SI Psychrometric Chart

This program calculates and plots psychrometric properties of moist air in SI units between -60 to 90 C

The psyhcrometric properties of air are calculated based on the ASHRAE 2021 handbook of fundamentals (SI version) with support for ASHRAE 2013 handbook of fundamentals equations. References to ASHRAE handbook are given in the m-file for easy referencing. Atmospheric pressure of 101.325kPa is considered as default which can be changed by passing the atmospheric pressure value as an input parameter.

The psychrometrics.m has the ability to calculate moist air state (Tdb, w, phi, h, v, Tdp, Twb) along with transport properties (eta, k and Cp) through input of any of the following cases of two known parameters:

1. Tdb, w; 2. Tdb, RH; 3. Tdb, h; 4. Tdb, Tdp; 5. Tdb, Twb; 6. w, RH; 7. w, h; 8. w, Tdp; 9. w, Twb; 10. RH, h; 11. RH, Tdp; 12. RH, Twb; 13. h, Tdp

A psychrometric chart can be plotted using psychplotting.m.

The program uses label.m for plotting of line labels.

The updates to the 2024 version includes:

1. Psychrometrics equations are updated to ASHRAE 2021 Psychrometrics chapter while retaining support for 2013 Psychrometrics chapter equations version.
2. Parameter input ranges are specified and extended to be in-line with ASHRAE 2021 Psychrometrics chapter equation limits.
3. Polynomial fits are used to approximate specific heats and specific volumes for air at 101.325 kPa and water based on ASHARAE RP-1485 and IAPWS formulations. The data for the fits has been provided on polynomialsfitdata.mat file and their fitting details has been provided on ASHRAE2021psychfitdata.sfit file.
4. Iterations are now based on Newton-Raphson method and need for optimization toolbox's 'fsolve' function is removed.
5. SHR scale is added to the psychrometric plot with reference point as 24 C DB and 50 % RH which can be specified as an input parameter.
6. Tdp points at specified SHR points can be obtained as an output of psychplotting function.
7. Relative humidity can be specified with both 'phi' and 'rh' keywords.
8. Moist air transport properties are added as output parameters.
9. Error reporting is improved to handle unrealistic moist air parameters.
10. Comments in psychrometrics.m are improved to enhance understanding of underlying assumptions, formulae and their use in computation and generation of psychrometric plot.
11. Examples of psychrometrics usage in HVAC&R cooling coil processes are added in example.m.