# Infrared Thermography to Evaluate Thermal Comfort under Controlled Ambient Conditions
## 1 Introduction
### Assessing Thermal Comfort via IRT  
The impact of skin temperature on the thermal sensation has been studied by several authors, and some also proposed methodologies to correlate the two. [PERSON] et al. [12] explored the suitability of using ambient air sensors, wrist skin temperature using wearable sensors, and IRT to measure different regions of the face (i.e., forehead, nose, left and right cheekbones) to predict individual thermal sensations. The experiment was conducted in a controlled and uniform environment with changes in air temperature from 19 \({}^{\circ}\)C to 29 \({}^{\circ}\)C. During the measurements, the feedback of the participants regarding the thermal sensations was collected. The results indicated that the models using ambient temperature data presented higher accuracy (about 81%) in predicting thermal comfort when compared to using the measurements from the wrist sensor (about 76%) or the temperatures of the face quantified via IRT (about 75%). However, when combining the ambient temperature data with the data obtained with the sensor or with IRT, the prediction accuracy increased to about 83%, and when all data were combined the accuracy increased to about 85%. According to [PERSON] et al. [13], the skin temperatures are similar when measured through a PT100 platinum resistance thermometer and an infrared camera. In order to compare the accuracy of both methods, a single tracking point was selected (the center of the forehead). Furthermore, the disadvantages of the contact measurements were detected, such as the effects of physical pressure, the insulation effect due to the fitting material, and the thermal inertia of the sensor. The body region used to assess the skin temperature is also an open issue. This aspect includes the necessary compatibility between the feasibility of the measurement and its accuracy. The face temperature has been selected by most of the researchers for studies using IRT in the assessment of thermal comfort. According to [PERSON] et al. [14], this region is of interest because there is a high density of blood vessels on the areas around the face, and additionally this body area is not usually covered by clothing when inside buildings. According to the literature review, the evaluations of facial temperatures using IRT are usually focused on specific regions, such as the nose, the cheekbones, and the forehead [12; 15]. Other regions of interest were considered by [PERSON] et al. [14; 16], who assessed the temperatures of the ears. [PERSON] et al. and [PERSON] et al. [13; 17] measured the temperature of the chin. [PERSON] et al. [13] evaluated the temperatures of the mouth, the eye, and the inner eye corner, and [PERSON] et al. [18] studied the face as a whole. These works have shown that different areas of the face behave differently during the heating phase, the cooling phase, and in steady-state conditions. [PERSON] et al. [13] detected the highest temperature in the inner eye corner, followed by the center of the forehead, which presented a more homogeneous temperature distribution. The authors also found more variability in the cheekbones. Another application of IRT in the study of thermal comfort is the measurement of clothing temperatures. [PERSON] et al. [13] explored the influence of clothing layers using the chest region for the measurements. Four different combinations were assessed: (i) no clothes; (ii) shirt; (iii) sweater; (iv) winter jacket. The skin temperature (no clothes) corresponded to the highest value of the four combinations, with the temperature decreasing from (i) to (iv), i.e., higher insulation resulted in lower measured layering temperatures. [PERSON] et al. [17] studied the thermal neutrality of the clothing temperature as well as the skin temperature (resulting from the average of four facial points, i.e., the nose, cheekbones, forehead, and chin), reaching values of 31 \({}^{\circ}\)C and 35 \({}^{\circ}\)C, respectively. [PERSON] et al.