[Equest-users] Electricity consumption by CHILLER

[Nick Caton]

Ana/Grammy:

 

Chiller modeling is a topic that took me many attempts (projects) to
fully get my arms around, so don't get discouraged if it boggles the
mind.

 

To start, remember that the reported "space cooling" end use consumption
values may include energy from components other than your chiller (heat
pumps, DX cooling...), so make sure that's not clouding your
perspective.

 

With that out of the way, you're right to first check and ensure the
loads on the loop are appropriate to what you're trying to model.  I
think you should review what CAPhour and PLR really represent...
Multiplying them should result in your hourly load, in Btuh, but if
you're multiplying your "operating chiller capacity at current
condition" (Hourly Load) by your PLR then I suspect the result would be
equal to "PLR^2/CAPhour."  I'm doubtful that's the value you were
looking for... Let me suggest two paths to account for what you're
trying to do:

 

If you are working with the library performance curves, recognize you
have a limited number of critical inputs to review/edit regarding the
behavior of the chiller itself:  Capacity (a part of CAPhour) and EIR at
the design/rated conditions, the design conditions themselves, and the
associated loop temperatures.  If any input on the chiller screens is
something you're unsure of, right-click it and read/re-read the
associated help entry.

 

If you want to delve into custom performance curves, welcome to the
rabbit hole!  This required significant personal learning and time for
me to get my arms around, I would suggest expecting the same.  I'd
suggest first getting comfortable specifying chillers using the library
curves, per above before pursuing this skillset.  

Still here?  Okay, the following 3-step program is what I wish I could
go back in time and tell myself months ago:

1.       Open the DOE2 help files to Volume 2: Dictionary > HVAC
Components > Chiller.  Read everything in the tree in order up to the
"Attachment to Chilled Water Loop" entry, and stop.  Pay special
attention to the "Chiller Energy Consumption" article and the
sub-entries describing each performance curve in that equation.  When
you're familiar enough to recount all the variables involved in that
equation you brought up below by memory, proceed to...

2.       Download the EDR design guidelines to HVAC simulation
<http://www.energydesignresources.com/Portals/0/documents/DesignGuidelin
es/EDR_DesignGuidelines_%20HVAC_Simulation.pdf> , and read the chapter
on chillers, pages 23-44 (of 65).  

a.       Re-read until you feel comfortable understanding what
information you need from your manufacturer rep/vendor.  A good rep is
always trying to be helpful, and may unintentionally provide the wrong
information and convince you both you're on solid footing.  You must
know exactly what data you do and don't need before beginning the
discussion of asking for that information.  Whether your vendor/rep can
deliver exactly what you want is something of a toss-up, but it's a
pretty slim chance if you don't know what that is yourself.

b.      The equations presented showing the math behind the coefficients
may seem insurmountable, but for context recognize the author(s) of this
document advocating to not figure out the coefficients directly...
rather to let eQuest/DOE2 do that legwork for you (the "data method").
To an extent this is something of a reference regarding what's going on
"under the hood."

3.       Read the lengthy discussion I started this week (with
illustrations) under the heading "Chiller Curves (oh boy!)."  This
hopefully also bring you full circle to understanding what the default
curves really look like, what they each individually represent, and
ultimately how they work together.  Note my discussion revolved around a
centrifugal VSD chiller, for context.  Other equipment may use curves of
a simpler format.

 

*If a "bi-quadratic equation" sounds like something that makes the warp
drives work on the Star Ship Enterprise, stop for a second and review
the math - it's not that crazy.  You might want to skip ahead to see to
those visualizations I provided, or even build your own in excel.  

 

Best of luck!

 

~Nick

 

 

NICK CATON, E.I.T.

PROJECT ENGINEER

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

Check out our new web-site @ www.smithboucher.com 

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Grammy
Sent: Friday, November 05, 2010 6:17 AM
To: Ana N.
Cc: equest-users
Subject: Re: [Equest-users] Electricity consumption by CHILLER

 

I am also confusing this problem, and I strongly recommend you to read
the DOE-2 engineering manual, verison 2.1A, and DOE-2.2 volume 4, which
can be downloaded from eQuest web site.

 

On page V.35 - V.38, engineering manual, it introduces the electric
calculation of chiller, and on page 265, volume4, it introduces the
chiller variable list number, you can export the hourly data in eQuest
and calculated by hand. I am lost at this step. As i know at this place,
there is something you need to notice, the unit of assign loading (1)
shall be BTU, and electric demand (12) may be kW, then I still can't get
the right number, if you get it, please let me know how.

 

On Fri, Nov 5, 2010 at 8:04 AM, Ana N. <ananeddav at hotmail.com> wrote:

 
I am trying to calculate/estimate the electricity consumption by a
chiller based on hourly outputs. 
 
First, I plugged the cooling coil load on loop and corrected EIR in the
the equitation 
 Elec= CAP hour* EIR*EIR(t1,t2)*EIR(PLR,dT)/3413 Btu/kW
 
but the calculated annual electricity consumption was not  even close to
the numbers reported under Space Cooling Enduse.
 
Then, I used PLR and operating chiller capacity at current condition to
calculate CAP hour (instead of using the cooling coil load on loop), but
calculated numbers did not make any sense.
 
Has anyone done similar calculations? I am sure I am missing something
very simple here, but what?
 
Any suggestions are very appreciated
 
 
Ana
 

 

 


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