Urban Microclimatic Conditions Research Articles

Assessment of Outdoor Thermal Comfort in Urban Public Space, during the Hottest Period in Annaba City, Algeria

In this study; the outdoor thermal comfort of the users of two urban plazas with different morphologies in Annaba city, Algeria, have been evaluated. First, field measurements of the microclimatic parameters took place; namely the air temperature and the relative humidity in the two urban plazas, during hot days. Then, these measurements were compared with the results of the numerical simulations carried out by ENVI-met software in order to validate the model. The outdoor thermal comfort was evaluated by microclimatic measurements as well as a questionnaire survey consisting of interviews during the measurement days. The main objective was to determine the neutral Physiological Equivalent Temperature (PET) and to examine the influence of urban microclimatic conditions on the subjective thermal perception of people, as well as to compare it with different indexes of thermal comfort. Hence, the aim was to compare the microclimatic parameters of the two plazas, with and without vegetation and to see their impact on the thermal comfort indices. The results show that there is a difference between the two morphologies. Moreover, vegetation and urban morphology influence the neutral values of the thermal comfort indices.

A Computational Fluid Dynamics Modelling Approach for the Numerical Verification of the Bioclimatic Design of a Public Urban Area in Greece

Recent recordings of urban overheating reveal a dramatic increase in cities’ population exposure to heatwaves. Heatwaves’ implications are escalated in urban environments due to the intensification of the Urban Heat Island (UHI) effect. To combat the overheating and UHI adverse effects, novel urban rehabilitation actions are needed based on reliable predictions of appropriate Key Performance Indicators (KPIs) (such as pedestrian-level air temperature and thermal comfort) for alternative design scenarios. The objective of the current study is to present the application of a previously developed Computational Fluid Dynamics (CFD) model for the calculation of urban microclimatic conditions for the assessment of the UHI and thermal-comfort conditions in a central urban area in the city of Heraklion in Crete, Greece. Empirical validation of the model is performed through comparisons with monitored microclimate data (i.e., air temperature, relative humidity, wind speed) and actual sensation vote recordings found in another research study. In compliance with the latter, the validation campaign is conducted for a typical hot summer day in July 2009 from 10:00 to 16:00. The model is then used to assess the UHI effects for both the existing urban configuration and a given suggested environmental upgrade of the space. Simulations of the existing situation reveal that the squares located in the studied area already stand for efficient resistances to urban overheating, and heat vulnerabilities are detected mainly in non-shaded traffic and pedestrian roads perimetric to the squares. Based on the CFD simulations, the suggested environmental upgrading plan exhibits a reduction in the peak mean air temperature of 0.46 °C, and thermal comfort is improved by at least 5% (based on SET) throughout the studied area in summer. At the same time, simulations of winter conditions suggest that there are limited potential pedestrian thermal-sensation and building heating penalties under the considered renovation scenario.

Solar energy harvesting pavements on the road: comparative study and performance assessment

• Performance of various solar energy harvesting pavements are compared. • The pavements’ impact on the urban heat island effect is analyzed. • The electricity and heat yields of the pavements are simulated. • The PIPVT module can achieve the average overall energy efficiency of 37.31%. As a significant infrastructure in modern cities, road pavements occupy a great share of urban surfaces and absorb abundant solar radiation. Thus, pavements have tremendous potential in solar energy utilization and can serve as distributed energy generators in smart and sustainable cities. Some solar energy harvesting pavement modules have emerged in recent years, including pavement-integrated photovoltaic (PIPV) module, pavement-integrated solar thermal (PIST) module, and pavement-integrated photovoltaic thermal (PIPVT) module. In this study, for all the above modules, simulations were conducted with the developed and validated two-dimensional transient models on the weather conditions of four typical days in different seasons in Shanghai. Both the operating performance and influence on the urban heat island (UHI) effect were investigated to evaluate and compare their energy performance and effect on urban microclimatic conditions. The results show that the electricity yield of the PIPVT module is slightly higher than that of the PIPV module, while its heat yield is lower than that of the PIST module on all typical days. When considering both electricity and heat yields, the PIPVT module can achieve an average overall energy efficiency of 37.31%. Compared with the conventional pavement module, all three solar energy harvesting pavement modules have lower maximum asphalt average temperatures that can decelerate the thermal aging of asphalt concrete. The PIPVT module has the most significant effect on the reduction of the maximum asphalt average temperature, decreasing it by 10.57°C on average. Additionally, all three solar energy harvesting pavement modules can mitigate the UHI effect, and the PIPVT and PIST modules have the most and the least influence on UHI effect mitigation, respectively.

Building indoor model in PALM-4U: indoor climate, energy demand, and the interaction between buildings and the urban microclimate

Abstract. There is a strong interaction between the urban atmospheric canopy layer and the building energy balance. The urban atmospheric conditions affect the heat transfer through exterior walls, the long-wave heat transfer between the building surfaces and the surroundings, the short-wave solar heat gains, and the heat transport by ventilation. Considering also the internal heat gains and the heat capacity of the building structure, the energy demand for heating and cooling and the indoor thermal environment can be calculated based on the urban microclimatic conditions. According to the building energy concept, the energy demand results in an (anthropogenic) waste heat; this is directly transferred to the urban environment. Furthermore, the indoor temperature is re-coupled via the building envelope to the urban environment and affects indirectly the urban microclimate with a temporally lagged and damped temperature fluctuation. We developed a holistic building model for the combined calculation of indoor climate and energy demand based on an analytic solution of Fourier's equation and implemented this model into the PALM model.

Foraging Behaviour of Heterotrigona itama (Apidae: Meliponini) in Residential Areas

This study aims to investigate the foraging behaviour of Heterotrigona itama in exploiting food resources at a residential area, and the viability of this species to adapt to urban microclimatic conditions. Heterotrigona itama prefers to forage at areas closer to their nesting site, where diverse food sources are found. The marked bees of H. itama prefer to forage on various resources available at a 500-metre radius from the house yard. The obtained results indicate that the active foraging pattern of H. itama is negatively correlated to the time phases of a day (p < 0.05). This phenomenon was contributed by the three peaks of foraging hours, which reached a peak in the early morning (6:30 to 8:00 a.m.), moderately peaked towards the evening (2:30 to 3:30 p.m.), and was greatest towards the afternoon (10:30 a.m. to 12:00 p.m.). The ambient temperature and relative humidity were not the primary factors influencing the average number of foragers exiting from and returning to the hives (temperature, p > 0.05; and humidity, p > 0.05). There was a difference between the varieties of content resources collected by the bees (p < 0.05). The nectar or water sources was the highest material (51.39%) that was brought back to the hive by foragers, followed by resin (34.73%) and pollen (13.87%). There was a significant difference in foraging time phases by returning foragers for collecting resin (p < 0.05) and nectar or water (p < 0.02), but there was no significant difference in foraging time phases found for pollen (p > 0.05). We concluded from the results that H. itama is able to withstand urban microclimate conditions, and successfully incorporated pollen, nectar or water, and resin obtained from floral and non-floral resources into their diet.

Sensitivity analysis of urban microclimatic conditions and building energy consumption on urban parameters by means of idealized numerical simulations

In the present work the mesoscale meteorological model Weather Research and Forecasting (WRF), coupled with a multilayer urban canopy parameterization and a building energy model (BEP + BEM), is used to analyze the sensitivity of both urban climatic conditions and building energy consumption on parameters characterizing urban materials and the building environment. In particular, simulations in an idealized urban area, with different urban geometry and under different climatic conditions, are compared to evaluate the relative importance of various parameters. Results highlight that the target indoor temperature has the strongest impact on both building energy consumption and external air temperature. Building energy consumption is also significantly affected by other internal building parameters, such as the ventilation rate and the heat produced by equipment and occupants. On the contrary, no significant influence, either on building energy consumption or on air temperature, is found from changes in wall albedo and emissivity.

Albedo Quantification Using Remote Sensing Techniques. Cool Roof in the Metropolitan Area of Mendoza-Argentina

The presence of cities raises air temperature. The growth of sealed urban surfaces and anthropogenic heat modifies the natural energy balance increasing the CO2 emissions of a city. A strategy to reduce urban temperatures and energy consumption is the widespread application of cool materials -with high albedo and high emissivity- in the urban envelope. Roofs are the horizontal opaque surfaces most exposed to solar radiation and are therefore the ones that absorb the highest thermal load of a building. The objective of this research is to design a procedure that allows the discrimination the different roofing materials within the Metropolitan Area of Mendoza, Argentina, to determine the possible energy savings and improvements in urban microclimatic conditions associated with the increase of albedo in the roofs of the city. The methodology is based on a supervised classification of roof materials using spectral signatures with QGIS 3.2 ‘Bonn’ software. For this purpose, images from the Sentinel 2a platform were used and 3 series of spectral signatures were obtained from built urban areas. The results show that the materials mainly used in the roofs of the city of Mendoza are membranes (74%), zinc sheet (14%) and traditional tiles (13%). These findings represent an efficient tool to quantify the energy and environmental effects of regulating albedo values in urban roof.

Synergetic urban microclimate and energy simulation parametric workflow

Although the interrelations between urban microclimates and energy demand have been acknowledged, few workflows integrate microclimatic boundary conditions to predict energy demand in parametric morphological studies. This paper helps bridge this gap by introducing a novel workflow which brings together energy and microclimatic modelling for a synergetic assessment at the block scale. The interrelation between form, energy and urban microclimatic conditions is explored here in the climatic context of Tel Aviv by coupling Envimet and EnergyPlus. The potential of this coupling is explored in three different block typologies, each tested for four different density scenarios focusing on the cooling demand on a typical hot day. Results show the substantial increase of as high as 50% in cooling demand when the microclimatic weather data is taken into account and indicate the potential to capitalize on new computational tools which allow to quantify the interrelations between urban form, microclimate and energy performance more accurately.

Interpreting air temperature generated from urban climatic map by urban morphology in Taipei

The intense development of Taipei City has caused high thermal stress in its urban areas. This study used the urban climatic map (UCmap) and the local climate zone (LCZ) to analyze how land development patterns have affected urban thermal conditions. The UCmap is an efficient tool for obtaining information about urban microclimatic conditions based on urban development parameters and the map provides urban planners with information to mitigate the growing problem of thermal stress. The LCZ is system for classifying urban morphology including land cover, buildings, and vegetation, which can be used to relate land patterns to climate conditions. The results of this study indicate that combining UCmap and the LCZ is helpful for assessing thermal conditions in urban areas, and this approach can be used in many cities to determine the most suitable built environment for mitigating thermal stress.

Comparison between simplified and detailed EnergyPlus models coupled with an urban canopy model

This paper gives practical information related to the use of simplified EnergyPlus models and its impact on estimates of the cooling demand, especially when EnergyPlus models are coupled with an urban canopy model. By simplified models, it is referred to shoebox as well as multi-floor models. For the interest of climatologists, their influence on estimates of urban temperature and specific humidity is also studied. To explore divergences between the use of detailed and simplified EnergyPlus models, a typical office area in Singapore is selected as a case study. As a result, it is observed that the use of multi-floor models provides estimates of the cooling demand and urban microclimatic conditions which achieve the best agreement with these assessed from detailed models. On the other hand, less time is required to run a shoebox than a multi-floor model. Although these outcomes are inferred from an excellent case study, further research must be conducted on several types of urban areas to elaborate a general theory.

Investigation of PMV Model for Evaluation of the Outdoor Thermal Comfort

Urban microclimatic conditions affect human body energy balance and individuals’ thermal perception. Therefore, it is necessary to find an appropriate index to evaluation of outdoor space. Predicted Mean Vote (PMV) always use for evaluation of outdoor thermal environments. However, PMV model was developed based on the indoor chamber experimental data. Therefore, there is a need to compare in detail based on the outdoor survey data. A field survey has been conducted in Guangzhou this summer. The results show that there is a strong linear relationship between the PMV and operative temperature. However, the relationship between the TSV and operative temperature is not clear. At the lower operative temperature range of, 28 -36 °C, TSV increases with rising of operative temperature. When operative temperature is higher than 36 °C, TSV concentrates on the range of 2.5 – 4.0. In addition, the difference between PMV and TSV is not significant at the range of 28 – 34 °C. At the higher operative temperature, the prediction of PMV is not corrective. Based on the statistics, the adaptive thermal comfort model is developed, which is validated by the survey data with a small error.

Thermal perception of outdoor urban spaces in the hot arid region of Cairo, Egypt

Urban microclimatic conditions affect the human body energy balance and individuals’ thermal perception; which in turn influences their usage of outdoor spaces. This study investigates users’ thermal comfort in an urban street in a hot arid climate of Cairo, Egypt. The investigation was carried out in two different climatic conditions; summer and winter, using subjective surveys on the perception of the thermal environment applying the seven-point ASHRAE 55 thermal sensation votes (TSV). The survey is complimented by a one week of field measurements in both seasons to examine the main climatic parameters affecting thermal comfort in term of psychological and personal factors. The thermal acceptability by means of thermal sensation votes was assessed based on physiologically equivalent temperature (PET). Analytical results indicate that the thermal comfort ranges were between 23 and 32°C PET while the preferred temperatures were 29°C PET in summer and 24.5°C PET in winter. These values were higher than that of the temperate climates and European scale, confirming the existence of thermal adaptation and indicating that the physical environment and the psychological adaptation is argued to be complementary rather than contradictory, and consideration of this duality could increase the use of the city's open spaces.

Quantification of thermal bioclimate for the management of urban design in Mediterranean climate of Barcelona, Spain.

In order to contribute to the sustainability of the outdoor environment, knowledge about the urban thermal bioclimate should be transferred into climatic guidelines for planning. The general framework of this study responds to the need of analyzing thermal bioclimate in Mediterranean climate regions and its influence as an urban design factor. The paper analyzes the background of the urban climate and thermal bioclimate conditions in Barcelona (Spain), through the effect of shade conditions and wind speed variations. Simulations of shade and wind speed variations were performed to evaluate changes in thermal bioclimate due to modifications in urban morphology. Air temperature, relative humidity, wind speed, and solar radiation for the period from January, 2001 to January, 2015 were used to calculate physiologically equivalent temperature (PET) using the RayMan model. The results demonstrate that shade is the most important strategy to improve urban microclimatic conditions. In Barcelona, human thermal comfort conditions can be improved by shade and wind speed increase in terms of PET above 23°C and by a wind speed decrease for thresholds of PET below 18°C. Heat stress situations can be mitigated by shade and wind speed increase in conditions above 35 and 45°C, respectively. The results of the study are an important contribution for urban planners, due to their possibilities and potential for the description of microclimatic conditions in Mediterranean climate regions. The knowledge is useful for improved human thermal comfort conditions, from the suitable configuration of urban form and architecture.

Bioclimatic design of open public spaces in the historic centre of Tirana, Albania

Abstract The aim of this paper is to study the urban micro-climatic conditions in the historic centre of Tirana in order to integrate the information in the rehabilitation of specific open spaces. The process included field measurements of the thermal characteristics in the examined area, bioclimatic design and use of passive cooling techniques (cool materials, green spaces, water, solar control & earth to air heat exchangers). Advanced simulation tools were used to evaluate and optimize the planed microclimatic modifications. CFD calculations with model PHOENICS have been applied for the simulation of the air flow and the temperature field at the concept design stage. The proposed design solutions included the increase of vegetation (planting of trees), the use of shading, as well as the use of cool materials with appropriate thermal and optical properties. In parallel, earth to air heat exchangers, are proposed to supply cool air during the summer period and preheat the ambient air during the winter. Simulations have shown that the use of the proposed bioclimatic measures can decrease the peak summer ambient temperatures up to 3 °C, while surface temperatures are decreased seriously. In parallel, the calculation of appropriate bioclimatic indices showed that the thermal comfort conditions were significantly improved with the application of interventions mainly because of the increase of shading as well as because of the use of construction materials with high emissivity and reflectivity values.

Effect of urban morphology on wind condition in idealized city models

Wind conditions in urban environments are important for a number of reasons. They can serve to transport air pollutants out of the urban environment and to moderate urban microclimatic conditions if satisfactory, yet can compromise pedestrian comfort and safety if not. We aim to study experimentally and numerically the effects of urban morphology (e.g., overall city form (skyline), street orientation, and street configuration) on wind conditions in cities. This report considers our initial investigations of two idealized city forms that are coincidentally similar to ancient Roman cities that were organized on one or two primary streets – a main north–south street, the cardus maximus, and a secondary east–west street, the decumanus maximus – and contained within a well-defined perimeter. We first consider round and square city models with one main street set parallel to the approaching wind and a secondary street producing an intersection at city centre. Not surprisingly, wind conditions in the two city models are dissimilar due to their shape differences. We then consider a long rectangular city model with a fully developed steady flow region along the main street. If the main street of the round city model is narrow, the parallel approaching wind cannot blow through the entire street and a penetrating inflow exists at the leeward opening. For the round city model with two crossing streets, a slightly non-parallel wind to the main street generates a stronger wind level in the entire street volume.