Comparative analysis on indoor and outdoor thermal comfort in transitional seasons and summer based on multiple databases: Lessons learnt from the outdoors.

In environments with similar physical parameters, thermal comfort and sensation feelings may differ indoors and outdoors. How indoor and outdoor thermal perception differ from each other remains unclear. This study compared and discussed 29,536 field survey data, including 19,191 sets of indoor data, and 10,345 sets of outdoor data, covering five Köppen climate zones during transitional seasons and summer. Indoor data points were collected from two databases: the ASHRAE Global Thermal Comfort II and the SCATs (Smart Controls and Thermal Comfort), while outdoor data points were collected from the RUROS database (Rediscovering the Urban Realm and Open Spaces) and five individual projects executed in Singapore, Hong Kong, Guangzhou, Changsha, and Tianjin. The concepts of neutral rate (NR) and comfort rate (CR) were developed to help categorize "neutral" and "comfort" across different studies. The results of this study show that people are less sensitive to changes in thermal environment outdoors than indoors. Moreover, thermal comfort cannot be simply treated as thermal neutral, particularly for outdoor spaces. Compared with MM (mixed-mode) and NV (naturally ventilated) spaces, outdoor space does not have the highest NR, but its CR is much higher, with a wide range of SET* (Standard Effective Temperature) corresponding to CR over 80 %, from 15.5 °C to 23.4 °C. In the Cfa (humid subtropical) climate zone, significantly higher CR are recorded for outdoor spaces, although the NR are similar or even lower than those of indoors. Natural thermal resources in the outdoor thermal environment may hold the key to extending indoor comfort ranges.

Comparing the effects of sun and wind on outdoor thermal comfort: A case study based on longitudinal subject tests in cold climate region.

Sun and wind are important physical factors that influence outdoor thermal comfort. This study compared the impact of sun and wind on outdoor thermal sensation by analyzing 3546 samples of subject test data during a case study in a cold climate city Tianjin, China. The data was collected from subject tests conducted under air temperatures ranging from 3.8 °C to 35.2 °C (mean 20.2 °C), wind from 0 to 4.8 m/s (mean 0.6 m/s), mean radiant temperature 1.8 to 68.9 °C (mean 36.8 °C) in Tianjin, China. In this particular study, the sun was found to be a more significant factor than wind during the test. Standardized linear regression of the pooled dataset revealed that the contributions of air temperature, sun, wind, and humidity to thermal sensation were 56%, 29.4%, 8.8%, and 5.9%, respectively. When compared under different air temperature ranges, the effect of sun was more than two times greater that of wind. When the air temperature was in the range of 5-10 °C, solar exposure increased the thermal sensation by more than 2 units, but a reduction in wind speed had no observable effect on thermal sensation. When the air temperature was as high as 30-35 °C, increasing the wind by up to 2 m/s lowered the thermal sensation in the shade, but not in the sun. A summary of pedestrian level wind measured in real urban spaces in 28 previous studies indicated that urban spaces generally have low wind speeds, with the median value of mean wind speed of 0.8 m/s. The results of this study provide useful information for designs to creating comfortable urban open spaces.

Evaluation of SARS-COV-2 transmission and infection in airliner cabins.

Commercial airliners have played an important role in spreading the SARS-CoV-2 virus worldwide. This study used computational fluid dynamics (CFD) to simulate the transmission of SARS-CoV-2 on a flight from London to Hanoi and another from Singapore to Hangzhou. The dispersion of droplets of different sizes generated by coughing, talking, and breathing activities in a cabin by an infected person was simulated by means of the Lagrangian method. The SARS-CoV-2 virus contained in expiratory droplets traveled with the cabin air distribution and was inhaled by other passengers. Infection was determined by counting the number of viral copies inhaled by each passenger. According to the results, our method correctly predicted 84% of the infected/uninfected cases on the first flight. The results also show that wearing masks and reducing conversation frequency between passengers could help to reduce the risk of exposure on the second flight.

Estimating long-term time-resolved indoor PM2.5 of outdoor and indoor origin using easily obtainable inputs.

To evaluate the separate impacts on human health and establish effective control strategies, it is crucial to estimate the contribution of outdoor infiltration and indoor emission to indoor PM2.5 in buildings. This study used an algorithm to automatically estimate the long-term time-resolved indoor PM2.5 of outdoor and indoor origin in real apartments with natural ventilation. The inputs for the algorithm were only the time-resolved indoor/outdoor PM2.5 concentrations and occupants' window actions, which were easily obtained from the low-cost sensors. This study first applied the algorithm in an apartment in Tianjin, China. The indoor/outdoor contribution to the gross indoor exposure and time-resolved infiltration factor were automatically estimated using the algorithm. The influence of outdoor PM2.5 data source and algorithm parameters on the estimated results was analyzed. The algorithm was then applied in four other apartments located in Chongqing, Shenyang, Xi'an, and Urumqi to further demonstrate its feasibility. The results provided indirect evidence, such as the plausible explanations for seasonal and spatial variation, to partially support the success of the algorithm used in real apartments. Through the analysis, this study also identified several further development directions to facilitate the practical applications of the algorithm, such as robust long-term outdoor PM2.5  monitoring using low-cost light-scattering sensors.

Associations of indoor carbon dioxide concentrations, air temperature, and humidity with perceived air quality and sick building syndrome symptoms in Chinese homes.

The indoor environment influences occupants' health. From March 1, 2018, to February 28, 2019, we continuously monitored indoor temperature (T), relative humidity (RH), and CO2 concentration in bedrooms via an online system in 165 residences that covered all five climate zones of China. Meanwhile, we asked one specific occupant in each home to complete questionnaires about perceived air quality and sick building syndrome (SBS) symptoms at the end of each month. Higher CO2 concentration was significantly associated with a higher percentage of perceived stuffy odor and skin SBS symptoms. Higher relative humidity was associated with higher percentage of perceived moldy odor and humid air, while lower RH was associated with a higher percentage of perceived dry air. Occupants who lived in residences with high RH were less likely to have mucosal and skin SBS symptoms (adjusted odds ratio (AOR): 0.73-0.78). However, the benefit of high humidity for perceived dry air and skin dryness symptoms is weaker if there is a high CO2 concentration level.

A field investigation of the thermal environment and adaptive thermal behavior in bedrooms in different climate regions in China.

Sleep thermal environments substantially impact sleep quality. To study the sleep thermal environment and thermal comfort in China, this study carried out on-site monitoring of thermal environmental parameters in peoples' homes, including 166 households in five climate zones, for one year. A questionnaire survey on sleep thermal comfort and adaptive behavior was also conducted. The results showed that the indoor temperature for sleep in northern China was more than 4°C higher than that in southern China in winter, while the indoor temperatures for sleep were similar in summer. Furthermore, 70% of people were satisfied with their sleep thermal environment. Due to the use of air conditioning and window opening in various areas in summer, people were satisfied with their sleep thermal environments. Due to the lack of central heating in the southern region in winter, people feel cold and their sleep thermal environment needs further improvement. The bedding insulation in summer and winter in northern China was 1.83clo and 2.67clo, respectively, and in southern China was 2.21clo and 3.17clo, respectively. Both northern China and southern China used air conditioning only in summer. People in southern China opened their windows all year, while those in northern China opened their windows during the summer and transitional periods.

A comprehensive review of thermal comfort studies in urban open spaces.

Urban open spaces provide various benefits to large populations in cities. Since thermally comfortable urban open spaces improve the quality of urban living, an increasing number of studies have been conducted to extend the existing knowledge of outdoor thermal comfort. This paper comprehensively reviews current outdoor thermal comfort studies, including benchmarks, data collection methods, and models of outdoor thermal comfort. Because outdoor thermal comfort is a complex issue influenced by various factors, a conceptual framework is proposed which includes physical, physiological and psychological factors as direct influences; and behavioral, personal, social, cultural factors, as well as thermal history, site, and alliesthesia, as indirect influences. These direct and indirect factors are further decomposed and reviewed, and the interactions among various factors are discussed. This review provides researchers with a systematic and comprehensive understanding of outdoor thermal comfort, and can also guide designers and planners in creating thermally comfortable urban open spaces.

A review of mitigating strategies to improve the thermal environment and thermal comfort in urban outdoor spaces.

Urban open space provides various benefits to citizens, but the thermal environment of this space is impacted by global warming and urban heat islands. A growing number of studies have been conducted on strategies for improving the urban thermal environment and attracting more people to outdoor spaces. This paper reviews the mechanisms and cooling effects of four major mitigation strategies, namely, changing the urban geometry, planting vegetation, using cool surface, and incorporating bodies of water. Our review found that on summer days these four strategies yielded a median reduction in air temperature of 2.1 K, 2.0 K, 1.9 K, and 1.8 K, respectively. In terms of integrated effect on thermal comfort, changing the urban geometry provided the greatest improvement, with the largest reduction in physiologically equivalent temperature (PET) in summer (median ΔPET = 18.0 K). The use of vegetation and water bodies reduced the median PET by 13.0 K and 4.6 K, respectively. However, some simulation studies found that reflective surface led to higher PET in summer because of the increased amount of reflected solar radiation. The mitigation strategies improved the urban thermal environment to a greater extent in hotter and drier climates. Vegetation, cool surface, and water bodies provided less cooling in compact urban spaces than in open areas. The results that we reviewed can be used by designers and planners seeking to create thermally comfortable urban open spaces.

A simple method for differentiating direct and indirect exposure to exhaled contaminants in mechanically ventilated rooms.

Many airborne infectious diseases can be transmitted via exhaled contaminants transported in the air. Direct exposure occurs when the exhaled jet from the infected person directly enters the breathing zone of the target person. Indirect exposure occurs when the contaminants disperse in the room and are inhaled by the target person. This paper presents a simple method for differentiating the direct and indirect exposure to exhaled contaminants in mechanically ventilated rooms. Experimental data for 191 cases were collected from the literature. After analyzing the data, a simple method was developed to differentiate direct and indirect exposure in mixing and displacement ventilated rooms. The proposed method correctly differentiated direct and indirect exposure for 120 out of the 133 mixing ventilation cases and 47 out of the 58 displacement ventilation cases. Therefore, the proposed method is suitable for use at the early design stage to quickly assess whether there will be direct exposure to exhaled contaminants in a mechanically ventilated room.