The HumidAirWeb application calculates 35 thermodynamic properties of humid (moist) air. It allows 21 different combinations of input variables to be used for calculations.
Input variables that can be used are:
Calculation of thermodynamic properties in the application is based on the most exact formulations of thermodynamic properties of moist air currently available. These formulations are approved by ASHRAE (American Society of Heating, Refrigeration and Air-conditioning Engineers) as documented in the 1997 ASHRAE Handbook "Fundamentals". Hyland and Wexler presented the equation of state in:
The entire set of equations used by the HumidAirWeb - Psychrometric Calculator application for calculation of thermodynamic properties, is defined by the following temperature and pressure range:
Moist Air Properties Limits
The upper limit of the absolute pressure is set at 5 MPa, and the temperature is restricted to the range -100 to 200°C. However, for any given absolute pressure, the highest temperature cannot exceed that temperature at which the saturation vapor pressure equals the absolute pressure.
In other words, moist air properties are valid for any dry-bulb temperatures below or equal to the saturation temperature of water at the same given absolute pressure, above that limit saturated moist air cannot exist.
IMPORTANT:
In the used formulations for calculation of thermodynamic properties of moist air, the reference state (zero enthalpy) is set at 0 °C. On some psychrometric charts (especially in the US) the reference state (zero enthalpy) is set at 0 °F.
As a consequence, enthalpy and entropy values calculated by the library will be shifted on these charts for the difference between reference points.
Since for any process calculation only enthalpy difference (in and out of a process) is important, the reference point doesn't really matter.
If you want to reproduce enthalpy values from such charts, you should find the enthalpy difference for one point (doesn't matter which one), and then add that value for all calculated enthalpies. The same applies for entropy values.
To calculate properties, Psychrometric Calculator allows up to 21 different combinations of input variables in SI or English units:
For input pressure, always enter absolute pressure and not gauge pressure.
The following 35 thermodynamic properties can be calculated with Psychrometric Calculator:
To open a new file, do the following:
Alternatively, press the "New" toolbar button.
This will clear all currently displayed data on the forms.
To save calculated properties to your local computer, use the following steps:
The CSV Unicode format will save properly some special characters contained in the definition of units. Since CSV is just a text file you can open a saved file with any text editor, for example Notepad.
On the "Setup Pane" in the "Units" group box, set units as required. SI and English units are available.
In order to calculate properties of the moist air use the following steps:
Detailed result of a calculation is displayed in the main table, located in the lower part of the input form, and also 14 main properties are displayed in the Output Pane. Input arguments used for calculation are displayed in red.
In the Output Pane results are always inserted at the top, so you don't have to scroll to see the latest result.
Fig.1 Calculation of thermodynamic properties of moist air
To calculate sensible heat flow, latent heat flow, total heat flow and sensible heat factor, use the following steps:
The solver can handle all of the following heating and cooling processes:
Results of the calculation will be displayed in the first empty "results" column in the main pane. Depending on the input parameters heating or cooling flows will be calculated.
Before making the fourth calculation, press the "Clear results" button to clear results from the 3 available result columns in the main pane.
For each calculation, calculated inlet and outlet conditions will be displayed in the Output Pane as well. To distinguish heating / cooling results from other data, rows for heating process will be displayed in red and for cooling process in blue.
The last two columns in the Output Pane (Process and Point) provide a description of a calculated point.
In the Output Pane results are always inserted at the top, so you don't have to scroll to see the latest result.
To calculate properties of a mixing process, use the following steps:
The solver can handle mixing points in the following areas:
Results of the calculation will be displayed in the first empty "results" column in the main pane.
Before making the fourth calculation, press the "Clear results" button to clear results from the 3 available result columns in the main pane.
For each calculation, calculated inlet and outlet conditions will be displayed in the Output Pane as well. To distinguish mixing results from other data, rows with calculated values will be displayed green.
The last two columns in the Output Pane (Process and Point) provide a description of a calculated point.
In the Output Pane results are always inserted at the top, so you don't have to scroll to see the latest result.