Plant Model 9.3 - Environment
Navigation: View Commands Summary 9.3 -> Plant Model 9.3 -> Plant Model - Environment
This page is for SysCAD 9.3 Build 136 only. For SysCAD 9.3 Build 137 or later, please see Plant Model - 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 | 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; [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 | 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. |