Plant Model - Environment

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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... (Independent Default Values)
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; [math]\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} }[/math] 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	Air density is a function of elevation, and the fitted polynomial equation is as follows: [math]\displaystyle{ AirDensity = 1.224805469 - 0.116626159e^{-3} \times Elevation + 0.003798009e^{-6} \times Elevation^2 }[/math]
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

Discussion Page Air in Modelling

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

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)