# Metabolic Rate Measuring with Indirect Calorimetry for Thermal Comfort Evaluation
## 1 Introduction  
Thermal comfort is perceived as an essential factor for the well-being and productivity of the occupants. Thermal comfort is defined as that \"condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation\" by ASHRAE Standard 55 [1]. In the field of thermal comfort research, the results of Prof. [PERSON] [2] are most representative. To date, the predicted mean vote (PMV), which is proposed by him, is the broadest index of thermal comfort evaluation from all over the world. At present, lots of standards in Europe, the United States, China, and India are also written on this basis [3, 4, 5, 6]. There are six fundamental parameters of the PMV index, which are air temperature, air humidity, mean radiant temperature, air velocity, clothing insulation, and metabolic rate (MET) [2]. The environmental parameters can often be measured with relatively simple and inexpensive equipment [3]. Moreover, the values of clothing insulation are always summed in individual garment insulation according to the standards in [1, 3]. For example, if an adult man wears a short-sleeved garment with a clothing insulation of 0.05 clo Clo and a long-sleeved garment with a clothing insulation of 0.07 clo, the total garment clothing insulation is 0.12 Clo. On the contrary, the measurement of MET is complex. The simple and direct method is to read the 'activity diary' from the standards in [7, 8], which is used in most thermal comfort studies [9, 10]. [PERSON] et al. used a vision-based approach to estimateMET to predict thermal sensation [9], whose MET data originates in ISO 8996-2004 [7]. For example, the MET is 55 W/m\({}^{2}\) at sitting activity, and the MET is 110 W/m\({}^{2}\) at 2 km/h walking activity without load. [PERSON] et al. analyzed the relationship between thermal sensation and thermal comfort of people with different activity intensities in the urban park during winter in cold regions of China [10]. They graded the different activities based on the MET data in ASHRAE Standard 55 [1]. Despite the simplicity of this method, its accuracy is low, and there are often some mistakes. According to several recent studies, there are underestimation errors in the 'activity diary' of the ASHRAE Handbook [8]. The other method with slightly higher precision is to estimate MET by measuring the heart rate [11; 12]. [PERSON] et al. conducted a thermal responses experimental study, and the MET of the subjects was calculated by the HR [11]. [PERSON] et al. investigated the possibility of using heart rate as a human factor for thermal sensation models [12]. Both of these methods cost little but may be less accurate. As science and technology evolve, indirect calorimetry becomes a great way to measure MET [13]. It works by measuring the amount of oxygen consumption (V\({}_{\text{O2}}\)) and carbon dioxide output (V\({}_{\text{CO2}}\)) of the body over a period to calculate MET. This method is regarded as the gold standard of human metabolism measurement due to its significant accuracy, although it requires expensive and complex equipment [7; 13]. Recently, this method has been adopted for thermal comfort studies [14; 15; 16; 17; 18; 19; 20]. [PERSON] et al. measured the MET of college-age Japanese subjects during various office activities [14]. The findings showed that the standards overestimated the MET and resulted in a variance of thermally neutral temperature. [PERSON] et al. obtained the MET of Indian subjects during sitting and walking activities and compared the PMV based on standards and observed MET [15]. However, many previous studies measured the MET only at a particular intensity of activity and resulted in somewhat restrictive applications. Therefore, it is necessary to develop some predictive equations for MET and investigate their application in thermal comfort. The purpose of this research is to obtain the MET at various activities using indirect calorimetry, to develop the predictive equations for MET, and to investigate their application in thermal comfort.