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Nicol Graph Generator

Fill in the data and choose your styling below in order to create a graph.

What is a “Nicol Graph?”

In his paper Comfortable indoor temperatures related to the outdoor temperature (1978), Humphreys demonstrated a clear, approximately linear relationship between the temperatures which the occupants of free-running (unheated or cooled) buildings found comfortable and the mean outdoor temperature at the time. The equation of the straight line is

Tc = 13.8 + 0.53(±0.02)To
Equation 1

This means that for a free-running building the indoor temperature for comfort (Tc) increases about half a degree for every degree rise in the outdoor temperature (To).

This equation can be used to predict a likely value for the comfort temperature if the mean outdoor temperature is known. The monthly mean of the outdoor temperature for any given place may be known but a better way to visualise the relationship between indoor and outdoor temperature is to use the monthly mean of the maximum and minimum daily temperature. These are measurements taken in many places and have also been found to give a better estimate of the mean daily temperature for our purposes.

Calculating a Nicol Graph

Using this approach, it is possible to plot for each month of the year

Other monthly values of interest can also be added such as the number of hours of sunshine or humidity.

Uses of the Nicol Graph

The Nicol Graph is not intended to be a precise method for predicting the exact comfort temperature from the outdoor climate, but it will give a reliable idea of what temperature people in a particular climate are likely to find acceptable. This acceptable temperature can then be linked to the type of buildings which will be best used in these circumstances. Looking at the difference between the acceptable temperature and the likely indoor conditions given the characteristics of the buildings and the adaptive opportunities available.

Thus, a building where the acceptable temperature is much below the acceptable indoor temperature will need to consider whether the availability and use of solar heating will be sufficient or whether heating will be needed. In the opposite circumstances a building in a climate which is likely to give rise to overheating, careful consideration may be needed of the use of shading and the availability of air movement from windows or fans. The Graph will help building designers to fit the thermal design to the climatic circumstances

Using the Nicol Graph in Teaching: An Early Years Design Exercise

Early years teachers often use a simple house project to start students off as designers. For Eco, or Bioclimatic House designs that link the indoor environment to the climate outside, the Nicol Graph provides a good first step to get students thinking about how occupants may relate to the changing weather around the site today, tomorrow and in the future.

Choosing locations that students are familiar with helps them to sensually understand the climate challenges involved so let them choose a site where they grew up in, live in today, or dream of living in the future. The following simple exercise might be delivered in one lesson and students then asked to make two or three Nicol Graphs for the following week.

When exhibited side by side students from different regions will see clearly how very different climates can be, opening minds to the idea that buildings may also vary greatly between locations. Working in groups may also promote more diverse design thinking.

Nicol Graph 1:

Building a dataset manually helps the numbers involved feel real, very different from the detached experience of automated numbers generated in computer games or models. The first Nicol Graph can be drawn using current monthly mean of the Maximum and Minimum temperatures to demonstrate how far the (Adaptive) Comfort temperature derives from the site climate. The greater the divergence between comfort and site temperatures over the year, the heavier and more robust the building needs to be to provide comfort indoors.

The success of a Bioclimatic house, can be measured in the amount of a day, month or year that the house can be run on local natural energy, without needing machines to keep people safe and healthy indoors. The wider the outdoor temperature range in which people can remain comfortable indoors when the building is using no energy for heating or cooling energy, is a critical factor for the energy used in, and emissions from, the building over a year.

The efficiency of domestic machines is of secondary concern as products change over time. It is the design and construction of the actual building that gives the primary climate protection in the long term, along with the Adaptive Opportunities it offers, such as shade devices and ventilation options in and around the structure. The width of the comfort temperature range is vitally important for the survival of the growing numbers of people who cannot afford to pay large energy bills.

Nicol Graph 2:

To get a handle on how much more extreme weather can be, even today, a second Nicol Graph can be drawn using the current Absolute Maximum and Minimum temperatures rather than their Means. Students may reflect on the vital need to enhance the climatic design of homes today to keep people safe indoors in increasingly unpredictable weather.

Nicol Graph 3:

More advanced students might source future predicted climate data files for perhaps 2030, 2050, 2080 or 2100 and draw Nicol Graphs for chosen future year(s) to visually reinforce to them the scale of the future design challenges at their own site. The widening gap between current indoor Adaptive Comfort temperatures and future outdoor conditions raises questions around the extent of necessary future adaptions and how they may be achieved.

The Adaptive Comfort Principle - building Resilience for the Future.

The Adaptive Principle raises important questions that can help students think about the future. If people live in buildings which are adapted to those temperatures they normally occupy in them, what happens when those temperatures change? Will their buildings still provide safe and comfortable temperatures in a different future?

People will try to Adapt.

But how far can they adapt? Exhibiting Nicol Graphs and bio-climatic house designs for different climates beside each other in class can provide valuable insights into how different cultures design for widely different climates. In clear view will be a huge range of climate-sensitive adaptive opportunities, including buildings features and furniture, and occupant attitudes and behaviours that adapted populations adopt to become - and stay - cooler or warmer, in different climates.

The importance of Vernacular role model buildings.

A quick way to get students to think about how they might enhance their own site design strategies for future weather is to identify a current climate that loosely resembles the future climate at their site for a particular time horizon. Designs for a chosen future climate can be guided and inspired by buildings in existing analogous climates. Arups did just this for the 2080 London climate after finding it may be similar to the climate of Marseilles in 1990 (Figs 1 and 2).

A Nicol Graph is a rather crude tool

but useful for thinking about design for the future

Figure 1 (top) Figure 1 (bottom)
Figure 1. Daily Temperature ranges in the CIBSE London Design Summer Year for the 1980s (upper panel) and the ‘morphed’ ranges for the 2050s under the UKCIP02 Medium-High emissions scenario (lower panel). From Beating The Heat, produced by Arups (2005) available on:

Figure 2;
Figure 2. Comparison of predicted average temperatures in 2080s London under the high emissions scenarios with those in Marseille in 1960-90 (Source: Beating the Heat, 2005). This comparison allows designers from different cultures and climates to expand their own repertoires of climatic design features and adaptive opportunities. If the two Adaptive Comfort lines for the two climate data sets were placed on the graph as well the scale of the necessary cultural and behavioural adaptation challenges would also become clearer.

Further References:

For more interested designers and Masters student a good guide to Thermal Comfort is:

Nicol, F., M. Humphreys and S. Roaf (2012). Adaptive Thermal Comfort: Principals and Practice, London: Earthscan/Routledge. ISBN 978-0-415-69159-8.

For comfort researchers and PhD students see:

Humphreys. M., F. Nicol and S. Roaf (2015). Adaptive Thermal Comfort: Foundations and Analysis, London: Earthscan/Routledge. ISBN ISBN: 978-0415691611.

Changes to the values in this table will be reflected directly in the graph above.

Graph Title:

Please note that relative humidity is not yet implemented on the chart

Grasshopper Code

Abraham Yezioro (Technion - Israel Institute of Technology) has kindly developed and made available Grasshopper code that can take EPW weather files, calculates the comfort temperature and export all necessary data to excel to create a nice Nicol graph.


This tool is still very much a work in progress. Please report issues, or send any suggestions you might have to

Copyright ©2021 William Finlayson