# Experimental Investigation into the Thermal Performance of Personal Cooling Mechanisms
## 2 Materials and Methods
### Experimental Procedure
#### 2.3.2 Testing Protocol  
The testing method used for this evaluation was based on a new testing protocol developed to evaluate cooling systems [45]. This test method was successfully compared with the data generated following the ASTM F2371 standard for low, moderate and high metabolic rates of activity. The parameters evaluated in this study to assess the performance of the different cooling mechanisms were:  
* Local skin temperature (T\({}_{\text{sk}}\)): Taken directly from each region of the manikin and calculated from the model. In this case, it was the mean skin temperature of the torso region. * Hypothalamus temperature (T\({}_{\text{hy}}\)): The hypothalamus temperature is the most representative of cardiac and brain temperature and represents the core temperature measurement in this software. The hypothalamus is the centre of our body's thermoregulation and controls our internal temperature, activating, for example, evaporation in case of an increase in our core temperature, so it is an essential parameter to evaluate the thermal comfort of the body. * Thermal comfort index: According to a 7-point scale from \(-3\) (very uncomfortable) to 3 (very comfortable) from the ISO 10551-19 standard. * Thermal sensation index: According to the ASHRAE-55-2023 standard with a 7-point scale ranging from \(-3\) (cold) to 3 (hot). The environmental conditions used were the same as those used for the ASTM F2371-24 and ASTM F2300-22 standards. The climatic chamber was set to an air temperature of 35.0 \(\pm\) 0.5 \({}^{\circ}\)C, a relative humidity of 40 \(\pm\) 5%, and an air velocity of 0.4 \(\pm\) 0.1 m/s. The manikin was placed in the centre of the climate chamber, wearing the sweating system. At the start of each test, we needed the manikin to be in a thermoneutral state, with a mean skin temperature of 34.4 \({}^{\circ}\)C throughout the body and a hypothalamus temperature \begin{table}
\begin{tabular}{c c c} \hline
**Cooling Vest** & **Cooling Mechanism** & **Accessories** \\ \hline
1 & Cooling water circulation & Pump, cooling system, battery \\
2 & Air circulation & Battery \\
3 & Water evaporation & — \\
4 & PCMs (28 \({}^{\circ}\)C) & PCM packs \\ \hline \end{tabular}
\end{table} 
Table 3: Cooling vests were used in this study. Figure 2: The trunk of the manikin. of 37.0 \({}^{\circ}\)C. The manikin achieved this thermoneutral state using the software option \"thermoneutral state\". This preliminary test ensures that the manikin is in the same neutral state before each test. Upon completing this baseline assessment, the manikin was outfitted with different cooling vests and subjected to the identical testing protocol. Some vests need preliminary preparation before dressing the manikin with the samples for testing to ensure that the cooling mechanisms are working:  
1. Cooling vests 1: charge the battery and fill the reservoir with water. 2. Cooling vests 2: charge the battery. 3. Cooling vests 3: immerse in water and drain. 4. Cooling vests 4: Place the PCM packs in a freezer at \(-50.0\)\({}^{\circ}\)C for 40 min. The data obtained from the software are affected by several factors, including environmental conditions, the sample being analysed, the simulated activity, and its duration. Therefore, the only parameter we needed to input into the software to evaluate the thermal performance of the samples was the metabolic rate of the activity we wanted to simulate. Table 4 shows activity levels and their metabolic rates according to ISO 8996-2021 [46], with the equivalence of the metabolic rate in different units. The metabolic rate in the software is displayed in Metabolic Equivalent of Task Units (met), where 1 met corresponds to 58.2 W/m\({}^{2}\). In this evaluation, the performance of the cooling vests was assessed across three different activity levels: low metabolic rate (1.4 met), moderate metabolic rate (2.8 met), and high metabolic rate (4.0 met). Each activity was simulated for 20 min, starting with the lowest metabolic rate and finishing with the highest.