BPH3: Observation/surveys of outdoor comfort
Thermal comfort conditions of urban spaces in a hot-humid climate of Chiangmai city, Thailand
1Faculty of Architecture and Planning, Thammasat University, Thailand; 2Social Research Institute (SRI), Chiangmai University, Thailand
Urban spaces are most important to promote liveable cities because they accommodate pedestrians and various outdoor activities which contributing to urban livability and vitality. Thus, the urban microclimate is an important issue to determining the quality of urban spaces, especially in rapidly growing Asian cities in tropical climates. The aim of this study was to investigate thermal sensation for occupants of outdoor and semi-outdoor urban environments in wide range of hot-humid tropical climate conditions. The measurement period was conducted during the daytime from 8 am to 4 pm on April within the year 2014, which is the most representative a hottest month of summer in Chiangmai city. Thermal environment conditions of two different types of urban spaces were evaluated based upon the measurement of major climatic parameters, while the thermal acceptability of subjects was captured concurrently using a questionnaire survey. The respondents were conducted in a wide range of air temperature (34.8±3.2°C), relative humidity (40.7±7.3%), wind velocity (0.7±0.3m/s) and mean radiant temperature (40.3±8.8°C) for the climatic conditions in summer. The Thermal Sensation Vote (TSV) of the respondents were expressed on a 7-point scale ranging from -3 (very cold) to +3 (very hot), whereas the respondents were asked to rate their overall thermal comfort level (or acceptability) to determine the responses of individuals regarding the outdoor climatic conditions, along with personal parameters (e.g., age, gender, weight and height) and characteristics (e.g., clothing, activity etc.) of respondents.
A total of 296 questionnaires were collected in the outdoor (72.3%) and semi-outdoor (27.7%) urban spaces during the survey, which was carried out on days with suitable weather and avoid rainy days. Metabolic rate and clothing insulation were estimated in accordance with ASHRAE 55-2004. As only respondents who were sitting (1.2 met) and standing (1.4 met) were included during the survey. The average clothing values was found to be 0.55±0.20clo. In the meantime, the evaluation of PET (Physiologically Equivalent Temperature) index using the RayMan model was utilized to calculate the thermal comfort conditions in this study. The majority of the respondents (99.8%) stayed under trees or buildings shaded conditions. The 56.8% of the respondents were males. The average weight and height was 57.7±10.5 kg and 162.6±6.76 cm.
According to survey results, 28.97% and 26.83% of the respondents voted for neutral (TSV=0) in outdoor and semi-outdoor urban spaces respectively. The thermal neutrality was derived by solving the simple linear equations for a mean sensation vote of zero, which are determined by analyzing the relationship between the Mean Thermal Sensation Vote (MTSV) and PET values. The results found that, the neutral sensation PET temperatures (MTSV=0) of outdoor and semi-outdoor spaces were 27.1 °C and 28.5 °C, respectively. And the acceptable thermal conditions (by ASHRAE Standard 55 corresponded with minimum standard of 80% acceptability) ranges were 31.0-23.1°C (difference, 7.9°C) and 32.0-22.4°C (difference, 9.7°C), respectively. Compared with the thermal acceptable range between both spaces was found that the thermal acceptable range in the semi-outdoor environment is much higher than the outdoor environment, indicating that occupants in different spaces have different thermal requirements. The results of corresponding neutral acceptability temperatures for outdoor and semi-outdoor environments were 27.0°C and 27.2 °C, respectively. Compared with the neutral temperature differentiation in terms of sensations and acceptability temperatures for the both outdoor and semi-outdoor environments were 0.1°C and 1.3 °C, respectively. The results demonstrated that occupants of semi-outdoor spaces expect more unacceptable neutral thermal conditions than occupants of outdoor spaces. Thus, the comparison results can be explained that occupants who considered their thermal environments in semi-outdoor environment difficult to control are accepting of thermal environment conditions in summer, even if they are feeling comfort. Based on the results of thermal sensation and acceptability analysis in this study can contributes toward creating and improving comfortable urban spaces in hot-humid contexts to enhance the quality of urban life and achieving a liveable city in tropics such as Chiangmai.
Visitor perception of thermal comfort in two contrasting public landscape gardens during extreme heat events
Monash University, Australia
Previous work on outdoor human thermal comfort has focused on local residents. Our study examines the differences in thermal perception between local residents and international visitors to botanic gardens. This information is important because it improves researcher understanding of tourism climatology. In addition, our study analyses visitor thermal perception stratified by postcode, that reveals the impact of acclimatisation. Data gathered during the Australian summer of 2013/2014 included visitor surveys and meteorological data. During that summer 2204 and 1122 visitors were surveyed in the Royal Botanic Gardens (RBG) Melbourne (a large heavily irrigated traditional botanical garden with many exotic species) and Cranbourne (a large, mostly un-irrigated native garden) respectively. Furthermore, a network of 11 automatic weather stations was established in both gardens during the summer season (18 December 2013 to 26 March 2014). A mobile weather transect was also maintained using the “Garden Explorer” in the RBG Cranbourne. Our study shows that thermal perception is different between local residents and foreign tourists. In particular, European tourists felt hotter than Australian and Chinese visitors in the RBG Melbourne. Moreover, local residents differed in their thermal perceptions between those who visited the RBG Melbourne and Cranbourne. This difference is likely due to the different garden designs and microclimates between the two gardens, even though the weather conditions were similar. As the fieldwork involved multiple heatwave days exceeding 40 °C, it provides new insight into the thermal perception of visitors from different countries of origin under very hot conditions. This information can inform garden landscape succession planning to incorporate thermal comfort in urban planning.
Impact of urban morphology on microclimatic conditions and outdoor thermal comfort – a study in mixed residential neighbourhood of Chennai, India.
SATHYABAMA UNIVERSITY, India
The urban built geometry alters the microclimate significantly which in turn affects the outdoor thermal comfort. The outdoor thermal comfort depends on the ability of the materials to absorb solar radiation (albedo) and the geometrical arrangement of the buildings and its morphology. The aim of this study is to investigate the influence of the built geometry and its morphology on the outdoor thermal environment in a mixed residential neighborhood in the hot humid city of Chennai. The study is twofold. Firstly, the impact of built geometry on the microclimatic conditions was assessed through field measurements and secondly a questionnaire survey on thermal sensation was conducted to study the subjective response of the users to the outdoor thermal environment. The field measurements included the monitoring of meteorological parameters such as air temperature Ta, relative humidity RH, wind speed v and mean radiant temperature Tmrt. Outdoor thermal comfort conditions were assessed through the physiologically equivalent temperature (PET) index, at different built morphology. The influence of various built parameters such as Sky view factor (SVF), street geometry/ aspect ratio, building materials, green cover, etc., on microclimatic conditions and the thermal sensation were assessed. This study also attempts to identify the appropriate urban morphology to improve pedestrian comfort conditions in the hot humid city of Chennai.
Outdoor thermal comfort under photovoltaic canopies – a seasonal field study at Arizona State University
Arizona State University, United States of America
Shade plays an important role in designing pedestrian-friendly outdoor spaces in desert cities. To improve thermal comfort through shading at a pedestrian mall, Arizona State University (ASU) set up three 10 m high photovoltaic canopy structures on its Tempe campus next to the busiest central hub of student life, the Memorial Union (MU). The goal of this research is to quantify the impact of the installed photovoltaic canopies on microclimate and thermal comfort at the mall, using field observations and surveys. Our main objectives are threefold: (1) assess outdoor thermal comfort under photovoltaic canopies and in unshaded locations in a desert urban environment for different seasons and times of day; (2) investigate the relationship between measured and perceived comfort; (3) explore the determinants of thermal sensation, including non-climatic factors.
We installed six stationary, shielded temperature and humidity sensors underneath ASU’s photovoltaic canopies next to the MU and in nearby sun-exposed and tree-shaded locations, logging at a frequency interval of 5 minutes for a full year. Additional transect measurements were conducted hourly from 7:00 AM to 10:00 PM during a typical day in each season under clear and calm weather. Observations underneath the stationary sensors included globe temperature, Wet Bulb Globe Temperature (WBGT), wind speed, solar radiation, and surface temperature. During the transect observations, more than 1000 people were surveyed in the shade and sun close to the stationary sensors about their thermal comfort, perception, preference, recent sun exposure, activity, and adaptation level. We calculated Mean Radiant Temperature (MRT) and comfort indices from the microclimate observations to statistically link thermal sensation votes and perceived comfort to the thermal environment. We explored correlations between survey responses and the thermal environment and investigated the relative significance of environmental, personal, and psychological factors for all seasons, different times of day, and in shaded and unshaded locations. This study will give insight into the relative importance of climatic and non-climatic factors that drive thermal comfort and highlights the importance of shade for the design of more walkable outdoor spaces in desert cities.