[Equest-users] Performance Curves - independent variable boundaries

[Bishop, Bill]

Hi Phil,
Good question! When a performance curve uses Raw Data Points (INPUT-TYPE = DATA), the coefficients for the curve are generated based on the data points and can be seen in the eQUEST Basic Specifications tab for the Performance Curve Properties. (You can generate the coefficients yourself mathematically, by using the LINEST Excel function for example.) Outputs for the curve will be determined even if the inputs (independent variable values) are outside the range of the raw data points. For example, a PLR of 0.2 and dT of 25F gives an EIR multiplier of 0.14 in the example curve below. The outputs could even be nonsensical if the simulation used garbage inputs. (An output of -0.2 using inputs of -1,-1.) I don't think there is a keyword that restricts the input variable values, but the OUTPUT-MIN and OUTPUT-MAX fix the output at those values rather than letting it go outside of those boundaries. Additionally, chillers have the MIN-RATIO keyword which defines the load for which the chiller will cycle on and off.

Regards,
~Bill

William Bishop, PE, BEMP, BEAP, CEM, LEED AP
Senior Energy Engineer

[Pathfinder-EA-logo-2]T: (585) 698-1956                        F: (585) 325-6005
bbishop at pathfinder-ea.com<mailto:wbishop at pathfinder-ea.com>        www.pathfinder-ea.com<http://www.pathfinder-ea.com/>
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From: Equest-users <equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org>> On Behalf Of Phil Jordan via Equest-users
Sent: Thursday, May 16, 2019 7:54 PM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] Performance Curves - independent variable boundaries

When a curve output exceeds the limits (min/max output, OUTPUT-MIN and OUTPUT-MAX keywords), eQUEST throws a CAUTION message in the SIM file, something like this:

**CAUTION**********************************************************************

             In curve: Variable Speed Drive FPLR        the dependent value

             is exceeding the limits.

             Value/Min/Max/First time:          1.004          0.100          1.000   7/21/ 8




I'm curious, what happens when the input type for a performance curve is "Raw Data Points" and during the course of the simulation one of the independent variables is outside the range of the raw data points? For example, here's a curve from the library (BDLLIB.DAT) that's defined via data points:
$LIBRARY-ENTRY SmFricW3VSD-EIR-fPLR&dT         CURVE-FIT       Sml Fric 3App    -044d2  35
$ 70/140 ton, 3F approach evap & cond; R134a extended 460V  10F superheat       -044d2  36
$ EIR = 0.182, 0.64 kW/ton, COP 5.5                                             -044d2  37
   TYPE = BI-QUADRATIC-RATIO&DT   INPUT-TYPE = DATA                             -044d2  38
   IN-RATIO = ( 1.00, 0.75, 0.50, 0.25,  $ PLR                                  -044d2  39
                1.00, 0.75, 0.50, 0.25,                                         -044d2  40
                1.00, 0.75, 0.50, 0.25,                                         -044d2  41
                1.00, 0.75, 0.50, 0.28 )                                        -044d2  42
   IN-DT    = ( 41.0, 41.0, 41.0, 41.0,  $ ECT-CHW DT                           -044d2  43
                31.0, 31.0, 31.0, 31.0,                                         -044d2  44
                26.0, 26.0, 26.0, 26.0,                                         -044d2  45
                46.0, 46.0, 46.0, 46.0  )                                       -044d2  46
   OUTPUT  = (  1.00, 0.70, 0.46, 0.27,  $ EIR ratio                            -044d2  47
                1.00, 0.66, 0.39, 0.22,                                         -044d2  48
                1.00, 0.65, 0.38, 0.19,                                         -044d2  49
                1.00, 0.72, 0.50, 0.32 )  ..                                    -044d2  50

In the data points, the minimum PLR boundary for the curve is 0.25 - what happens if during the simulation the PLR is 0.20? Does eQUEST use the curve output regardless (and is a CAUTION generated), or is the output at the minimum independent variable used?

Thanks,

Phil Jordan

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