HumidAir Excel Add-In

HumidAir for Excel based on real gas formulation (32 bit & 64 bit)

For Excel 2003 / 2007 / 2010 (32 bit & 64 bit) / 2013 (32 bit & 64 bit) / 2016 (32 bit & 64 bit)

HumidAir Excel Add-In

About Humid Air Excel Add-In

The psychrometrics Excel Add-In library calculates 35 thermodynamic properties of humid (moist) air in SI and English units.

It allows 21 different combinations of input variables to be used for calculations.

Input variables that can be used are:

  • Pressure
  • Dry bulb temperature
  • Wet bulb temperature
  • Dew bulb temperature
  • Relative humidity
  • Humidity ratio
  • Enthalpy
  • Entropy
  • Volume

The library is fully integrated in Excel, and available functions can be used in the same way as any other Excel function.

Main features of the library:
  • Professional quality, industrial strength software
  • Based on the most accurate formulation (Hyland and Wexler)
  • Accurate and thoroughly tested
  • Developed in C++ for maximum speed
  • Create User Defined Functions (UDF) which use HumidAir functions
  • Call HumidAir functions from VBA (samples are included in the release version)
  • Easy to install and easy to use
  • For installation and use of the library no administrator rights required
  • After installation no computer restart required
  • One year free technical support

The following figure shows a sample spreadsheet included in the download package.

HumidAir Excel Add-In

HumidAir Excel Add-In - Sample calculations in Excel

Used Formulations

The psychrometrics libray uses the most accurate formulations of thermodynamic properties of moist air.

Formulations are based on the study performed by Hyland and Wexler, and approved by ASHRAE (American Society of Heating, Refrigeration and Air-conditioning Engineers) as documented in the 1997 ASHRAE Handbook "Fundamentals". They presented the equation of state in:

  • Formulations for the thermodynamic properties of the saturated phases of H2O from 173.15 K to 473.15 K, W. Hyland and A.Wexler, ASHRAE Transactions, 89(2A) 500-519, 1983.
  • Formulations for the thermodynamic properties of dry air from 173.15 K to 473.15 K, and of saturated moist air from 173.15 K to 372.15 K, at pressures to 5 MPa, R. W. Hyland and A. Wexler, ASHRAE Transactions, 89(2A) 520-535, 1983.

System Requirements

Operating system Windows XP / Vista / Windows 7 / Windows 8 / Windows 8.1 / Windows 10.

Excel 2003 / 2007 / 2010 (32 bit & 64 bit) / 2013 (32 bit & 64 bit) / 2016 (32 bit & 64 bit).

User privileges
Installation and use of the library requires standard user privileges or better.

Psychrometric Properties

The following thermodynamic and transport properties can be calculated with HumidAir Excel Add-In:

Calculable properties in SI or E units - HumidAir Excel Add-In v3.1
  1 Dry bulb temperature [Tdb]
  2 Wet bulb temperature [Twb]
  3 Dew point temperature [Tdp]
  4 Pressure [P]
  5 Saturation water pressure [Ps]
  6 Saturation pressure at wet bulb temperature [Pwb]
  7 Saturation pressure at dew point temperature [Pdp]
  8 Mole fraction of water [Xw]
  9 Mole fraction of air [Xa]
 10 Weight fraction of water [Ww]
 11 Weight fraction of air [Wa]
 12 Humidity ratio [W]
 13 Saturation humidity ratio [Ws]
 14 Degree of saturation [DS]
 15 Relative humidity [RH]
 16 Specific volume of dry air [Va]
 17 Specific volume of saturated ice [Vi]
 18 Specific volume of saturated water [Vw]
 19 Specific volume of saturated vapor [Vv]
 20 Specific volume of moist air [Vm]
 21 Specific density of dry air [Da]
 22 Specific density of saturated ice [Di]
 23 Specific density of saturated water [Dw]
 24 Specific density of saturated vapor [Dv]
 25 Specific density of moist air [Dm]
 26 Specific enthalpy of dry air [Ha]
 27 Specific enthalpy of saturated ice [Hi]
 28 Specific enthalpy of saturated water [Hw]
 29 Specific enthalpy of saturated vapor [Hv]
 30 Specific enthalpy of moist air [Hm]
 31 Specific entropy of dry air [Sa]
 32 Specific entropy of saturated ice [Si]
 33 Specific entropy of saturated water [Sw]
 34 Specific entropy of saturated vapor [Sv]
 35 Specific entropy of moist air [Sm]

Range of Validity

The entire set of equations used by the Humid Air application, is defined by the following temperature and pressure range:

  • 173.15 K <= T < = 473.15 K
  • 0.000001 MPa <= P < = 5 MPa

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.

Reference Point

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 the 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.


The following screenshots demonstrate how to use the library, it's a 4 step process.

1.(a) Start Excel and press the "Insert Function" toolbar button.

Insert Function toolbar button

1.(b) Alternatively, start Excel and press the "Insert Function" menu item.

Insert Function menu item

2. Select a HumidAir library (SI or English units).

Select HumidAir library

3. Select a function and press the OK button.

Select Function - HumidAir library

4. Enter input parameters and press the OK button.

Calculate HumidAir properties

NOTE: You don't have to put quotes around the property ID, they are inserted automatically.

That's it, the result will be displayed in the selected cell.


The setup program will automatically install the library in Excel.

To install the library successfully you must have at least standard user privileges on your computer.

HumidAir Excel Add-In library

For Excel 2003 / 2007 / 2010 (32 bit) / 2013 (32 bit) / 2016 (32 bit)

- Download HumidAir Excel Add-In version (3.1) - demo (32 bit)

HumidAir Excel Add-In library

For Excel 2010 (64 bit) / 2013 (64 bit) / 2016 (64 bit)

- Download HumidAir Excel Add-In version (3.1) - demo (64 bit)


For the demo version input pressure is fixed to:

  • p = 8 bar in SI Units and
  • p = 116.029 psi in English Units.

These values will be used for calculation regardless of your input value for pressure.

To further evaluate the library (at pressure p = 1 bar or p = 14.5 psi), go to our Psychrometric Calculator web application, it uses the same calculation engine.

Quick reference documents

- List of available properties in the HumidAir Excel Add-In library

- List of available functions in HumidAir Excel Add-In library

Price info

Prices subject to change without notice!

A license includes 32 bit and 64 bit version of the library.

HumidAir Excel Add-In version 3.1
1-4 licensesUSD 199.95 per copy
5-20 licensesUSD 174.95 per copy
21 > licensesUSD 149.95 per copy
Company wide licenseUSD 7995.00


Each license also includes the following:

  • One year free e-mail technical support
  • One year free minor version updates if available (for example 3.2, 3.x up to, but not including version 4.0)

If you have any questions, please don't hesitate to contact sales at:

General Information

For quick access to the HumidAir Excel Add-In, you may purchase and download our product using automated and secure online ordering system. After ordering, you will receive a notification mail with further instructions, your password (required during installation) and the retail version download location.

The Registration includes a free subscription program. Each Registered user will be receiving bug fixes and technical support for the registered version within one year.

Shipping by the postal mail is not available.

How to order

1. Internet ordering

Available ordering options (open an order form to select):

  • Credit Card (Visa®, Mastercard®, American Express®, Discover®)
  • PayPal
  • Amazon

To buy a specific number of licenses for the HumidAir Excel Add-In click the button: Open order page for the HumidAir Excel Add-In or to purchase a Company Wide License contact sales at:

2. Bank Direct Payment

If you prefer to pay for the product by "Bank Direct Payment", contact sales at: