Psychrometric chart
Every hour of the site's typical year is placed on the chart 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), so the conditions the site spends most of its time in stand out at a glance.
Curves of relative humidity and lines of enthalpy run across the chart, so every cell can also be read as a humidity and a heat content. 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.
The hourly temperature analysis also compares the site against an ASHRAE-55 adaptive comfort band.
Passive design strategies for indoor environments
Projects on a paid plan measure the site against bioclimatic strategy zones and count the share of the year's hours that fall inside each one, ranked month by month. You choose the method: Givoni-Milne, whose zones are fixed shapes from the published Building Bio-Climatic Chart, or Szokolay's control potential zones, calculated from the site's own climate.
Under Givoni-Milne the seven strategies are passive solar heating, internal gains, solar protection, natural & forced ventilation, high thermal mass, mass cooling & night ventilation, and evaporative cooling.
From hours to a design direction
Szokolay's set separates thermal mass into a heating and a cooling strategy, and splits evaporative cooling into direct and indirect. The comfort zone sits alongside the strategies as the reference they are measured against, not as a strategy of its own.
Two donut charts give the numbers that matter: the share of heating hours, and of cooling hours, that the selected strategies remove from a mechanical system. C4B pre-selects the combination that removes the most while still being buildable as one design, and flags which pairs reinforce each other and which impose conditions on the building. Under Givoni-Milne it also tests the two thermal-mass strategies day by day, leaving out days whose predicted indoor peak would still fall outside comfort.
The Designer module
The Technical and Enterprise plans add a second module, Passive Design Strategies for Indoor Environments - Designer:
- The psychrometric chart with the strategy zones drawn on it.
- Every hour of the year as a heatmap, and the breakdown by season and time of day.
- A technical month-by-month hours breakdown.
- A choice of comfort definition: the method's own zone, ASHRAE 55-2023, ISO 7730 or EN 16798-1:2019.
See your site's climate before design begins
Pin any location and get climate, comfort and preliminary energy insight your whole team can read. Start with a 7-day free trial, or book a 30-minute demo.
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.
Frequently asked questions
How do I read the psychrometric chart?
Temperature runs along the bottom and humidity ratio up the right-hand side. Each coloured cell is a combination of the two, and its colour says how many hours of the year the site spends there. Follow the curved relative humidity lines to see how close the air is to saturation, and the sloping enthalpy lines to compare heat content.
What is a psychrometric chart used for in architecture?
It plots air temperature against humidity. Overlaying the hours of a climate on it shows how often conditions are comfortable and which passive strategies could extend comfort without mechanical systems.
Which passive strategies does C4B evaluate?
Under Givoni-Milne: passive solar heating, internal gains, solar protection, natural and forced ventilation, high thermal mass, mass cooling with night ventilation, and evaporative cooling. Szokolay's control potential zones drop internal gains and solar protection, separate thermal mass into a heating and a cooling strategy, and split evaporative cooling into direct and indirect. Each one comes with the share of the year's hours it covers.
Can one hour count for more than one strategy?
Yes, and it usually does. The strategy zones overlap, so a single hour can fall inside several of them and counts for each one. Under Givoni-Milne, one thermal-mass zone sits entirely inside the other. The shares should not be added together; for a single figure, read the donut charts, which count each hour once.
Is this available on the Free plan?
The psychrometric chart is available on the Free plan with weather-station data. The passive design strategies are part of design direction, in projects on the Essential and Teams plans. The Designer module is part of the Technical and Enterprise plans.
Learn the concepts
Psychrometric chart for architects
The axes and curves of the psychrometric chart, where comfort zones sit on it, and how to read a climate's hours for passive design.
Passive design strategies by climate
How bioclimatic charts link ventilation, thermal mass, evaporative cooling, internal gains and passive solar heating to the climates where they work.
Adaptive thermal comfort
ASHRAE 55 and EN 16798-1 adaptive comfort: when the method applies, the equations and limits, and how to use them in naturally ventilated design.
Climate-responsive design
The principles of climate-responsive design, and the strategies that suit hot-dry, hot-humid, temperate and cold climates, grounded in building science sources.
Related features
Köppen climate zone
Köppen-Geiger and ASHRAE 169 climate zones for any site, with a Köppen-Geiger map from 1901 to 2100 under five climate scenarios.
Preliminary energy analysis
An hourly preliminary energy balance and orientation and aspect-ratio optimization for early design.
Outdoor comfort (UTCI)
UTCI outdoor thermal comfort heatmaps by season and hour, and strategies for sun and wind exposure.