Picture: Santa Monica Pier, Santa Monica, United States. Credit: Pure Virtual (Unsplash).

The thermal sensation scale is a seven-point descriptive scale that has been used extensively in outdoor thermal comfort research. Its primitive descriptions range from cold (-3), through neutral (0) to hot (3).

The shortcoming of this scale for outdoor environments comes about because it was originally designed for indoor thermal comfort. As such it doesn’t take into account the affective state such as whether something is pleasant or unpleasant; and many of the other comfort aspects that occur in outdoor environments including changes in wind, and solar radiation.

For this reason, CLEX researchers and colleagues from the University of New South Wales, The University of Sydney and Hong Kong Polytechnic decided to develop a more complex framework to take into account these differences. To make the scale accessible to non-professionals, the researchers used a range of descriptions that kept the framework in the form of understandable daily language.

The researchers started with four descriptive characteristics – thermal sensation, humidity, wind and solar radiation. They then added two further characteristics that described the effect on the individual in these outdoor environments – thermal pleasure and thermal intensity. This expanded the single 7-point scale into a complex scale measured across six descriptive classifications.

To ensure this new six-dimensional scale functioned in an easily accessible way the researchers approached the development of the scale and proof of its accessibility over two phases.

In the first phase, they used an online thesaurus to select 76 everyday adjectives likely to be related to experiencing climate/weather conditions. They then employed 135 native English speakers and asked them to place these adjectives into each of the combined descriptive areas. They did this using three short surveys produced during winter, spring and summer. Once these descriptions were in place, the researchers moved to phase 2.

In phase 2 the researchers  recruited another set of participants and asked them in the field to match how they were feeling outside at that particular moment with the descriptions provided in phase 1. They found a match 93.4% of the time.

This showed that non-professionals were able to consistently interpret this much more nuanced and evocative multi-dimensional thermal perception scale regardless of whether they were exposed to the actual thermal environment or not. This opens the door for the use of future climate descriptions that have far more meaning to the general public than simple measures of wind speed, temperature etc and which can be used in research and or public announcements of weather conditions.

Paper: Liu, Sijie, Negin Nazarian, Jianlei Niu, Melissa A. Hart, and Richard de Dear. “From Thermal Sensation to Thermal Affect: A Multi-Dimensional Semantic Space to Assess Outdoor Thermal Comfort.” Building and Environment 182 (September 1, 2020): 107112. https://doi.org/10.1016/j.buildenv.2020.107112.