# Plant Model 9.3 - Environment

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Navigation: View Commands Summary 9.3 -> Plant Model 9.3 -> Plant Model - Environment

FlwSolve Tab Settings Tab Project Tab RC Tab Species Tab Views Tab Soluble Tab WaterQuality Tab
Qualities Tab Environment Tab System Tab Flowsheets Tab Status Tab Statistics Tab States Tab Globals Tab

## Introduction

This tab page on the Plant Model Access Window has a number of parameters that the user may either set or read for environment settings.

To access these tags in PGM or Model Procedure (MP) files, please see Plant Model Class.

Tag (Long/Short) Input / Calc Description / Calculated Variables / Options

### Project Configuration Temperature & Pressure

(NOTE: The temperature and pressure values can only be changed via the Edit Configuration command prior to loading of project, except for the standard temperature and pressure which has been hardwired.)
NormalTemp / NormT Display Normal temperature specified in the configuration file.
NormalPress / NormP Display NormalpPressure specified in the configuration file.
StandardTemp / StdT Display Standard temperature, hard wired to 25 deg C.
StandardPress / StdP Display Standard pressure, hard wired to 101.325 kPa.
ProjectMinPress / PrjMinP Display Minimum project pressure specified in the configuration file.
ProjectMaxPress / PrjMaxP Display Maximum project pressure specified in the configuration file.
ProjectMinTemp / PrjMinT Display Minimum project temperature specified in the configuration file.
ProjectMaxTemp / PrjMaxT Display Maximum project temperature specified in the configuration file.

### Ambient and Environment Conditions

Environment...
Elevation Input Elevation above sea level, used to calculate the atmospheric pressure.
AtmPressure / P Calc Legacy Calculation (Build 134 and older) The atmospheric pressure calculated from the elevation using curve fit of the standard atmosphere data. The differences between the correlations at low altitudes between this and the new method used in Build 135 are only small.
Reference for Air Pressure and Air Density calculation: Perry's Chemical Engineers Handbook, 7th Edition, TABLE 2-236 Thermodynamic Properties of the International Standard Atmosphere.
Calculated Pressure P (kPa) = C0 + Z*(C1 + Z*C2) where:Z = height above sea level in meters, C0 = 101.325, C1 = -11.83693496e-3 and C2 = 0.479317541e-6.
Calc US Std Atmosphere Calculation This model is used in Build 135 and newer.

Ambient atmospheric pressure is calculated as a function of altitude using correlations from the 1976 US Standard Atmosphere model. The ambient pressure is calculated from;

\displaystyle{ \begin{align} \text{Absolute Pressure, }P & =101325 \left(1 - 2.255772*10^{-05}\,h \right)^{5.255876}\,\, [Pa]\\ h & = \text{Altitude above sea level} \,\,[m] \end{align} }

NB ambient pressures in weather report data have been corrected for altitude and are not the actual pressures (see environmental models for more detail).

AmbientTemp / T Input The Ambient Temperature. The ambient temperature is used by some models, e.g. Environmental Heat Exchanger - loss to Ambient
AirWetBulbTemp / AirWetBulbT Input The Ambient Wet Bulb Temperature. The ambient wet bulb temperature may be used by some models, e.g. the Surface Area (ASHRAE) method in the Evaporator sub-model.
AirDensity Calc Legacy Calculation Density of Air at the specified elevation for the standard atmosphere model which assumes a constant temperature lapse rate. Curve fit to standard atmosphere data.
Calculated Density (kg/m^3) = C0 + Z*(C1 + Z*C2) where: Z = height above sea level in meters, C0 = 1.224805469, C1 =-0.116626159e-3 and C2 = 0.003798009e-6.
Calc New Calculation Ambient Dry Air Density The Legacy calculation uses a temperature which is determined as a function of altitude. This has been replaced in the expanded environmental models with an ideal gas density calculation using the ambient atmospheric pressure and the user input ambient temperature (see environmental models for more detail).
WindSpeed Input The average wind speed
WindDirection Input The wind direction.
RelativeHumidity Input The relative humidity of air. 100% humidity = fully saturated. 0% = no water in air.
Air...
State Display Feedback information to show if gaseous components are present in the project.
species 1 Input If a gaseous species is present in the project, it will be available here to define the environmental air composition on a mass basis.