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Re: [EnergyPlus_Support] Performance curve for the chiller


And a colleague reminded me to add some cautions:

1.  There must be an adequate range of data points to achieve a valid fit.  
Extrapolation of a bi-quadratic is usually invalid, so the range of 
temperatures for both variables must be adequately represented in the data.  
And there must be sufficient points within the range to define the appropriate 
shape.

2.  At nominal conditions, the curve value must be exact.  For example, a 
chiller eir-ft curve should be 1.0 at the user-specified design water 
temperatures.  It is often the case that the resulting curve coefficients may 
produce a result which is not exactly 1.0 at the design conditions.  If it is a 
very small error, it may be sufficient to simply adjust the constant 
coefficient and shift the entire curve.  If it is more significant, it may be 
necesssary to pull the curve toward the design point by adding duplicating the 
data points at and near the design point to give them more weight.

3.  Regardless of the method used to obtain the coefficients, it is important 
to evalute and plot the curve values over a range of input conditions to make 
sure the curve fit makes sense.  Curves which cross each other or curve down 
and then up are probably invalid.

Mike


On 22 Feb 2005, at 18:28, Donald Fast wrote:

> 
> (Sorry for the strange original message as it was mistakenly sent in html)
> 
> There are also many add-ins for Excel to perform more complex curve fits.
> Here are a few of the results from a google of "excel curve fit". Both 
> of these provide links to further tools. I have one at work, but forget 
> which it is as it does not get used lots.
> 
> Microsoft *Excel* Add-in to Interpolate, Cubic Spline, and *Curve* *Fit* 
> <http://www.ozgrid.com/Excel/excel-interpolate-cubic-curve-fit.htm>
> A free collection of functions which extends the capabilities of 
> Microsoft *Excel*; developed primarily to facilitate interpolation of 
> 3-dimensional and *...*
> www.ozgrid.com/Excel/ *excel*-interpolate-cubic-*curve*-*fit*.htm - 25k 
> - Cached 
> <http://66.102.7.104/search?q=cache:n-LCByZRV6cJ:www.ozgrid.com/Excel/excel-inte
> rpolate-cubic-curve-fit.htm+excel+curve+fit&hl=en&client=firefox-a> - Similar
> pages
> <http://www.google.ca/search?hl=en&lr=&client=firefox-a&rls=org.mozilla:en-US:of
> ficial&q=related:www.ozgrid.com/Excel/excel-interpolate-cubic-curve-fit.htm> 
> 
> 
> <http://www.idbs.com/xlfit4/>
> Mathtools.net : *Excel*/Fitting and Interpolation 
> <http://www.mathtools.net/Excel/Fitting_and_Interpolation/>
> *...* Interpolate, Cubic Spline, and *Curve* *Fit* for MS *Excel* - 
> XlXtrFun.xll, Update Link / Bad Link? Three Dimensional Interpolate and 
> Extrapolate Functions; *...*
> www.mathtools.net/Excel/Fitting_and_Interpolation/ - 20k - Cached 
> <http://66.102.7.104/search?q=cache:ueMIRvSRWj0J:www.mathtools.net/Excel/Fitting
> _and_Interpolation/+excel+curve+fit&hl=en&client=firefox-a> - Similar pages
> <http://www.google.ca/search?hl=en&lr=&client=firefox-a&rls=org.mozilla:en-US:of
> ficial&q=related:www.mathtools.net/Excel/Fitting_and_Interpolation/> 
> 
> 
> 
> 
> Michael J. Witte wrote:
> 
> >On 22 Feb 2005, at 9:10, wing sun lee wrote:
> >
> >  
> >
> >>I have already checked the microsoft office excel, but it can only solve the
> >>curve fit for linear and quadratic equation by the Linest() function.
> >>    
> >>
> 
> 
> 
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> 
> 
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> 
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> 
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