[Equest-users] FW: Performance (curve) anxiety

[Hall, Brendan]

Bill,

If you have enough data points you should be able to generate similar curves in excel using the LINEST command. It spits out the same trendline coefficients that you would get if you graph data then add a trendline.

It's set up like this :

=LINEST(y-values,x-values,true,true)

This will spit out the m and b in y=mx+b.

Cubic looks like this

=LINEST(y-values,x-values^{1,2,3),true,true)

This will give you y=ax^3+bx^2+cx+d

You can also use it to do bi-quadratic, which looks like this:

=linest(y-values,x1-values^{0,0,1,2)*x2-values^{1,2,0,0),true,true)

The form here is : y = a*x1+b*x1^2+c*x2+d*x2^2+e

If you want to add a x1*x2 term you change the x value definition to : x1-values^{0,0,1,1,2)*x2-values^{1,2,1,0,0).

I think it's the same idea for bi-linear but I haven't tried it.

I was looking into how to do this a couple weeks ago and there is a decent amount of info on excel msg boards on how to generate complex regressions. Also, it has to be entered as a array, and the 2nd true statement allows it to spit out statistics about the curve fit so you can check the R2 value.

Hope that helps.



Brendan Hall,  PE, LEED AP BD+C
Engineer, Mechanical
karpinski
ENGINEERING
3135 Euclid Avenue
Cleveland, OH  44115
P  216.391.3700 x 3111
E  bhall at karpinskieng.com<mailto:bhall at karpinskieng.com>
W www.karpinskieng.com<http://www.karpinskieng.com/>



From: equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org> [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Bishop, Bill
Sent: Tuesday, March 05, 2013 4:43 PM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] Performance (curve) anxiety

Performance curves are defined by an INPUT-TYPE of COEFFICIENTS or DATA. I am creating several performance curves based on manufacturer data points, but would like to define them with COEFFICIENTS to save space in the input file.
Can someone walk me through a method to determine coefficients in Excel, or using another add-in or program, for the following CURVE-FIT TYPEs?
                TYPE             = BI-LINEAR-T
                 TYPE             = BI-QUADRATIC-T
                 TYPE             = CUBIC

Yes, eQUEST generates the coefficients when you enter data points, but I see no way to copy them to then turn around and define the curve using the coefficients.

Thanks,
Bill

[Senior Energy Engineer 28Jun2012]<mailto:wbishop at pathfinder-ea.com>

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