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A Python 3 library to make psychrometric charts and overlay information on them.

Project description

It implements a useful collection of psychrometric equations for moisture and humid air calculations, and the generation of beautiful and high customizable psychrometric charts in SVG with matplotlib.

Calculations are made by implementing experimental equations extracted from recognized sources, such as the 2009 ASHRAE Handbook—Fundamentals (SI).


Clone it from Github if you want to run the tests, or simply:

pip install psychrochart


  • SI units (with temperatures in celsius for better readability).
  • Easy style customization with a JSON template (colors, line styles and line widths).
  • Psychrometric charts within temperature and humidity ratio ranges, for any pressure, with:
    • Saturation line
    • Constant RH lines
    • Constant enthalpy lines
    • Constant wet-bulb temperature lines
    • Constant specific volume lines
    • Constant dry-bulb temperature lines (internal orthogonal grid, vertical)
    • Constant humidity ratio lines (internal orthogonal grid, horizontal)
  • Plot legend for each family of lines
  • Specify labels for each family of lines
  • Overlay points and zones
  • Export SVG files
  • Tested against example tables from
  • ~100 % code coverage.

The ranges of temperature, humidity and pressure where this library should provide good results are within the normal environments for people to live in. Don’t expect right results if doing other type of thermodynamic calculations. Over saturated water vapor states are not implemented.


  • v0.1.0: Initial version.
  • v0.1.1: Minor plotting fixes, set axis position, define P with altitude_m or pressure_kpa, reuse plot removing annotations (chart.remove_annotations). Axes as internal prop, lazy plotting, save to disk helper (
  • v0.1.2: Add agg module to set that matplotlib backend.
  • v0.1.3: Add custom params for plotting styles, option to exclude first and last tick (constant_{humid/temp}_label_include_limits).
  • v0.1.4: Customize labels and its locations for families of psychrometric curves.
  • v0.1.5: Add Arrows, compatibility with the Home Assistant component psychrometrics.
  • v0.1.6: Some cleaning, better typing, flake8, added tox.ini.
  • v0.1.7: Methods to clean the plot (.close_fig()) and to remove the legend (.remove_legend()).
  • v0.1.8: Memleak with savefig.
  • v0.1.10: Fix plot limits, do not use pyplot, axes are not optional.
  • v0.1.11: Add optional Axes as argument for PsychroChart.plot.
  • v0.1.12: Add empiric equation for wet bulb temperature (@ZhukovGreen contribution).
  • v0.2.0: Hide output in verbose mode, better convex hull zones syntax, stable.
  • v0.2.1: Make scipy an optional requirement (it’s only used for the ConvexHull zone).
  • v0.2.2: Fix initial conditions for iteration solvers.
  • v0.2.3: Handle ConvexHull exception, overlay of series of points.
  • v0.2.4: Set ASHRAE formulation for saturation_pressure_water_vapor as default. Minimal adjustments to iteration solvers for enthalpy and specific volume.
  • v0.2.5: Fix coefficient in ASHRAE formulation for dew_point_temperature.


from psychrochart.chart import PsychroChart
import matplotlib.pyplot as plt

axes = PsychroChart().plot(ax=plt.gca())


To run the tests, clone the repository and run:

py.test --cov=psychrochart -v --cov-report html

to generate the coverage reports.


MIT license, so do with it as you like ;-)

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