Identification and assessment of the effect of environmental, personal and social components on thermal comfort in office buildings

Thermal comfort is one of the comfort aspects in current architectural design and can be changed by various components. Researchers emphasize that early thermal comfort studies relying on climate and environmental aspects can only justify a  part of the results. Therefore, it is necessary to examine the effect of other components. Effective components could be found in physical, physiological, psychological, social, environmental, and economic aspects. So, thermal comfort can be influenced by inner and outer factors. Regarding the research literature and the variety of effective components in thermal comfort, there is a lack of research on this subject. In addition, researchers believe many relations between these components should be considered in thermal comfort studies. Therefore, as a part of a larger study, this study was conducted to investigate the effect of personal, environmental, and social components on thermal comfort. This study aims to clarify the individual and social components affecting the perception of thermal comfort to provide solutions to improve the design of office spaces. So, there are two questions: First, what are the personal and social factors affecting the perception of thermal comfort? And second, which scale is better for predicting thermal comfort based on these components?

In this regard, a field study (including questionnaire, observation, and on-site measurement for recording climatic data using thermal sensors) was conducted in winter in a main administrative office building of Shiraz University. Questionnaires were designed to gather some of the personal components (such as age, gender, height, weight, and adaptive behaviors); social components (including education and degree level, the field of study, and position); and thermal scales (thermal sensation, thermal comfort, thermal satisfaction, thermal preference, thermal acceptability, and overall thermal comfort). Blood pressure, heart rate, and body temperature as the personal components were measured using a related standard device. Clothing and activity types were recorded and then changed into a quantitative scale. The data loggers also record the indoor air temperature and relative humidity. The field study was conducted in January 2019 for four consecutive days from 8 am to 12 pm. In total, there were 110 measurement subjects. Finally, 108 were identified as useful in the analysis by eliminating incomplete questionnaires. The main administrative building is located on the northern side of Shiraz, Iran (52.52°N, 29.63°E). The 138920 m2 building is oriented in the northwest and southeast in two blocks (with seven and ten stores). The two building blocks have some differences in constructional details and interior design. There was no compulsion to participate, and oral and short-form written consent was considered with no restrictions on participants to have freedom of their usual work day.

The collected data were imported into SPSS software. A total of 22 statistical analyses were performed, including descriptive and inferential statistics (linear and multiple linear regression, Univariate ANOVA). This study selected the correlation coefficients based on the variables scale. So, Spearman, Pearson, and Eta correlation have been used to show the strength of the relations. In this study, 108 subjects participated, including 41 women and 66 men (one person did not mention gender). The age group varies from 24 to 60 years. Most of the age group is in the 31-45 range. These individuals weigh between 50 and 120 kg and have a height of 1.55 to 1.86 meters. The average body temperature was 36°C, the mean blood pressure was 126 with a minimum of 87 and a maximum of 183, and the heart rate was also in the range of 49 to 98. The average indoor air temperature during the four days of study was 23.67°C, and the average relative humidity was 24.86%. The indoor globe temperature was very close to the air temperature (23.50°C). The average outdoor temperature was 15.2°C, and the average relative humidity was 34.9%. The thermal response was considered with nine different thermal scales on the 3,5, and 7-point Likert scale. The average of each response was as follows: Thermal sensation vote (TSV)= -0.4; Thermal comfort=6; Thermal pleasure= 4.78; Temperature preferences= 0.3’ Humidity preferences= -0.18; Velocity preferences= -0.35; Radiation preferences=-0.32; Thermal acceptance= 0.85; & overall thermal comfort= 4.94.

The results show that the impact of social components is negligible. However, participants in double and multiple office rooms had better thermal comfort status than in single office rooms. So, if these criteria are considered during the design process, it can help to improve the indoor environmental quality. Regarding the personal components, body mass index and clothing value are the two most influential factors. It is very important to make different thermal adaptation strategies for the occupants to have a right to choose any of them. Therefore, appropriate strategies should be considered for the components needed to provide comfortable conditions in both human resource management and architectural design. In this study, the thermal preference is an appropriate scale for predicting occupants’ thermal needs based on environmental and personal components. The thermal comfort range was calculated based on Griffith’s methods and was 21-26°C. It is very important to know that people feel neutral based on the thermal sensation vote in most office buildings. Still, they usually need temperature, humidity, air velocity, and radiation changes. So in architecture or mechanical engineering, we should not merely rely on thermal sensation vote to decide on heating or cooling setpoints. So, if the setpoint of the studied office building changes from 25°C to 23.6°C, we can anticipate at least a 10 percent reduction in energy consumption. People can adapt to different situations, making them flexible and resilient. But designers should be aware that this adaptation process needs more effort and, of course, more mental, psychological, and physical energy that can reduce occupant’s productivity.