# Metabolic Rate Measuring with Indirect Calorimetry for Thermal Comfort Evaluation
## 3 Results and Discussion
### Predictive Equations for MET Based on Walking Speed  
As the observation method in ISO 8996-2004 mentioned, predictive equations can estimate the MET values of daily activities. In this study, all MET values at each activity intensity were considered as a whole since the varying environments have little impact on MET (except for the 6 km/h walking activity in the hot environment). The linear and nonlinear relationships between walking speed (km/h) and MET (W/m\({}^{2}\)) for 30 subjects (120 person-time) were fitted. In addition, some linear equations were fitted through the mean values of MET at each activity from other related research [7; 8; 15; 20]. Figure 9a gives the linear relationships between walking speed and MET in this study, and Figure 9b shows the comparisons of this study and others. The specific details of the linear relationships are listed in Table 4.  
Figure 7: Variation of MET in various environments. The R\({}^{2}\) of all equations is larger than 0.9, indicating that the linear correlation is a good representation of the relationship between MET and walking speed. However, there are disparities in the slopes and intercepts of them. The slope and intercept in the ASHRAE Handbook are the lowest in these studies, indicating that the MET values are evidently underestimated. The deviation is caused by the limitations of measuring equipment and most data come from investigations in the 20 th century [24]. The slopes of [PERSON]'s and [PERSON]'s studies are comparable and significantly higher than those of this study and \begin{table}
\begin{tabular}{c c c c} \hline
**Research** & **Linear Relationships** & **R\({}^{2}\)** & **Data Sources** \\ \hline This study & MET = 28.38 \(\times\) Speed + 62.25 & 0.99 & China \\ [PERSON]’s study & MET = 33.30 \(\times\) Speed + 52.40 & 0.97 & India \\ [PERSON]’s study & MET = 34.44 \(\times\) Speed + 54.33 & 0.95 & China \\ ISO 8996 & MET = 28.65 \(\times\) Speed + 53.78 & 0.99 & Europe \\ ASHRAE Handbook & MET = 24.65 \(\times\) Speed + 50.60 & 0.94 & America \\ \hline \end{tabular}
\end{table} 
Table 4: The specific details of the linear relationships. Figure 8: Variation of HR in various environments. Figure 9: (**a**) The linear relationships between walking speed and MET, (**b**) the comparisons of this study and other studies. ISO 8996. The reasons are that there is a lack of MET at high-activity intensities in [PERSON]'s study, and the MET at high-activity intensities in [PERSON]'s study is higher. For [PERSON]'s study, the mean value of MET at 6 km/h walking is 284.4 W/m\({}^{2}\), which is higher than that in this study (253.9 W/m\({}^{2}\)). This difference may be due to the influence of barometric pressure on the MET [25; 26]. [PERSON] et al. measured the MET of 5.4 km/h walking activity in various barometric pressures. The results showed that the MET in 0.95 atm is higher by 5.4% than that in 1 atm condition [25]. [PERSON]'s research is conducted in Xi'an, China, where the altitude is about 450 m, but this study is conducted in Tianjin, China, where the altitude is about 4 m. This results in a disparity in atmospheric pressure of about 0.05 atm between the two places. Therefore, the MET of 6 km/h walking activity in [PERSON]'s study is higher than in this study. It is worth noting that the intercept of this study is higher than others. It indicates that the MET of sitting activity in this study is higher than others. The reason is that the subjects of this study are younger than other studies, and they are more energetic. In summary, there are some discrepancies in these predictive equations for MET based on walking speed. When using these equations, it is necessary to take barometric conditions into account, especially at high activity intensities. In addition, the age difference causes the subjects to have a higher MET while conducting the sitting activity. The prediction equations in this study can provide a more accurate prediction of MET for people in schools, gyms, and other places in the plains.