[Equest-users] FW: [eSimForums] Custom Chiller Curves

[Jeremy McClanathan]

Hello,



I have a couple more questions to add to the chiller curve conversations going on.  I posted the question to eSimForums so the spreadsheet would stay with the topic and am forwarding the question along.  Below are the questions, and here is a link to the post:

http://www.esimforums.com/equest/viewtopic.php?f=13&t=105&view=unread#unread<http://www.esimforums.com/equest/viewtopic.php?f=13&t=105&view=unread%23unread>



Thanks for any advice,



Jeremy



-----Original Message-----
From: admin at esimforums.com [mailto:admin at esimforums.com]
Sent: Friday, November 05, 2010 2:18 PM
Subject: [eSimForums] Custom Chiller Curves



New post:



Hello all,



Attached is a spreadsheet I used to gather information from a manufacturer

and create custom chiller curves using the EDR guidelines for modeling

energy efficient chillers (link to the document at the bottom of the post).

 I have been testing the curves in two models. In a test wizard model (also

attached), both curves work.  In another real model (which I can't upload)

the curves that I expected to be correct cause the chiller to create

energy.  The difference between the curves is the PLR equation.  So, I have

a few questions regarding gathering information from manufacturers and the

PLR equation.



1)

When I specify a %load for a part-load data point, does this automatically

dictate an operating capacity that a manufacturer must input into their

program?  For example, in the attached spreadsheet, I chose to ask for 90%

load with a CHWS & ECT of 42 & 78.  I take this to mean that I am asking

the manufacturer to input an operating capacity of 90% of the full load

capacity at the same CHWS & ECT’s (0.9*343=308.7 tons in the attached

spreadsheet) into their software and give me the corresponding power drawn

by the chiller.  However, in the EDR guidelines for modeling energy

efficient chillers, there is an example Manufacturer Data Request Form

which has a note in both the capacity and power columns that says “Note to

Chiller Manufacturer Rep., Please allow your program to size (don’t input

capacity and kW into your program)”.  This makes sense for the full load

capacity, but does it apply to the part load?  If so, what is the

difference between %load and part load capacity?



2)

Does there need to be a part load data point for every full load data

point?

a.

I would say yes based on page 26 of the EDR guidelines, which says “each

part-load point must have a corresponding full-load data point with

matching evaporator and temperatures.”  This seems to answer my question.

But, on page 28 of the same document in the example Manufacturer’s Data

Request Form, they do not ask for part-load points that correspond to

full-load points.  This is a bit confusing, so I would just like to

confirm.



3)

When asking for part load data from a manufacturer, does it matter which

%load I ask for at each data point corresponding to a CHWS & ECT?



4)

In the attached spreadsheet, the difference between curves on the sheet

named Curve 1 and the ones on sheet Curve 2 is the divisor in the PLR

equation (starting in cell W15).  The given PLR equation is PLR =

Qi/(Qref*CAPFT).  Curve 2 represents my interpretation of this equation

where Qref is a constant representing the capacity at the point of unity.

However, when I used this curve in a model, the chiller energy came out

negative (magically created energy instead of consuming it).  A colleague

of mine read a document that suggested that Qref in the PLR equation is a

different Qref than in the other equations and it could be interpreted as a

variable reference (which I would call Qi, not Qref).  So, we tried it and

it worked, or at least it caused the chiller to consume energy instead of

creating it.  I have a difficult time believing that Qref is a variable and

not a constant, but the fact that the curve worked with Qref as a variable

and didn’t work as a constant forces me question it.  Since then, I tried

the same curves in another model and they both work, which confused the

situation more.  Is my interpretation that Qref is a constant representing

the capacity at the point of unity correct?



For ref, the EDR guidelines I am referring to can be found at the following

link:



http://www.energydesignresources.com/Resources/Publications/DesignGuidelines/tabid/73/articleType/ArticleView/articleId/138/Design-Guidelines-HVAC-Simulation-Guidelines.aspx





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