Field study of a thermal environment and adaptive model in Shanghai

Facial skin temperature and its relationship with overall thermal sensation during winter in Changsha, China

Facial skin temperature has been applied to evaluate thermal comfort in a few studies, but the related theoretical basis is not sufficient. We conducted a climate-controlled experiment in winter. The air temperatures were 12, 15, 18, 21, and 24°C, and the relative humidity was set to 60%. During exposure (140 min), the subjects were in a sedentary state, and their thermal sensation, comfort, and acceptability of perceived thermal environments were documented many times. iButton instruments were used to continuously and automatically record skin temperatures on the forehead, nose, right ear, right cheek, left cheek, left ear, and chin. The measurement accuracy of the corrected skin temperature was within 0.1°C after calibrating each i-Button. The experimental results showed that the skin temperatures at different measurement points varied significantly. The forehead skin temperature was the highest, whereas the nose, being the facial part, exhibited the lowest skin temperature (except 24°C). The uneven degree of the skin temperature distribution increased as air temperature decreased. Correlation analysis confirmed that the facial skin temperature can be used to evaluate thermal sensation. Nose skin temperature and the average skin temperature of the forehead, nose, and chin are the most suitable indicators of thermal sensation. The correlation between facial skin temperature and the thermal sensation was significantly higher after 15 min of exposure time than that during 0-15 min. This study provides a theoretical basis for using facial skin temperature to dynamically monitor thermal sensations.

Interpretability analysis for thermal sensation machine learning models: An exploration based on the SHAP approach

Machine learning models have been widely used for studying thermal sensations. However, the black-box properties of machine learning models lead to the lack of model transparency, and existing explanations for the thermal sensation models are generally flawed in terms of the perspectives of interpretable methods. In this study, we perform an interpretability analysis using the "SHapley Additive exPlanation" (SHAP) from game theory for thermal sensation machine learning models. The effects of different features on thermal sensations and typical decision routes in the models are investigated from both local and global perspectives, and the properties of correlation between features and thermal sensations and decision routes within machine learning models are summarized. The differences in the effects of features across samples reflect the effects of features on thermal sensations not only can be demonstrated by significant magnitudes but also by differentiation. The effects of features on thermal sensations often appear in the form of combinations of two to four features, which determine the final thermal sensation in most cases. Therefore, the neutral environment may actually be a dynamic high-dimensional space consisting of certain combinations of features in certain ranges with changing shapes.

Associations of bedroom air temperature and CO2 concentration with subjective perceptions and sleep quality during transition seasons

This field study aimed to investigate naturally ventilated bedroom environment and its effects on subjective perception and sleep quality. Totally, 104 healthy subjects living in urban areas of Beijing participated in the study for one night during transition seasons. Bedroom environment parameters, including temperature, relative humidity, and CO₂ concentration, were recorded before and during sleep. Objective sleep quality was measured by Fitbit Alta 2, a wrist-type actigraphy sensor. Subjective assessments were collected by paper-based questionnaires on sleep quality and environmental perceptions. The results showed that neutral temperature for waking state (before sleep) was estimated to be 23.8°C while for sleep state it was 26.5°C. Furthermore, pre-sleep thermal sensation vote was found to be positively correlated with deep sleep percentage. Indoor air quality was correlated with sleep quality as indicated by statistically significant correlations between odor intensity assessment, air quality acceptability, average nightly CO₂ concentration, and measures of sleep quality. For naturally ventilated bedrooms during transition seasons with a mild outdoor climate, present findings suggest that a bedroom with slightly warm pre-sleep environment than neutral, and with high ventilation as indicated by low indoor CO₂ concentration, could be beneficial for sleep quality of residents.

A Field Investigation on Adaptive Thermal Comfort in an Urban Environment Considering Individuals’ Psychological and Physiological Behaviors in a Cold-Winter of Wuhan

To date, studies of outdoor thermal comfort (OTC) have focused primarily on physical factors, tending to overlook the relevance of individual adaptation to microclimate parameters through psychological and physiological behaviors. These adaptations can significantly affect the use of urban and outdoor spaces. The study presented here investigated these issues, with a view to aiding sustainable urban development. Measurements of OTC were taken at a university campus and in urban spaces. Simultaneously, a large-scale survey of thermal adaptability was conducted. Two groups were selected for investigation in a cold-winter-and-hot-summer (CWHS) region; respondents came from humid subtropical (Cfa) and hot desert (BWh) climates, according to the Köppen Climate Classification (KCC). Results showed that: (1) neutral physiological equivalent temperature (NPET) and preferred PET for people from the Cfa (PCfa) and BWh (PBWh) groups could be obtained with KCC; (2) PCfa adaptability behaviors were, subjectively, more adjustable than PBWh; (3) Clothing affected neutral temperature (NT), where NT reduced by approximately 0.5 °C when clothing insulation rose 0.1 Clo; and (4) Gender barely affected thermal acceptance vote (TAV) or thermal comfort vote (TCV) and there was a substantial relationship between thermal sensation, NT, and PET. These findings suggest ‘feels like’ temperature and comfort may be adjusted via relationships between microclimate parameters.

Adaptive-rational thermal comfort model: Adaptive predicted mean vote with variable adaptive coefficient

Thermal adaptations, as feedbacks of occupants to physical stimuli, extend thermal comfort zone thereby reducing building energy consumption effectively. The rational approach models thermal comfort from the perspective of the body's heat balance, but is limited in explaining the thermal adaptations. The adaptive approach of modeling thermal comfort can fully account for the thermal adaptations, but ignores the body's heat balance. To improve thermal comfort prediction, this study proposes an adaptive-rational thermal comfort model, that is, an adaptive predicted mean vote with a variable adaptive coefficient (termed as arPMV). By linearly linking the negative feedback effects of the thermal adaptations to the ambient temperature according to the adaptive approach, the variable adaptive coefficient is linearly related to the reciprocal of the ambient temperature with two constants. The variable adaptive coefficient is determined by explicitly quantifying the two constants as the functions of the predicted mean vote, thermal sensation vote, and ambient temperature. The proposed arPMV is validated for naturally ventilated, air-conditioned, and mixed-mode buildings, with the mean absolute error and the robustness of the thermal sensation prediction reduced by 24.8%-83.5% and improved by 49.7%-83.4%, respectively.

Investigations on the Winter Thermal Environment of Bedrooms in Zhongxiang: A Case Study in Rural Areas in Hot Summer and Cold Winter Region of China

In this paper, onsite measurements and a subjective questionnaire were conducted to study the thermal environment and heating condition of bedrooms during the winter in rural areas in China’s hot summer and cold winter (HSCW) region. Indoor and outdoor thermal environmental parameters were measured to evaluate the thermal conditions of bedrooms. Thermal sensation/tendency/acceptance, heating, and health condition were investigated to complete the analysis of attitudes of local residents on the thermal environment of bedrooms, heating and health issues, as well as the analysis of buildings. The observed results demonstrate that occupants in this region have a strong tolerance to low-temperature environments with the 80% acceptable lower temperature of 4.7 °C and a neutral temperature of 10.7 °C, with an average clothing insulation over 2.2 clo. Oversized volume and acreage of buildings and windows induce a lower temperature in the bedroom. Infants have a significant effect on heating requirements, including heating duration and temperature setpoint. Local residents are highly concerned about the costs, safety, and health related to heating and thermal environments. All evidence obtained through this investigation shows that it is beneficial to formulate regulations for the shape, envelope, and centralized heating policy for rural residential buildings in the HSCW region.

Investigation of indoor environmental quality in Shanghai metro stations, China

A field study was carried out in Shanghai metro stations to gather and evaluate information about the real environment. The thermal environment and particulate matter levels were monitored in this study. The mean thermal sensation vote in metro stations was 0.91, and the mean thermal neutral temperature was 20.6 degrees C. Although 92.1% of subjects voted that the thermal environment was acceptable, the condition of air quality in Shanghai metro stations was not good. The mean levels of PM1.0, PM2.5, and PM10 were 0.231+/-0.152, 0.287+/-0.177, and 0.366+/-0.193 mg/m3, respectively. The contribution of PM1.0 to PM2.5 and PM2.5 to PM10 was up to 79% and 76%, respectively. This means that fine particles or ultrafine particles constituted the preponderant part of metro station particulate matter.

Thermal comfort in naturally ventilated and air-conditioned buildings in humid subtropical climate zone in China

A thermal comfort field study has been carried out in five cities in the humid subtropical climate zone in China. The survey was performed in naturally ventilated and air-conditioned buildings during the summer season in 2006. There were 229 occupants from 111 buildings who participated in this study and 229 questionnaire responses were collected. Thermal acceptability assessment reveals that the indoor environment in naturally ventilated buildings could not meet the 80% acceptability criteria prescribed by ASHRAE Standard 55, and people tended to feel more comfortable in air-conditioned buildings with the air-conditioned occupants voting with higher acceptability (89%) than the naturally ventilated occupants (58%). The neutral temperatures in naturally ventilated and air-conditioned buildings were 28.3 degrees C and 27.7 degrees C, respectively. The range of accepted temperature in naturally ventilated buildings (25.0-31.6 degrees C) was wider than that in air-conditioned buildings (25.1-30.3 degrees C), which suggests that occupants in naturally ventilated buildings seemed to be more tolerant of higher temperatures. Preferred temperatures were 27.9 degrees C and 27.3 degrees C in naturally ventilated and air-conditioned buildings, respectively, both of which were 0.4 degrees C cooler than neutral temperatures. This result suggests that people of hot climates may use words like "slightly cool" to describe their preferred thermal state. The relationship between draught sensation and indoor air velocity at different temperature ranges indicates that indoor air velocity had a significant influence over the occupants' comfort sensation, and air velocities required by occupants increased with the increasing of operative temperatures. Thus, an effective way of natural ventilation which can create the preferred higher air movement is called for. Finally, the indoor set-point temperature of 26 degrees C or even higher in air-conditioned buildings was confirmed as making people comfortable, which supports the regulation in China that in public and office buildings the set-point temperature of air-conditioning system should not be lower than 26 degrees C.