Free Bioclimatic Chart Generator (Givoni and Olgyay)

A bioclimatic chart shows how far each month of a climate sits from comfort, and which passive strategies could close the gap. This bioclimatic chart generator draws every month as a line from the cool morning to the warm afternoon, on the Givoni building bioclimatic chart or on the Olgyay chart, and tells you how much of each line falls in each strategy zone. Load the climate from NASA POWER, open an EPW weather file or type your own monthly values; the chart is calculated in your browser, and an EPW file is read on your device, never uploaded.

How to use this bioclimatic chart generator

1. Set the site. Pick one of the cities in the list, or type the latitude and longitude. South and west are negative. If you chose a place in the wind rose or climate graph tool on this site more recently, the generator opens on that place.
2. Load the climate. With NASA POWER selected, press Load climate data. One click fetches the daily temperatures for 2001 to 2025 and the monthly climatology for that point. You can also choose EPW weather file, or Type monthly values and fill in four numbers per month: the mean daily maximum, the relative humidity at the maximum, the mean daily minimum and the humidity at the minimum.
3. Pick the chart. Choose the Givoni building bioclimatic chart or the Olgyay bioclimatic chart, and °C or °F. For the Givoni chart you can also set the chart pressure: sea level (101.325 kPa) or the site elevation.
4. Read the shares. Under the chart you get the share of the year that falls in each zone. The table below lists the strategies each month’s line crosses, largest share first.
5. Export. PNG is drawn at twice the export width, SVG stays sharp on a presentation board, and CSV gives you the month values, the humidity ratio at each end of the line and the share in every zone. You can export in light or dark colours, or print the tool on its own.

Two bioclimatic charts, and what separates them

The Olgyay chart comes from Victor Olgyay’s Design with Climate (1963). It plots outdoor conditions, relative humidity across the bottom and dry bulb temperature up the side, against a comfort zone, and shows what is needed to get back to it: sun when it is too cool, wind when it is too warm.

Baruch Givoni’s building bioclimatic chart, first published in 1969 and revised in 1992, works on a psychrometric chart instead: dry bulb temperature along the bottom, humidity ratio in grams of water per kilogram of dry air up the side, with the relative humidity curves drawn across. Its zones are not about the body outdoors but about the building: how far natural ventilation, thermal mass, evaporative cooling or passive solar heating can bring the indoor climate back to comfort when the outdoor air is not.

For building design the Givoni chart is usually the more useful, because its zones name a design move.

How each month becomes a line

A single average hides the swing between night and day, so the generator follows Givoni’s method and draws each month as a line between two points. One end is the mean daily maximum with the humidity at that time of day. The other end is the mean daily minimum with the humidity at that time. In most climates the warm end is also the dry end, because the same amount of water vapour gives a lower relative humidity in warmer air.

Where the humidity comes from depends on the data source.

• NASA POWER: the maximum and minimum are the monthly means of the daily 2001 to 2025 series. The humidity comes from the hourly mean day of each month in the climatology: the vapour pressure of the warmest hour is kept and carried to the mean daily maximum, and the same is done for the coldest hour and the minimum.
• EPW file: for every day the tool finds the hour of the maximum and the hour of the minimum, takes the relative humidity at those hours and averages them over the month.
• Typed values: you enter the four numbers yourself. After loading NASA POWER or an EPW file, Copy the loaded values fills the table for you to adjust.

The Givoni zones and what each one asks of the building

The zone limits are Givoni’s 1992 values for hot and developing countries, as given by Lamberts, Dutra and Pereira in Eficiência Energética na Arquitetura (3rd edition, 2014). Each zone is numbered on the chart and in the legend.

1. Comfort zone: 18 to 29 °C, 20 to 80% relative humidity, 4 to 17 g/kg. Little more than a good envelope and shade is needed.
2. Natural ventilation: 29 to 32 °C up to 20.5 g/kg, and the humid band between 20 and 29 °C above 80% relative humidity. Air movement through the rooms is the strategy: openings on opposite sides, high and low vents, plan depths that let a breeze cross. Our guide to passive ventilation strategies covers the detail.
3. Thermal mass with night ventilation: 29 to 36 °C below 60% relative humidity. Heavy walls and floors absorb the afternoon heat, and the building is flushed with cool night air so the mass starts the next day cold. This only works where the night is clearly cooler than the day, which is why it belongs to dry climates. See thermal mass in building design.
4. Evaporative cooling: 29 to 44 °C dry bulb with a wet bulb temperature up to 24 °C. Water evaporating into dry air cools it: pools, wetted screens, evaporative coolers.
5. Humidification: 18 to 27 °C where the air is very dry, below 20% relative humidity or below 4 g/kg.
6. Thermal mass with passive solar heating: 14 to 20 °C. Sun on glazing facing the equator, stored in mass and released in the evening. A Trombe wall is the classic version.
7. Passive solar heating with insulation: 10.5 to 14 °C. Solar gain still helps, but the envelope has to hold on to it.
8. Active heating: below 10.5 °C, where passive means alone will not reach comfort.

The dashed line at 20 °C is the shading line: to the right of it, sun on the glazing is a gain you do not want. Zones 1 and 6 overlap between 18 and 20 °C, as they do in the source, so a cool spring month can be both comfortable and a candidate for solar heating.

The Olgyay chart: comfort zone, shading line and wind

The Olgyay chart in this tool uses the metric version of his comfort zone published by Katafygiotou and Serghides (2015), after Georgiadou and colleagues (1996).

• Comfort zone: 21 to 27.5 °C at 30 to 65% relative humidity.
• Acceptable comfort: the same temperatures at 20 to 30% and 65 to 78% relative humidity.
• Wind needed: 27.5 to 32 °C at 20 to 90% relative humidity, where air movement of up to 3.5 m/s restores comfort.
• Evaporative cooling: above 27.5 °C and below 20% relative humidity. No published number was found for this limit, so the chart marks it as a derived limit.
• Solar radiation needed: below the shading line at 21 °C, the lower edge of the comfort zone. Above it, shading is needed.
• Beyond wind cooling: above 32 °C, or above 90% relative humidity.

Olgyay’s original chart in degrees Fahrenheit also has a sloping upper edge and extra curves for wind, moisture and radiation. Those could not be checked against the primary source, so only the limits published as numbers are drawn.

How to read your monthly lines

The share of a zone is the share of the monthly line that lies inside it. Each line is sampled at 101 points between its two ends. Because the zones overlap, the shares in a month can add up to more than 100%: a point at 30 °C and 40% relative humidity, for instance, sits in natural ventilation, in thermal mass with night ventilation and in evaporative cooling at once. Treat overlaps as a choice of strategies, not a double count.

A long line tells you the month has a large daily range: a climate where thermal mass pays off, because the building can carry the warmth of the afternoon into the night, or the coolth of the night into the day. A short line means day and night are similar, typical of humid coasts and the tropics, where air movement does most of the work. Each end of the line is a monthly mean, so the hottest afternoons sit beyond the warm end.

Points that fall outside every zone are reported as Outside all zones. On the hot side of the Givoni chart that means no passive cooling strategy in the chart reaches comfort and mechanical cooling is needed. On the Olgyay chart, very hot or very humid points fall in the Beyond wind cooling zone instead.

From the chart to the building

The chart tells you which strategies the climate rewards; the next step is the geometry. The sun path diagram generator shows when the sun reaches the glazing you want to heat or shade, and the wind rose generator shows whether there is a breeze to use for ventilation, from which direction and in which season. For the monthly temperature and rainfall picture that usually opens a climate analysis sheet, use the climate graph generator.

A hot dry climate typically shows summer lines running into thermal mass with night ventilation and evaporative cooling: heavy construction, courtyards and small shaded openings. A warm humid climate shows short lines high on the chart, in natural ventilation: light construction, deep shade and plans that let the wind through. A temperate or cold climate shows most of the year left of the shading line, in the solar heating zones.

How the calculation works, and how it was checked

The psychrometric chart is drawn with the equations in the ASHRAE Handbook Fundamentals (2017), chapter 1: the Hyland and Wexler saturation vapour pressure over ice and over water, the humidity ratio, the wet bulb temperature and the standard atmosphere pressure for a given elevation. When you choose site elevation, the elevation comes from the NASA POWER reply or from the EPW header; for typed values the chart stays at sea level. Zone boundaries are sampled in 0.1 °C steps, so the humidity and wet bulb limits stay curved.

The psychrometric functions were checked against PsychroLib 2.5 (Meyer and Thevenard, 2019). Saturation vapour pressure agreed to within 0.01% at 14 temperatures, the humidity ratio to within 0.0000001 kg/kg and the wet bulb temperature to within 0.01 K in ten test cases each.

What this bioclimatic chart does not do

It describes the outdoor climate, not the comfort inside a particular building, which depends on glazing, mass, insulation, ventilation and use and needs a thermal simulation. The chart is for early design: it tells you which strategies are worth testing.

Only zones with published numeric limits are drawn. The thermal mass for cooling zone, which the source gives only as a figure, is left out, and no air conditioning zone is drawn: hot points outside every passive zone are simply reported as outside all zones.

NASA POWER values are grid averages of roughly half a degree, not station measurements. If you have a better local source, load an EPW file from climate.onebuilding.org or type the station values.

Frequently asked questions

What is the difference between the Givoni and the Olgyay chart?

The Olgyay chart plots outdoor temperature against relative humidity around a comfort zone, with sun and wind as the corrections. The Givoni chart plots the same months on a psychrometric chart and adds zones for building strategies such as natural ventilation, thermal mass and passive solar heating.

Which comfort limits does the tool use?

On the Givoni chart, Givoni’s 1992 limits for hot and developing countries: 18 to 29 °C and 20 to 80% relative humidity, between 4 and 17 g/kg. On the Olgyay chart, 21 to 27.5 °C and 30 to 65% relative humidity. The source of each chart is printed under it.

Where does the humidity at the daily maximum come from?

From the NASA POWER hourly mean day of each month, from the hour of each day’s maximum in an EPW file, or from the number you type. The method section above explains each case.

Why is there no air conditioning zone?

The source gives no separate numeric limit for it. Hot points outside every passive cooling zone, beyond 44 °C dry bulb or 24 °C wet bulb on the Givoni chart, are reported as outside all zones: that is where air conditioning is needed.

Can I enter my own station data?

Yes. Choose Type monthly values and fill in, for each month, the mean daily maximum, the humidity at the maximum, the mean daily minimum and the humidity at the minimum.

Is this a thermal comfort calculator for my building?

No. It is a climate screening chart that shows which passive strategies suit the site. Indoor comfort in a specific design needs a simulation.