# Plant Model - Environment

Navigation: User Guide ➔ View ➔ Plant Model ➔ Environment

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

This page is for Build 137 or later. For Build 136, please see Plant Model 9.3 - Environment.

## 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 / Options Description / Calculated Variables / Options

### Project Configuration Temperature & Pressure

(NOTE: The temperature and pressure values can only be changed via the Project Configuration (cfg File) 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°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 US Std Atmosphere Calculation

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 Ambient Dry Air Density: 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.
Latitude Input The latitude for the location of the Plant.
EvaporationRate Input The average evaporation rate for the location of the Plant.
RainfallRate Input The average rainfall rate for the location of the Plant.
ResetToDefaults Button Reset the Environment settings to defaults. Does not change Air composition.
Air...
List of Gas Species ... Input Define the environmental air composition on a mass basis.
This composition is used for the Feeder Operation - PlantModel Air
DryAir...
Composition User Input Allows user input of dry air composition on mass or molar basis.
Non-Reactive Air Dry air is defined as species Air(g), which must be included in the Species Database.
Standard Air Dry air per the Standard Air composition, see below for more details. N2(g) and O2(g) are required and will give a warning if not present in the species database.
N2 O2 (etc.) Various options for limiting the list of Standard Air species.
E.g. N2 O2 CO2 will only include N2(g), O2(g) and CO2(g), even if other Standard Air species are present in the species database.
Definition Mass Frac Available if Composition is User Input. Dry air composition defined on mass fraction basis (MF).
Mole Frac Available if Composition is User Input. Dry air composition defined on mole fraction basis (MlF). Equivalent to volume fraction for ideal gas.
MissingSpecies Display List of missing required species based on Composition selection and current Species Database.
AtmosCO2 Input Molar (volume) fraction of atmospheric CO2 (max 1%). Input field required as this value changes with time and affects proportion of other species.
Current default value taken from NOAA Global Monitoring Laboratory for Dec 2021[2].
Default Set Composition
(Button)
Available if Composition is User Input. Sets user-input values to composition based on other Composition options. Only options with the required species available are shown in the droplist.
List of Gas Species ... Input / Display Environmental dry air composition on a mass (MF) or molar (MlF) basis. Input only if Composition is User Input. DryAir will always have H2O(g) as zero.
This composition is used for the Feeder Operation - PlantModel DryAir

## Standard Air

The standard dry air composition is taken from NIST CIPM-2007[1], including all species with a molar fraction $\displaystyle{ \gt 0.1 \times 10^{-6} }$:

The following steps are taken to balance these values:

1. CO2(g) is overwritten and fixed (from AtmosCO2 input).
2. Mole fraction list is normalised, with all other species maintaining the same relative proportions.
3. Any missing or excluded species are rolled into N2(g) (molar basis).

Note: If any required species (e.g. N2(g) or O2(g)) are not present, a warning will show and the missing species will be listed. The calculated composition will show available species in their relative proportions and will likely lead to unexpected results.

## References

1. A., Picard, R.S., Davis, M., Gläser and K., Fujii (2008), Revised formula for the density of moist air (CIPM-2007), Metrologia 45 (2008) 149–155 doi:10.1088/0026-1394/45/2/004, pg 151 Table 1
2. "Trends in Atmospheric Carbon Dioxide" Global Monitoring Laboratory, National Oceanic & Atmospheric Administration, U.S. Department of Commerce (Accessed December 2021)