[Equest-users] Question on eQuest Modeling DX Cooling, with Bug?

Josh Greenfield JGreenfield at primerachicago.com
Wed Sep 15 10:11:39 PDT 2010
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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 <http://www.idfpr.com/dpr/WHO/pe.asp> , REP
<http://www.cityofchicago.org/city/en/depts/bldgs/supp_info/chicago_ener
gy_conservationcodeoverview.html> , LEED AP BD+C
<http://www.gbci.org/main-nav/professional-credentials/credentials.aspx>

Energy Services Manager
Associate Vice President
Primera Engineers, Ltd.
312.242.6392 Direct
jgreenfield at primerachicago.com
http://www.primerachicago.com <http://www.primerachicago.com/> 

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of
Guoguang Le
Sent: Tuesday, September 14, 2010 7:41 PM
To: Carol Gardner
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Question on eQuest Modeling DX Cooling, with
Bug?

 


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

Thanks for your time.

Best regards,

 

James
--- On Mon, 9/13/10, Guoguang Le <jamesle_tx at yahoo.com> wrote:

	
	From: Guoguang Le <jamesle_tx at yahoo.com>
	Subject: Re: [Equest-users] Question on eQuest Modeling DX
Cooling, with Bug?
	To: "Carol Gardner" <cmg750 at gmail.com>
	Cc: equest-users at lists.onebuilding.org
	Date: Monday, September 13, 2010, 7:35 PM

Hi Carol,

 

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.

 

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. 

 

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".)

 

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.

 

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

 

Can you help figure it out?

Best regards,

 

James

 

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

 

 

 


--- On Sun, 9/12/10, Carol Gardner <cmg750 at gmail.com> wrote:

	
	From: Carol Gardner <cmg750 at gmail.com>
	Subject: Re: [Equest-users] Question on eQuest Modeling DX
Cooling, with Bug?
	To: "Guoguang Le" <jamesle_tx at yahoo.com>
	Cc: equest-users at lists.onebuilding.org
	Date: Sunday, September 12, 2010, 9:11 PM

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

	On Sun, Sep 12, 2010 at 6:10 PM, Guoguang Le <
jamesle_tx at yahoo.com
<http://us.mc501.mail.yahoo.com/mc/compose?to=jamesle_tx@yahoo.com> >
wrote:


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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