therefore when

multiplying this value times the ARI EIR value and the part-load

correction factor, the lower EER air-cooled operating EIR will get

reduced significantly due to a low temperature correction factor, while

the higher EER evap-cooled operating EIR will only be reduced a bit due

to a high temperature correction factor.

Example for June 7th @ 7am:

Air-Cooled Temp Correction Factor = 0.76158

Air-Cooled Part Load Correction Factor = 0.69831

Air-cooled Cooling-EIR = 0.2911

Air-Cooled Operating EIR (COOLING-EIR*EIRM1*EIRM2) = 0.15481

Evap-Cooled Temp Correction Factor = 1.00124

Evap-Cooled Part Load Correction Factor = 0.80601

Evap-cooled Cooling-EIR = 0.2580

Evap-Cooled Operating EIR (COOLING-EIR*EIRM1*EIRM2) = 0.20823

The temperature correction factor for air-cooled systems is a factor of

entering (mixed-air) wet bulb air temperature and outdoor dry bulb

temperature.

The temperature correction factor for evap-cooled systems is a factor of

entering (mixed-air) web bulb air temperature and outdoor wet bulb

temperature.

Also, on the 'Cooling' tab -> 'Capacity Curves' tab of each system,

there is an input for "Min temp used in cooling curves"...for

air-cooled, the wizard sets this at 70 deg F, while for evap-cooled, the

wizard sets this at 50 deg F...this means that the temperature

correction factor is a constant value for anything below those

values...0.76158 for air-cooled and 1.00178 for evap-cooled, and for a

building such as this example building where there is a significant

amount of winter cooling, this makes a large impression on the outcome

energy results.

Josh Greenfield, PE , REP

, LEED AP BD+C