## 3 Results and Discussion
### Analysis of Questionnaire (TSV, CSV, and CLV) Results  
Figure 8 shows the results of the questionnaires of the average TSV, CSV, and CLV of subjects according to the cabin and vent discharge air temperature under solar radiation. The TSV was 2.89 at a cabin temperature of 35 \({}^{\circ}\)C without vent cooling, which shows that subjects felt very hot. The TSV was significantly reduced to 1.33 when the HVAC with a vent discharge temperature of 12.5 \({}^{\circ}\)C was operated at a cabin temperature of 35 \({}^{\circ}\)C. That means that the thermal sensation of the subjects decreased from very hot to warm. At the cabin and vent discharge air temperatures of 30 and 16.5 \({}^{\circ}\)C, the TSV was 0, and it was confirmed that the subjects were in a thermally neutral state. Next, the TSV value gradually decreased as the cabin and vent discharge air temperatures were changed to 22.5 \({}^{\circ}\)C, and the subjects at a cabin and vent discharge air temperature of 22.5 \({}^{\circ}\)C were in a cold state because the TSV was \(-\)2.11.  
In the results of the CSV questionnaire, the CSV at a cabin temperature of 35 \({}^{\circ}\)C without vent cooling operation was \(-\)2.33, which was the lowest. This value indicated that the subjects felt great discomfort because of the high cabin temperature. When the cooling was operated with a vent discharge temperature of 12.5 \({}^{\circ}\)C under a cabin temperature of 35 \({}^{\circ}\)C, the CSV increased rapidly to \(-\)0.44, and the comfort sensation of subjects was similar to the neutral state. The subjects felt suddenly comfortable compared with the previous condition because the discharge air from the vent with a low temperature of 12.5 \({}^{\circ}\)C could quickly provide a comfortable environment to the driver, even though it was a hot cabin environment (35 \({}^{\circ}\)C). Then, the CSV increased up to cabin and vent discharge air temperatures of 25 and 20.5 \({}^{\circ}\)C, respectively. The CSV at cabin and vent discharge air temperatures of 25 and 20.5 \({}^{\circ}\)C was 1.33, which was the highest value recorded; thus, the survey result found that subjects felt the most comfortable in this condition. Next, the CSV decreased to 0.67 at a cabin and vent discharge air temperature of 22.5 \({}^{\circ}\)C. A cabin and vent discharge air temperature of 22.5 \({}^{\circ}\)C is relatively cold because of the direct contact of the low temperature air to the body of the driver.  
According to the results of the CLV questionnaire of the subjects during cooling in the indoor environment of the car, the CLV was the lowest. It was \(-\)1.78 at a cabin temperature of 35 \({}^{\circ}\)C without the vent cooling operation. During vent cooling with a low discharge air temperature of 12.5 \({}^{\circ}\)C, the CLV rapidly increased to \(-\)0.33. This is because of the operation  
Figure 8: Variations of TSV, CSV, and CLV questionnaires.  
of vent cooling with a low temperature of 12.5 \({}^{\circ}\)C despite a hot cabin temperature of 35 \({}^{\circ}\)C. The vent cooling provided a thermally pleasant environment to the driver and greatly improved concentration during driving. As the cabin temperature decreased, the CLV tended to increase, and the CLV increased to 1.33 at cabin and vent discharge air temperatures of 25 and 20.5 \({}^{\circ}\)C, respectively. However, when the cabin and vent discharge air temperatures were 22.5 \({}^{\circ}\)C, the CLV decreased to 0.56, which means the subjects felt cold and unpleasant, and the concentration of the drivers decreased owing to long-term driving. The CLV showed a similar result to that of the CSV. In the overall results of the subjective questionnaires (TSV, CSV, and CLV), the subjects were comfortable and had a high level of concentration in the temperature ranges of the cabin and vent discharge air temperatures of 30 and 16.5 \({}^{\circ}\)C to those of 25 and 20.5 \({}^{\circ}\)C, respectively.