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ElectronicEnthalpyEconomizerCurves.idf
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!===============================================================================
! ElectronicEnthalpyEconomizerCurves.idf
!
! EnergyPlus Reference Data Set for Electronic (Variable) Enthalpy Economizer limit
!
! Modification History: 01/29/2008, R. Raustad, FSEC
!
! These curves approximate the electronic (variable) enthalpy curves used
! to simulate electronic enthalpy economizer control. This control scheme
! adjusts the upper outdoor air humidity ratio based on outdoor air
! dry-bulb temperature. California Title 24 ACM 2005 lists the allowable
! economizer control strategies with curve A as one of the options.
!
! Electronic Enthalpy curves A-D are presented here.
! Curve A has the highest limit and curve D has the lowest limit.
!
! The curve objects below represent a single-point electronic enthalpy
! control curve with the minimum value of x crossing the psychrometric
! chart's saturation line and the maximum value of x crossing the
! psychrometric chart's dry-bulb temperature axis. The curves are
! evaluated at an outdoor dry-bulb temperature to provide a maximum
! operating outdoor humidity ratio for economizer operation. If the
! outdoor humidity ratio is greater than this maximum value, economizer
! operation is terminated.
!
! These curves may be used with other economizer limits to create
! multi-point economizer control (Temperature Limit, Temperature Low Limit,
! Enthalpy Limit, and Dew Point Temperature Limit).
!
! Form of the Electronic Enthalpy Curve Equation:
! K = 45.672192 - 1.1559942 * Temperature (C) - 0.144599 * Relative Humidity (%)
!
! where: K = Constant value to represent specific curve
! T = Outdoor Dry-Bulb Temperature (C)
! RH = Outdoor Relative Humidity (%)
!
! NOTE: modifying the RH multiplier (-0.144599) tends to "wag" the curvature
! at the upper relative humidities. Decreasing the multiplier "wags"
! the upper portion of the curve downward, increasing "wags" it
! upwards. Modifying the constant (K) moves the intersection of
! the curve with the Dry-Bulb Temperature axis. Increasing the constant
! moves the intersection to the left as shown in the figure, decreasing
! moves to the right. The minimum and/or maximum x boundaries in the
! curve objects below may have to be adjusted when modifying the equation.
!
! Control Curve Approximate
! Curve Constant Control Point
! K at 50% RH
! (C)
! A 12 22.9
! B 14 21.1
! C 16 19.4
! D 18 17.7
!
! ________________
! . Enthaply |
! Psychrometric . Curve |
! Chart . / |
! . . / |
! . . / | Outdoor
! . A . | Humidity
! | B . | Ratio
! | C . | (kg/kg)
! | D . |
! | . |
! |____________________________._|
! Outdoor Dry-Bulb Temperature (C)
! | |
! | |
! minimum maximum
! value value
! of of
! x x
!
! Figure - Psychrometric Chart Illustration of the Electronic
! (Variable) Enthalpy economizer limit curve objects.
! Curve output is Humidity Ratio as a function of T.
!
!
! Example Curve A:
! 12 = 45.672192 - 1.1559942 (T) - 0.144599 (RH)
!
! Step 1: Identify temperatures at incremental RH values
!
! T = (12 - 45.672192 + 0.144599 * RH) / -1.1559942
!
! RH Temp
! (%) (C)
! 0 29.128
! 10 27.877
! 20 26.627
! 30 25.376
! 40 24.125
! 50 22.874
! 60 21.623
! 70 20.372
! 80 19.121
! 90 17.871
! 100 16.620
!
! Step 2: Use psychrometric routines to identify humidity ratio at each point
!
! Humidity
! RH Temp Ratio
! (%) (C) (kg/kg)
! 0 29.128 0.00000
! 10 27.877 0.00232
! 20 26.627 0.00433
! 30 25.376 0.00605
! 40 24.125 0.00750
! 50 22.874 0.00872
! 60 21.623 0.00971
! 70 20.372 0.01051
! 80 19.121 0.01112
! 90 17.871 0.01158
! 100 16.620 0.01189
!
! Step 3: Use multiple linear regression to solve one of the following equations:
!
! Humidity Ratio = A0 + A1*Temp + A2*Temp^2 (Quadratic)
! Humidity Ratio = A0 + A1*Temp + A2*Temp^2 + A3*Temp^3 (Cubic)
!
! Step 4: Use the coefficients calculated in the multiple linear regression to create
! a cubic (or quadratic) curve object.
!
!
! The method described here was used to create the following 4 "cubic" curve objects.
!
! The objects and syntax in this dataset comply with EnergyPlus, Version 8.4.0 and above, unless otherwise noted.
! Version,
! 9.0; !- Version Identifier
Curve:Cubic,
ElectronicEnthalpyCurveA,!- Name
0.01342704, !- Coefficient1 Constant
-0.00047892, !- Coefficient2 x
0.000053352, !- Coefficient3 x**2
-0.0000018103, !- Coefficient4 x**3
16.6, !- Minimum Value of x
29.13; !- Maximum Value of x
Curve:Cubic,
ElectronicEnthalpyCurveB,!- Name
0.011529339, !- Coefficient1 Constant
-0.00032266, !- Coefficient2 x
0.000042788, !- Coefficient3 x**2
-0.000001692, !- Coefficient4 x**3
14.88, !- Minimum Value of x
27.4; !- Maximum Value of x
Curve:Cubic,
ElectronicEnthalpyCurveC,!- Name
0.010189477, !- Coefficient1 Constant
-0.000235708, !- Coefficient2 x
0.000034991, !- Coefficient3 x**2
-0.000001608, !- Coefficient4 x**3
13.16, !- Minimum Value of x
25.67; !- Maximum Value of x
Curve:Cubic,
ElectronicEnthalpyCurveD,!- Name
0.008798417, !- Coefficient1 Constant
-0.000132302, !- Coefficient2 x
0.000025932, !- Coefficient3 x**2
-0.000001494, !- Coefficient4 x**3
11.43, !- Minimum Value of x
23.94; !- Maximum Value of x