Hot-humid Areas Research Articles

Impact of ENVI-met-Based Road Greening Design on Thermal Comfort and PM2.5 Concentration in Hot–Humid Areas

Road greening markedly impacts road thermal comfort and air quality. However, previous studies have primarily focused on thermal comfort or PM2.5 individually, with relatively few addressing both aspects comprehensively, particularly in humid regions. This study combined field measurements and simulations. It employed physiological equivalent temperature (PET) and quantified the horizontal distribution of particulate matter 2.5 (PM2.5). The research examines the effects of planting spacing, tree species, and tree–shrub combinations on pedestrian walkways in humid climates during both summer and winter. Using measured tree data and road PM2.5, a plant model was established and pollution emission parameters were set to validate the effectiveness of the ENVI-met through fitting simulations under various scenarios. The results indicated that (1) plant spacing for trees influenced both the road thermal environment and PM2.5 levels. Smaller spacing improved thermal conditions but increased PM2.5. (2) trees with large canopies and high leaf area indices (LAIs) notably enhanced thermal comfort, while those with smaller canopies and dense understories facilitated PM2.5 dispersion. The 3 m spacing resulted in a maximum absolute PM2.5 concentration difference (C) of 5.05 μg/m3 in summer and a maximum mean absolute PM2.5 concentration difference (M) in the downwind region of 2.13 μg/m3 in winter. (3) Combining trees with shrubs moderately improved pedestrian thermal comfort. However, taller shrubs elevated PM2.5 concentrations on walkways; heights ranging from 1.5 m to 2 m in summer showed higher C values of 5.38 μg/m3 and 5.37 μg/m3. This study provides references and new perspectives for the optimization of roadway greening design in humid areas in China.

Investigation of Bus Shelters and Their Thermal Environment in Hot–Humid Areas—A Case Study in Guangzhou

Investigation of Bus Shelters and Their Thermal Environment in Hot–Humid Areas—A Case Study in Guangzhou

Hygrothermal resilience of typical lightweight steel-framed wall assemblies in hot-humid areas under future climate uncertainty

Ensuring the hygrothermal performance of lightweight steel-framed (LSF) wall assemblies is critical for the sustainability of LSF buildings in hot-humid regions; however, climate change poses new challenges. Therefore, this study aimed to bridge the gap in understanding the characteristics of hygrothermal load changes and the hygrothermal resilience of different LSF wall assemblies. Future climate data for each decade of this century (from 2030 to 2090), under various carbon emission scenarios, were generated based on a typical meteorological year (TMY) for hot-humid areas to evaluate the impact of climate change on hygrothermal loads. The hygrothermal resilience of four typical LSF wall assemblies, with either ventilated rainscreen cladding or face-sealed stucco cladding, with or without external insulation, was evaluated through simulation and comparative analysis. The results indicated that the thermal load would increase with increasing carbon emissions and over time, with the annual average external temperature peaking at 25.8 °C by the end of this century. The frequency of months with a high or critical moisture load would increase, although the moisture load may fluctuate across scenarios and years. Consequently, the cooling and dehumidification loads may increase by 52–60 % and 40–88 %, respectively. The hygrothermal risk within the walls may increase, with maximum increases of 2.8–8.0 % in the annual average relative humidity, 2.7–3.0 °C in the annual average temperature, and 10–35 % in the wetness duration. However, the impacts could be reduced by using ventilated rainscreens and external insulation, with further precautions needed to mitigate the increasing hygrothermal risk in areas with thermal bridges and rainwater leakage, as well as at the outer interface of the external insulation. These findings could provide a reference for the design of LSF buildings adapted to climate change in hot-humid areas.

Assessing the winter indoor environment with different comfort metrics in self-built houses of hot-humid areas: Does undercooling matter for the elderly?

Thermal comfort in housing is vital for well-being. Despite hot and humid regions experiencing shorter cold periods compared to heatwaves, vulnerable populations are susceptible to threats from cold snaps. However, existing research overlooks undercooling risks in hot regions during winter. This study examines self-built houses in densely populated, hot and humid areas, mainly occupied by elderly residents. We conducted an on-site measurement recording hourly indoor air temperature, humidity, and black globe temperature during wintertime. Two thermal comfort metrics (aPMV and adaptive regression model) and two resilience metrics (SET degree-hour, Hours of Safety) were used to quantify thermal conditions during cold periods under current and future climate conditions. The results show that undercooling hours in recent years exceed 90 % of wintertime using aPMV index and adaptive regression models. Under future climate scenarios (Representative Concentration Pathways), undercooling hours only decrease by 10 %–25 % from 2020 to 2100 across all metrics. Extreme cold events in 2018 saw SET degree-hours double the thermal resilience threshold, while they pose health risks to the elderly for up to 21 days according to the HOS metrics. This study aims to identify the importance of addressing winter thermal comfort in hot and humid regions and to assess the risk posed by cold snaps to vulnerable populations. By quantifying these risks, the study contributes to better decision-making regarding hot-humid region housing thermal retrofit strategies for architects, engineers, and other stakeholders.

Comprehensive analysis on the thermal comfort of various greening forms: a study in hot-humid areas

The potential impact of greening on improving thermal environments is widely recognized. However, few studies have comprehensively evaluated the influence of different forms of greening, such as various tree crown widths, green facades, green roofs, and their combinations, on both outdoor and indoor environments. In this study, we conducted an extensive investigation within a residential precinct at Guangzhou University by combining on-site measurements and numerical simulations with the ENVI-met model. Physiologically Equivalent Temperature (PET) and Temperature Humidity Index (THI) were used to assess outdoor thermal comfort. The results indicated that planting trees had a greater impact on improving the outdoor thermal environment than green facades and green roofs, and this effect increased with the crown width of the trees, with a maximum potential reduction of 4.8 °C (0.2 °C) in PET (THI). Green facades can bring a change of up to 101.9 W m−2 in sensible heat flux, resulting in a reduction of up to 1.8 °C in indoor Ta (air temperature). Conversely, green roofs composed of grass exhibit minimal effects in both outdoor and indoor environments. Finally, we provide recommendations for the construction and renovation of projects in residential areas, with a focus on hot-humid areas.

Mist Spraying as an Outdoor Cooling Spot in Hot-Humid Areas: Effect of Ambient Environment and Impact on Short-Term Thermal Perception

Mist spraying is an active cooling technology used to alleviate heat stress during hot summers. However, there is limited experimental research on the relationship between ambient thermal parameters and spray cooling efficiency, as well as the transient and short-term thermal perceptions of local residents. In this study, an intermittent mist spraying system was set up, and environmental measurements, coupled with questionnaire surveys, were conducted under typical high temperature and still air conditions. The aim was to investigate the relationship among environmental factors, spray cooling effects, and dynamic improvements in human thermal perception. The results showed that higher ambient temperatures resulted in a more significant cooling effect, with a maximum value of 5.68 °C. Upon entering the spraying area, people experienced a large perceptual change, with the mean thermal sensation and thermal comfort change covering 73% and 62% of the total change ranges, respectively. This study indicated that the mist spray system can be activated if the ambient temperature exceeds 32.5 °C, helping local residents maintain a physiological state close to slightly hot and neutral comfort. These findings suggest that mist spraying can be applied in environmental design as an outdoor cooling spot to mitigate urban overheating, providing valuable insights for the application of mist spray systems in actual outdoor settings in hot-humid areas.

Effects of thermal perception on restorative benefits by green space exposure: A pilot study in hot-humid China

Green space exposure can bring various psychological restorative benefits, including attention restoration, stress recovery, and mood improvement. However, most research on restorative environments has focused on visual and acoustic experiences. The role of thermal perception in psychological restoration has been largely overlooked. Based on a pre-test-post-test design intervention experiment in an urban park in Guangzhou, China, this study investigated the relationship between thermal perception and the psychological restorative benefits of three types of green space in hot-humid areas. Thirty-eight university students participated in this experiment, each engaging in three environmental stimuli. The results showed that: 1) short-term exposure to urban park grassland and forest in hot and humid areas significantly increased the Perceived restorativeness scale (PRS) score and decreased negative emotions, for example, Anger. 2) Thermal Comfort Vote (TCV) significantly predicted the PRS score. 3) The type of green space greatly influenced the effect of TCV on PRS. These findings prove the relationship between thermal perception and the restorative benefits of green space exposure. The study further integrates the research areas of urban climate, green exposure, and psychological restoration. Incorporating thermal perception and psychological restoration concepts in urban green spaces' design and management helps enhance comfort and psychological well-being.

The Multi-Objective Optimization Design and Hydrothermal Performance Evaluation of Anhydrous Calcium Sulfate Whisker and Polyester Fiber Compound Modified Asphalt Mixture in Hot-Humid Areas.

In hot and humid climates, asphalt pavements frequently encounter environmental factors such as elevated temperatures and rainfall, leading to rutting deformations and potholes, which can affect pavement performance. The primary objective of this study was to enhance the hydrothermal characteristics of asphalt mixtures through an investigation into the impact of anhydrous calcium sulfate whisker (ACSW) and polyester fiber (PF) on the hydrothermal properties of asphalt mixtures. In this paper, a central composite concatenation design (CCC) was employed to determine the optimal combination of ACSW and PF contents, as well as the asphalt aggregate ratio (AAR). Each influencing factor was assigned three levels for analysis. The evaluation indexes included dynamic stability, retained Marshall stability, and tensile strength ratio. Using the analysis methods of variance and gray correlation degree analysis, the hydrothermal properties of the asphalt mixture were examined in relation to the contents of ACSW, PF, and AAR based on the CCC results. Consequently, the optimal mix design parameters for composite modified asphalt mixture incorporating ACSW and PF were determined. The results indicated that the asphalt mixtures with hydrothermal qualities exhibited optimal performance in terms of 4.1% ARR, 11.84% ACSW, and 0.4% PF. The interaction between AAR and ACSW content had a greater effect on the dynamic stability and tensile strength ratio of the asphalt mixture, whereas the incorporation of ACSW and PF had a greater effect on the retained Marshall stability of the asphalt mixture. Among the three contributing factors, AAR exhibited the strongest relationship with the hydrothermal characteristics of the asphalt mixture, followed by the ACSW content; the correlation of PF content was the lowest. Therefore, to enhance the hydrothermal characteristics of the asphalt mixture, it is important to conduct a full evaluation of the constituents of ACSW and PF, along with the AAR in hot-humid regions.

Modeling of cotton dust effects using indigenously designed experimental setup for solar powered textile industry in Pakistan

ABSTRACT The performance improvement of solar photovoltaic (PV) systems is envisaged to be one of the prime concerns for today’s energy sector to ensure optimal power yield. This paper investigates the impact of cotton dust on the solar-powered PV plant in the textile industry. In the first stage, using HM3301, the hourly data of cotton dust (6759 µg/m3) has been collected from an installed 250 kW system of a textile industry located in the hot-humid area of Pakistan. In the second stage, to model the same collected data, an indigenous experimental chamber has been constructed. The chamber has been designed to facilitate the fixed and moveable PV module. In the former type, the panel orientation was fixed at 30°, while the later configuration incorporates the moveable module that rotates with respect to the sun rotation. The experiment has been conducted for 96 hours spread over 12 days for each configuration, which collects the hourly data of humidity, temperature, voltage, current, and dust through five different dedicated sensors. The observed results show that the power output from the fixed PV configuration is 5.32% lesser than the movable configuration. PV panel power output efficiency of fixed configuration decreases from 0.134% to 0.102%. Similarly, the power output efficiency of movable PV module decreases from 0.147% to 0.115%.This illustrates cotton dust reduces the power output greater in fixed configuration as compared to movable configuration. Furthermore, linear regression analysis has been used on acquired data of power output and cotton dust accumulation that shows both quantities are highly correlated up to 97.6% and 95.1%, respectively. Also, by using the regression equation maximum quantity of cotton dust has been computed, which shows 0.116 grams for fixed and 0.129 grams for moveable configuration that will minimize the power output of the PV module. Through this study, textile units can devise periodic cleaning and assessment patterns that will help to maintain the power output and increase the life of the PV power plant.

Adaptation-based indoor environment control with night natural ventilation in autumn in an office building in a hot-humid area

In hot-humid areas, the temperature is high during the daytime in autumn which causes dissatisfactory thermal sensation and large cooling energy consumption. Night ventilation (NV) is an effective method that utilizes lower outdoor temperature at night to pre-cool buildings. Adaptation models are widely accepted physics-based comfort models and are practical for indoor environment control. However, the potential of NV in adaptation-based control has not been fully studied yet. In this study, we proposed a new adaptation-based control with NV towards autumn scenarios in hot-humid areas. We implemented the proposed control based on an existing system and tested its performance in an office building. Three modes, i.e., the conventional mode, the adaptation-based control without NV, and the adaptation-based control with NV, were evaluated and compared. The results showed that compared with the conventional mode, the humid sensation in the adaptation-based control without NV was close to neutral. The airflow perception was stronger. The CO2 concentration was maintained within normal level. The average daily energy consumption was decreased by 76%, but most occupants felt slightly warm. With NV, the indoor air temperature and the mean radiant temperature decreased. The occupants’ thermal sensation was close to neutral. The average daily energy-saving rate increased to 97%. This study was the final step of a series of studies on adaptation-based controls in hot-humid areas. These studies applied theoretical adaptive models to practical on-site controls and demonstrated the potential for improving human comfort and energy efficiency by the proposed adaptation-based controls.

The impact of tree species and planting location on outdoor thermal comfort of a semi-outdoor space.

Previous studies have shown that tree arrangement provides effective regulation of the outdoor thermal environment and combats the urban heat island (UHI) effect. To further explore semi-outdoor thermal environment improvement using tree arrangement, we selected two common arbor species from Guangdong Province, namely, Lagerstroemia speciosa and Bombax ceiba. We discuss the influence of courtyard tree arrangements on the thermal environment of semi-outdoor spaces (courtyards and overhead spaces) of a teaching building in a hot-humid area. The ENVI-met model was used and verified with field measurements; the universal thermal climate index (UTCI) was used as an index to evaluate the thermal environment of semi-outdoor spaces. We found that (1) adjusting the distance between trees and buildings reduced the UTCI values by 0.4 (overhead spaces) and 0.8 ℃ (courtyards); and (2) when the distance between the arbor and the building is fixed, the UTCI values of arranging Lagerstroemia speciosa can be reduced by up to 0.5 (overhead spaces) and 1.0 ℃ (courtyards) compared to that of Bombax ceiba; this study provides practical suggestions for the layout of trees in semi-outdoor spaces of teaching buildings in the hot-humid areas of China.

Influence of space properties of enclosed patio on thermal performance in hot-humid areas of China

Patio plays an important role in climate adaptation and microclimate adjustment of buildings. This study aims to explore enclosed patio design guidelines, which are essential for both architectural design methodology and practical projects for providing better thermally comfortable indoor and outdoor spaces. A combined qualitative and quantitative methodological approach was used to clarify how the passive design strategies of the enclosed patio affect the thermal environment of houses around the patio. The findings reveal the spacial characteristics and thermal adjustment of enclosed patios. The results of simulation indicate that appropriate design parameters of enclosed patio can achieve a better indoor and outdoor thermal comfort environment for its users, which includes similar dimension in width and depth, increased number of windows in a high ratio of width to depth, semi-open auxiliary space, 3-4 floor height, upper-lower double windows of four-sided enclosed patio and south opening direction of three-sided enclosed patio.

Spray optimization to enhance the cooling performance of transparent roofs in hot-humid areas

Spray cooling was regarded as an effective technique for outdoor cooling but its application to transparent roofs is still limited, owing to the absence of an explicit system design. In this study, the influence of three spray nozzle types with six modes on the spray cooling performance of glass curtain samples that belong to one transparent roof was first determined by a test device. Thereafter, the spray system, designed based on the selected nozzles, was assembled on the transparent roof inside a laboratory building. The thermal property moderation of the roof and indoor environment and the corresponding cost effectiveness generated by this system were further assessed. The results revealed that the spray system could effectively cool glass curtains. Compared to water-spray, mist-spray can achieve a better cooling and shading effect by shaping more dispersed and smaller droplets that effectively enlarge the contact areas with the targeted surface. The exterior glass surface temperature generated by the mist-spray was 8.0 °C lower than the surrounding air temperature, and the solar transmittance ratio decreases up to 14% compared to dry conditions. Field experiments further revealed that the mist-spray system could noticeably mitigate indoor overheating and further eliminate thermal stratification among different floors. Air temperature 10 cm below the interior roof surface and black-globe temperature of 1.5 m higher on the third floor demonstrated a decrease of up to 10 °C and 8.9 °C, respectively. The air temperature gap between these three floors decreased to approximately 4 °C. Furthermore, owing to the mist-spray system, a total of 24.36 kW∙h of energy saving was realized during the experiment and the general infrastructure investment could be recovered within 6.26 years. This study is of great significance for promoting the scientific practice of the mist-spray technique to enhance the building thermal performance.

Hygrothermal performance optimization of lightweight steel-framed wall assemblies in hot–humid regions using orthogonal experimental design and a validated simulation model

As a layered construction, lightweight steel-framed (LSF) wall assemblies are applicable to different climates and used worldwide. Due to ill-informed construction and material designs, moisture-related durability problems occur, especially in hot–humid areas. Here, a hygrothermal simulation model of typical LSF wall assemblies was validated, and the influences of six construction layers (each with three sets of parameters) on the overall properties and performance were investigated via orthogonal experimental design (OED). Each layer exhibited various impact trends and contribution ratios at different positions. To reduce moisture risks, LSF wall assemblies should generally prevent the infiltration of outdoor moisture as much as possible while strengthening the inward drying capacity. The optimal configuration should comprise multiple water and vapour barriers with a ventilated layer, external insulation, permeable cavity insulation and interior sheathing board with a finish. Finally, this optimization method comprising the hygrothermal simulation and OED techniques could be applied to the hygrothermal performance of LSF wall assemblies under certain climatic conditions.

Effects of Tree Arrangement and Leaf Area Index on the Thermal Comfort of Outdoor Children’s Activity Space in Hot-Humid Areas

Hot-humid areas have long, hot summers and poor outdoor thermal comfort (OTC). The urban heat island (UHI) effect exacerbates the deterioration of OTC in hot-humid areas, seriously affecting the thermal safety of children’s outdoor activities. In this study, 60 scenes were simulated using ENVI-met based on different leaf area index (LAI) and planting arrangements to explore how tree LAI and planting arrangements affect the small-scale thermal environment during hot summer months and to assess OTC using the Universal Thermal Climate Index (UTCI). The research shows that (1) high LAI trees optimize OTC more than low LAI trees, but low LAI trees can be planted multiple times to achieve the level of optimization of high LAI trees; (2) increasing the number of trees optimizes the OTC of the study area, reducing the UTCI by up to 3.7 °C with increased planting compared to unshaded areas; (3) thickening the shade in the east–west direction optimizes the OTC of the study area more than thickening the shade in the north–south direction, with too much north–south shade optimizing the OTC of the study area by only 0.01%. This study provides practical advice for the design of planting in outdoor CAS in hot-humid areas.

Evaluation of Passive Cooling and Thermal Comfort in Historical Residential Buildings in Zanzibar

Indoor thermal comfort is essential for occupants’ well-being, productivity, and efficiency. Global climate change is leading to extremely high temperatures and more intense solar radiation, especially in hot, humid areas. Passive cooling is considered to be one of the environmental design strategies by which to create indoor thermal comfort conditions and minimize buildings’ energy consumption. However, little evidence has been found regarding the effect of passive cooling on the thermal comfort of historical buildings in hot–dry or hot–humid areas. Therefore, we explored the passive cooling features (north-south orientation, natural ventilation, window shading, and light color painted walls) applied in historic residential buildings in Zanzibar and evaluated the residents’ thermal responses and comfort perception based on questionnaires and field surveys. The results showed that the average predicted mean votes (PMVs) were 1.23 and 0.85 for the two historical case study buildings; the average predicted percentages of dissatisfaction (PPD) were 37.35% and 20.56%, respectively. These results indicate that the thermal conditions were not within the acceptable range of ASHRAE Standard 55. Further techniques, such as the use of lime plaster, wash lime, and appropriate organization, are suggested for the improvement of indoor thermal comfort in historical buildings in Zanzibar. This study provides guidelines to assist architects in designing energy-efficient residential buildings, taking into account cultural heritage and thermal comfort in buildings.

A modified method of the standard effective temperature (SET) based on the extended mean skin temperature index (EMSTI)

Among the existing thermal environment evaluation indexes, the standard effective temperature (SET) is based on the two-node model and performs better than the predicted mean vote (PMV) in non-neutral environments. However, previous studies show that the mean skin temperature and skin wettedness of the SET standard environment do not equal to the actual value, which violates the premise of SET. Moreover, it is found that the mean skin temperature of the standard environment differs from the actual value significantly under high temperature and humidity. Therefore, the applicability of SET in hot and humid environments deserves further study. The mean skin temperature is a superior evaluation index of thermal sensation in steady-state thermal environments with moderate temperature and humidity, and has been widely used in thermal sensation prediction. However, there also lacks in-depth research on the relationship between thermal sensation and mean skin temperature under high temperature and humidity. In this study, an extended mean skin temperature index (EMSTI) based on mean skin temperature combined with the maximum latent heat loss from skin surface is proposed through theoretical derivation. By verifying the index using the experimental data from different laboratories, it is shown that the proposed EMSTI can well evaluate the thermal sensation of hot and humid environments in different areas. The EMSTI is further used to represent thermal sensation to establish the equivalent relationship between the standard and actual environment, and the SET in hot-humid areas is modified.

Effects of Tree Species and Layout on the Outdoor Thermal Environment of Squares in Hot-Humid Areas of China

Planting trees is an effective way to regulate the outdoor thermal environment and combat urban heat islands (UHIs). Tree species and layout can have a considerable effect on, for example, the outdoor shading and wind fields, and finally the distribution of the occupant thermal sensations in outdoor spaces. We studied the influence of common tree species and layouts on the outdoor thermal environment under typical summer and winter weather conditions in the hot–humid areas of China. Each arbor model was established by the physical parameters obtained from field measurements. Physiological equivalent temperature (PET) was used to evaluate the thermal performance of the outdoor environment. The ENVI-met software was validated with field measurements and then used to assess the outdoor thermal environment under typical summer and winter weather conditions. The results showed the following: (1) Without considering the tree species, the difference in maximum PET values for different planting distances in summer and winter was 1.14 and 2.13 °C, respectively. (2) Planting arbors with different planting methods in inactive spaces had little effect on the thermal environment of the surrounding active space. (3) Arbors with high leaf area density (LAD) values performed better in regulating outdoor thermal comfort than arbors with low LAD values. The maximum differences in PET values of different arbors in summer and winter were 0.98 and 1.37 °C, respectively. This study provides practical suggestions for arbor planting in square spaces in the hot–humid areas of China.

Comprehensive analysis on the energy resilience performance of urban residential sector in hot-humid area of China under climate change.

Residential sector is one of the main consumers of the energy market. This study conducts a comprehensive analysis on the future energy resilience performance of urban residential sector in hot-humid area of China in the 21st century. Uncertainties, including future climate, building characteristic and occupancy behavior, are considered in future energy projections. Since the local climate is characterized by hot summer and warm winter, and local building energy is cooling-dominated, this study focuses on the changes in future cooling load. The results indicate that future energy demand of residential sector in hot-humid areas will increase over time except under the Shared Socioeconomic Pathway (SSP) 1-2.6, and the magnitude of the rise could be significant. Under the SSP5-8.5, the most severe scenario for climate change, the average annual energy demand of residential sector in the long-term future is about 90 kWh/m2, which is above twice the energy demand under current typical climate. The annual building energy fluctuates more in a hotter future. Energy demands of dwellings with different building forms and use patterns may vary disproportionately in the changing climate. The framework and findings could give implications on future energy system design in cities.

Improving the Thermal Comfort of an Open Space via Landscape Design: A Case Study in Hot and Humid Areas

Hot and humid areas experience constant high temperatures and high humidity during summer, causing widespread concern about outdoor thermal discomfort. This paper investigates the effects of landscape design strategies on outdoor thermal environments during typical summer and winter weather conditions in the hot–humid areas of China. The physiological equivalent temperature (PET) is used for evaluating the thermal performance of the proposed outdoor environments. ENVI-met software was validated via field measurements for this study and was used to evaluate the outdoor thermal environment under typical summer and winter weather conditions. Three kinds of common landscape elements were analyzed: tree species, pavement, and water bodies. The results show that (1) by properly arranging landscape elements, the PET can be reduced by up to 1.6 °C in summer without sacrificing relevant thermal comfort during winter. (2) Arbors with high leaf area density (LAD) values performed better than those with a low LAD value for improved outdoor thermal comfort. (3) The influence of pavement on outdoor thermal comfort differs when under conditions with and without shade. This study provides practical suggestions for landscape design in open spaces within hot–humid areas.