# Infrared Thermography to Evaluate Thermal Comfort under Controlled Ambient Conditions
## 1 Introduction
### Skin Temperature  
Skin temperature is a key parameter for thermal comfort evaluations. Nevertheless, measuring skin temperature can be a complicated task, and several authors have carried out research to assess and propose methods for accurate assessments. [PERSON] et al. [5] usedthe skin temperatures measured with thermocouples located in different positions on the body and the time differential as the base of a new model for the prediction of transient thermal sensations during sedentary and walking conditions. The results indicated a good correlation between the predicted thermal sensations and the experimental results, validating the proposed model. [PERSON] et al. [6] also used thermocouples bonded to the body in several locations to find the most suitable ones to assess human thermal comfort. In this study, the reliability, sensitivity, and number of measurement locations were used to interpretate the results. The authors concluded that the calculation of the mean skin temperature using 10 locations was the most appropriate approach. Years later, [PERSON] et al. [7] conducted a similar study to investigate whether the mean skin temperature could also be used to assess individual thermal sensations at high environmental temperatures. The results proved it possible to use it beyond the range of current air temperatures.  
Instead of thermocouples, [PERSON] and [PERSON] [8] assessed body temperatures using a sensor device that consisted of an exposed thermistor with rapid response rates, which measured the skin temperatures in contact with the skin surface by absorbing heat through conduction. As in other studies, the main purpose of this study was investigating the possibility of using body skin temperatures measured in multiple locations to assess thermal sensations.  
[PERSON] et al. [9; 10] assessed the possibility of using only a single body location to evaluate the overall thermal state and predict the thermal comfort of the occupants. The selected location was the area between the wrist and the fingers on the dorsal side of the hand, because in this zone the arteries that channel heat loss from the body's core to the periphery meet. The skin temperatures were recorded using a contact sensor device connected to a microcontroller board, which converted the captured signals to skin temperature levels.  
In the experimental campaign carried out by [PERSON] et al. [11], the skin temperatures in several locations were measured to investigate both the overall thermal comfort and the local discomfort under various asymmetric radiance conditions. In addition to the skin temperature in 25 points of the body, the tympanic temperature, measured with radiative thermometer, and oral temperature, using a disposable thermometer, were also considered in this study. The authors concluded that the local skin temperatures changed depending on the environmental and thermal conditions, even if the mean skin temperature remained almost the same, highlighting the importance of also using the skin temperature distribution to express thermal comfort in heterogeneous environments.  
From the studies previously discussed, it is possible to point out that the most used methods for the determination of skin temperature required contact (e.g., thermocouples and temperature sensors bonded to the skin, digital thermometers that take temperature readings in the mouth, tympanic thermometers measuring the temperature inside the ear canal through infrared ray technology, and wristband sensors that assess the temperature of the body by contact with the wrist), being mostly intrusive procedures. Therefore, the use of IRT as a non-intrusive method of thermal comfort assessment is an interesting possibility that is now starting to be studied by the scientific community.