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Module guide

Psychrometric chart: how to read and use C4B's psychrometric chart

C4B plots every hour of a site's typical year on a psychrometric chart, for any address. This guide explains what the module shows and how to read it, with an example from Barcelona, and compares it with other psychrometric chart tools.

The psychrometric chart module

The psychrometric chart places every hour of the site's typical year by its dry-bulb temperature and humidity ratio. The chart is divided into small cells, each coloured by how many hours of the year fall into it, from a handful (blue) to 200 or more (red), with curves of relative humidity and lines of enthalpy across it. Alongside it, a table lists the properties the chart relates: dry-bulb, wet-bulb and dew point temperature, relative and absolute humidity, specific volume, enthalpy and vapour pressure.

It is on the Free plan with the nearest weather station's data, and projects can use site-specific data. Projects on paid plans add Passive Design Strategies for Indoor Environments, which counts the share of hours each of seven strategies covers, by the Givoni-Milne or Szokolay method; the chart with the strategy zones drawn on it is in the Designer module on the Technical and Enterprise plans.

How to use it

  1. Search for an address or click on the map, or open a project.
  2. Choose the Energy data tab and open the Psychrometric Chart.
  3. In a project, switch at the top between the weather station's data and the site-specific data.
  4. Hover over a cell to see its number of hours, its dry-bulb temperature and its humidity ratio.
  5. In a project on a paid plan, open Passive Design Strategies for Indoor Environments in the Design direction tab to see which strategies extend comfort.

How to read it

The axes

Dry-bulb temperature runs along the bottom, from −20 to 50 °C, and the humidity ratio up the right-hand side, in kg of water per kg of dry air: the further right a point, the warmer the air; the higher, the more water it holds.

The curves: relative humidity

The upper curve is saturation, 100% relative humidity: air cannot hold more water, so no hour lies above it. The curves below it are lower relative humidities in steps of 10%, and an hour's relative humidity is read from the curves it lies between.

The diagonals: enthalpy

The straight diagonal lines are enthalpy, the air's total heat content in kJ/kg. Along one of them the air trades temperature for moisture at the same heat content, which is the path evaporative cooling follows.

The cells and their colours

Each cell counts the hours of the year that fall into it, coloured from a handful (blue) to 200 or more (red); the legend under the chart in the module gives the scale. Where the cells cluster are the conditions the site spends most of its time in; areas left blank are conditions it never reaches.

The table

The table names the properties the chart relates and their units: dry-bulb, wet-bulb and dew point temperature in °C (°F), relative humidity in %, absolute humidity in g/m³, specific volume in m³/kg, enthalpy in kJ/kg (Btu/lb), vapour pressure in kPa, and the hours of the grid.

Warm or cold, humid or dry

Hot, humid hours call for ventilation and solar protection; hot, dry hours suit evaporative cooling and high thermal mass with night ventilation; cold hours call for passive solar heating and internal gains.

In design

The chart is where the passive strategies start: Passive Design Strategies for Indoor Environments turns it into the share of the year's hours each strategy can make comfortable, ranked month by month.

Frequently asked questions

What is a psychrometric chart used for in architecture?

It plots air temperature against humidity. With every hour of a year's weather on it, it shows how often conditions are comfortable and which passive strategies, such as ventilation, thermal mass or passive solar heating, could extend comfort without mechanical systems.

What is a bioclimatic chart?

A temperature and humidity chart with zones for comfort and for passive design strategies. The Olgyay and Givoni bioclimatic charts are the classic examples, and many climate tools now draw similar zones on a psychrometric chart.

Is there a free online psychrometric chart?

Yes. CBE Clima Tool and EPW Insights plot a weather file's hours online for free, the CBE Thermal Comfort Tool shows comfort zones for ASHRAE 55 and EN 16798, and Andrew Marsh's Psychrometric Chart app covers both teaching and EPW plotting. C4B's Free plan includes a psychrometric chart for any address.

Can I plot my own weather file on a psychrometric chart?

Yes, in CBE Clima Tool, EPW Insights, Andrew Marsh's app, Climate Consultant and Ladybug Tools, which all read EPW files. C4B works from an address instead and does not take uploaded files.

Is the psychrometric chart on the Free plan?

Yes, with the nearest weather station's data. Projects on paid plans add site-specific data and Passive Design Strategies for Indoor Environments, with the share of hours each strategy covers.

Can I download the psychrometric chart?

Not as a separate image or data file. In projects on paid plans, the chart is part of the PDF report.

See your site's climate before design begins

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Free plan; paid plans from €59/month (cancellation takes effect after 12 billing cycles) or €599/year, with a 7-day free trial. No card required. If you add a card during the trial, the plan is charged when the trial ends; otherwise your account moves to the Free plan. See all plans.

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How C4B compares with other psychrometric chart tools

Last checked 21 October 2026

At a glance

ToolTypePriceBest for
CBE Clima ToolWeb app, open sourceFreeA free psychrometric chart of every hour in an EPW file, with filters and overlays.
CBE Thermal Comfort ToolWeb app, open sourceFreeChecking indoor thermal comfort against ASHRAE 55 or EN 16798 on a psychrometric chart.
Psychrometric Chart web appWeb appFreeTeaching and exploring psychrometrics and bioclimatic charts, with or without a weather file.
Climate ConsultantDesktop app (Windows, macOS)FreeA free psychrometric chart with 16 passive design strategy zones, in a program aimed at architects and students among others.
C4BWeb appFree plan; paid plans from €59/month (cancellation takes effect after 12 billing cycles) or €599/year, with a 7-day free trialA psychrometric chart for an address, with the share of hours each passive strategy covers.
EPW InsightsWeb app, open source (AGPL-3.0)FreeA free psychrometric chart with bioclimatic strategy overlays for any EPW file, in the browser.
Ladybug ToolsPlugins for Grasshopper (Rhino), open sourceFree and open source; requires Rhino (a commercial Rhino 8 licence is US$995 in North America)Psychrometric charts inside Rhino, for outdoor climate data or indoor simulation results.

How to choose

Be clear about the job. For climate analysis you want a chart that plots all 8,760 hours of a weather file and overlays comfort and passive design strategy zones, in the tradition of the Olgyay and Givoni bioclimatic charts. For indoor comfort you want a tool that calculates PMV or adaptive comfort to a standard such as ASHRAE 55 or EN 16798. For HVAC design you need process lines and state-point calculations.

Look at how comfort and the strategy zones are defined. Strategy zones such as fans, thermal mass or passive solar heating are simplified boundaries, so treat the share of hours they report as a guide, and check which comfort model each tool uses.

A chart is only as representative as its weather data. A station far from the site, or an old typical year, shifts the whole cloud of hours. Tools that accept your own EPW let you test a site-specific or future weather file.

Finally, consider the outputs: interactive charts for exploring, image or SVG exports for reports, or data exports for your own analysis.

CBE Clima Tool

Center for the Built Environment (CBE), UC Berkeley · Web app, open source · Free

A free psychrometric chart of every hour in an EPW file, with filters and overlays.

  • Plots all the year's weather conditions on a psychrometric chart, showing how often each condition recurs.
  • Overlays another variable, such as radiation or wind speed, and filters by date, time or value.
  • Natural ventilation potential and UTCI outdoor comfort in other tabs; SVG and CSV export.

Visit CBE Clima Tool

CBE Thermal Comfort Tool

Center for the Built Environment (CBE), UC Berkeley · Web app, open source · Free

Checking indoor thermal comfort against ASHRAE 55 or EN 16798 on a psychrometric chart.

  • PMV and adaptive comfort calculations for ASHRAE 55 and EN 16798.
  • Psychrometric charts by air or operative temperature, plus relative humidity, air speed and SET charts.
  • Open source, and described in SoftwareX (2020).

Visit CBE Thermal Comfort Tool

Psychrometric Chart web app

Dr Andrew Marsh · Web app · Free

Teaching and exploring psychrometrics and bioclimatic charts, with or without a weather file.

  • Overlays comfort metrics and psychrometric process lines, and loads EPW weather files and CSV simulation outputs.
  • Transitions between absolute and relative humidity axes to show how the Givoni and Olgyay bioclimatic charts relate.
  • Generates ASHRAE Standard 55 and EN 15251 comfort diagrams for reports.
Good to know
  • App page dated October 2018.

Visit Psychrometric Chart web app

Climate Consultant

UCLA Energy Design Tools Group (distributed by SBSE) · Desktop app (Windows, macOS) · Free

A free psychrometric chart with 16 passive design strategy zones, in a program aimed at architects and students among others.

  • Plots each of the 8,760 hours of an EPW file on the psychrometric chart.
  • Reports the share of hours in 16 design strategy zones and generates a list of design guidelines for the location.
Good to know
  • Latest Windows build listed: 6.0 Build 17 (October 2021); latest macOS build: 6.0 Build 13 (January 2020). The download page states it will not run on macOS Ventura.

Visit Climate Consultant

C4B

We make C4B

Embrace Ideas · Web app · Free plan; paid plans from €59/month (cancellation takes effect after 12 billing cycles) or €599/year, with a 7-day free trial

A psychrometric chart for an address, with the share of hours each passive strategy covers.

  • Plots every hour of the site's typical year on a psychrometric chart, including on the Free plan with weather-station data.
  • Projects on paid plans report the share of hours covered by seven passive design strategies - internal gains, passive solar heating, solar protection, natural and forced ventilation, mass cooling with night ventilation, evaporative cooling and high thermal mass; the chart with those zones drawn on it is on the Technical and Enterprise plans.
  • Projects can use site-specific reanalysis data instead of the nearest station.
Good to know
  • C4B works from a location, not an uploaded EPW, and does not export chart images or CSV/JSON data; the chart is included in the PDF report on paid plans.

EPW Insights

Ehsan Rostami · Web app, open source (AGPL-3.0) · Free

A free psychrometric chart with bioclimatic strategy overlays for any EPW file, in the browser.

  • Psychrometric chart with bioclimatic design strategy overlays.
  • Outdoor comfort (UTCI, SET, MRT) and thermal mass analyses from the same file.
  • Runs locally in the browser, with nothing uploaded.

Visit EPW Insights

Ladybug Tools

Ladybug Tools LLC · Plugins for Grasshopper (Rhino), open source · Free and open source; requires Rhino (a commercial Rhino 8 licence is US$995 in North America)

Psychrometric charts inside Rhino, for outdoor climate data or indoor simulation results.

  • The Psychrometric Chart component plots temperature and humidity from an imported EPW or from an energy simulation's indoor results.
  • Companion PMV Polygon and Adaptive Chart components for comfort zones.
Good to know
  • Runs inside Rhino and Grasshopper, so it assumes a Rhino licence and some visual-scripting experience.

Visit Ladybug Tools

Sources

We make C4B. Information about the other tools comes from their official websites and documentation, checked on 21 October 2026. Products and prices change, so check each vendor's site for the latest details. All product names belong to their respective owners.

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