Psychrometric Chart Calculator Excel Online

=1.006*B3 + B7*(2501 + 1.86*B3) Cell B9:

| Property | Symbol | Typical Units | Description | |----------|--------|---------------|-------------| | Dry‑bulb temperature | T | °C or °F | Ordinary air temperature measured by a standard thermometer | | Wet‑bulb temperature | T w | °C or °F | Temperature recorded by a thermometer with a wet wick; indicates cooling by evaporation | | Dew‑point temperature | T dp | °C or °F | Temperature at which condensation begins for a given moisture content | | Relative humidity | RH | % | Ratio of actual water vapor pressure to saturation pressure at same dry‑bulb | | Humidity ratio (mixing ratio) | W | kg water /kg dry air | Mass of water vapor per mass of dry air | | Enthalpy | h | kJ/kg dry air or Btu/lb dry air | Total heat content (sensible + latent) | | Specific volume | v | m³/kg dry air | Volume per unit mass of dry air | | Vapor pressure | p w | kPa or psi | Partial pressure exerted by water vapor in the mixture | Excel does not have built‑in psychrometric functions. Instead, we must implement empirical correlations from ASHRAE Handbook—Fundamentals. The most important is the saturation vapor pressure over liquid water (Hyland‑Wexler formulation, valid 0–200°C):

For (pressure in kPa, temperature in K):

– solved iteratively from ( p_ws(T_dp) = p_w ). psychrometric chart calculator excel

=B5 * (B4/100) Cell B7:

Start with the direct formulas (T_db, RH → all outputs). Then add inverse solving via Goal Seek. Finally, if you find yourself repeatedly computing wet‑bulb or dew point, invest an afternoon in writing VBA functions—you will never need a paper chart again. Word count: approx. 1,950

– requires iterative solution of the carrier equation: =B5 * (B4/100) Cell B7: Start with the

=$B$2*0.62198*B6/($B$2-B6) Wait – careful: ( W = 0.62198 * p_w / (P - p_w) ). So correct formula:

=0.2871*(B3+273.15)/B2 * (1+1.6078*B7) Because dew point requires solving ( p_ws(T_dp) = p_w ), use Excel’s Goal Seek or implement an inverse approximation. A decent direct approximation (for 0–60°C) is:

While printed charts are useful for quick look‑ups, they suffer from low precision, interpolation errors, and inconvenience in iterative calculations. An solves these problems by embedding the governing equations directly into a spreadsheet, allowing rapid, accurate, and repeatable analysis. Word count: approx

This write‑up explains the science behind psychrometric calculations, the mathematical formulas required, step‑by‑step construction of an Excel calculator, practical applications, and advanced automation techniques. Before building the calculator, we must define the key properties of moist air, treating it as a mixture of dry air and water vapor.

[ p_ws = 0.61094 \cdot \exp\left( \frac17.625 \cdot T_dbT_db + 243.04 \right) ] where ( T_db ) is in °C, result in kPa. 1. Humidity ratio from vapor pressure