## 1 Introduction
### Main Considerations of Thermal Comfort in Open Spaces  
Creating a comfortable thermal environment in urban open spaces requires a good understanding of human thermal comfort outdoors. [PERSON] [3] proved in his work that indoor comfort indicators are not valid for outdoor use. He even discussed the need for more detailed dynamic models than in the interior due to the spatial and temporal variability of the excitations (air movement, solar radiation, or radiant exchanges with neighbouring surfaces). Numerous studies have been developed for analysing comfort/discomfort in open spaces, outdoor spaces, or semi-outdoor spaces. From the point of view of urban thermal comfort, the study of how an external environment may or may not generate thermal comfort conditions necessarily requires understanding how the human body exchanges energy with its immediate environment [4]. The energy exchange depends on a series of factors and parameters, the former refers to the characteristics of the people, and the latter are related to the microclimate of the urban environment where these people are located. [PERSON] et al. [5] demonstrated the difficulty of evaluating comfort in open spaces and the invalidity of conventional methods tested indoors. These authors proposed an alternative method that has been validated with a sample of more than 500 people. On that line, authors such as [PERSON] et al. [6] evaluated the importance of the direct and indirect effects of environmental and climatic factors on the thermal comfort of people as the primary users of these spaces. The study that they carried out determined that air temperature, wind speed, thermal radiation, and relative humidity are the variables that have the most significant impact on outdoor thermal comfort. [PERSON] et al. [7] analysed the effects of the microclimate parameters on the thermal sensation in different seasons of the year. The air temperature was the factor with the most significant influence on thermal comfort, but air temperature's relative contribution to wind child gradually decreased, changing the season from spring to winter. However, for thermal radiation, the trend of the contribution to wind chill was reversed. Likewise, [PERSON] et al. [8] corroborated the four variables mentioned above and determined that the variable with the most significant impact is the outside temperature, followed by the incident thermal radiation. Furthermore, they concluded that incident thermal radiation has a more significant impact on outdoor thermal comfort than wind speed, which is a factor that does not occur indoors. [PERSON] et al. [9] analysed the influence of air velocity and temperature on comfort and added the length of stay. The time dependence was an actual result that should be taken into account in outdoor applications. [PERSON] et al. [10] studied the effects on thermal comfort in a semi-open transition space. They analysed and determined that, when walking, the disturbance due to wind speed significantly impacted the thermal sensation, since the transfer of heat by convection on the skin's surface was improved. However, they highlighted the importance of controlling the radiant heat exchange in transition spaces to achieve thermal comfort. In conclusion, treatment indoors and outdoors is different. Achieving an acceptable level of long-term comfort outdoors is more difficult in summer than in winter. In addition to shading and reducing the entry of outside air, it is necessary to create cool surfaces to reduce radiation heating. From the literature review, radiant heat is one of the most representative heat fluxes in the energy balance in the skin or clothes. This argument is one of the foundations of this work. Radiant solutions for interiors have been studied without breaking down the radiant and convective effects. The radiant effect is desired and sought after in the conditioning of outdoor spaces. The review about thermal comfort in open spaces showed the most relevant key performance indicators for climatic comfort in open spaces.