Urban Microclimate Modelling for Comfort and Energy Studies

Urban metabolism is a new field of study, which converges topics from many disciplines, like architecture and planning, urban climatology, urban physics, environmental psychology, sociology, anthropology and engineering. In this chapter the city is studied as a thermodynamic system, focusing on the properties of adaptive, complex open systems to describe the behaviour of such a structure. The general theory of complex systems is presented, and then some hypotheses are formulated to explain the evolutionary process that happens in a city as the result of two big principles operating on the system: one increasing efficiency, and the other increasing diversity. The link between thermodynamics and information theory is explored through the concept of entropy, while the city is interpreted as a negative entropy processor. Urban climate is discussed and interpreted under the same principles. Resilience-oriented urban planning is finally proposed as a need to reconstruct a more dialectical dialogue with nature.

The urban heat island phenomenon (UHI) is a ubiquitous feature of cities and describes the fact that cities are generally warmer than the natural areas that surround them. The UHI has been a subject of study for 200 years but it is only in the last 50 years that the causal processes have been measured and modelled. The UHI itself encompasses four distinctive types: the canopy-layer UHI which forms in the airspaces between buildings; the surface UHI which forms on the interface separating the solid (ground, walls, roof, etc.) from the adjacent air; the boundary-layer UHI which forms at height over the rooftops of buildings and maybe 1–2 km deep; and the substrate UHI formed below ground level. Each of these outcomes can be understood within the framework of the energy budget, which can be applied to a volume and describes the types of energy, their net flux and the temperature response. This chapter discusses the formation of the UHI using an energy budget framework to understand these processes and their outcomes at different time and space scales. It outlines a brief history of the UHI, the energy budget underpinnings and the methods employed. This perspective is used to place climate actions that seek to adapt and mitigate the UHI phenomenon in a physical context.

This chapter addresses urban comfort beyond thermal physiology. Demonstrating the influence of microclimatic and thermal comfort conditions, an inherent characteristic of the space, on use and activities in urban areas, the work aims to provide a more comprehensive framework for urban designers and planners. Looking at field surveys across the world, it focuses on understanding outdoor thermal comfort and how our adaptive capacity is enhanced through a range of adaptive mechanisms, from conscious actions to a range of parameters in the contextual framework of psychological adaptation, temporality and cultural norms. The work highlights the need for adaptive capacity and thermal resilience at the individual level, as well as spatial scale, supporting environmental diversity. In a warming climate and amidst a global health pandemic, outdoor comfort becomes an important commodity, where the design of open spaces has the potential to play a critical role not only in climate regulation and energy, but also in health, liveability and social cohesion.

This chapter presents the urban microclimate impact on comfort and energy demand by buildings located in high-latitude temperate regions, characterised by higher heating demand compared to cooling. It focusses on London as a case study of such a location and presents results from measurements and computational studies during the last 20 years. The relationship of surface and air UHI in high-latitude cities is first described as well as the relationship between UHI and building energy demand; results from London are used to illustrate the impact. It follows a description of urban albedo outlining contributing parameters. Modelling tools enabling the study of microclimate impact on indoor thermal conditions are then described. Recent results of a study of urban albedo in London and the application of modelling tools are presented.

Cities in the Mediterranean basin are characterised by compact and dense urban fabric, leading to a strong night-time urban heat island (UHI) intensity which increases thermal discomfort and building energy use in summer. This chapter reviews several experimental and numerical studies investigating the UHI intensity in representative Mediterranean cities, discussing the limitations and suitability of different approaches based on the purpose of the analysis (i.e. outdoor thermal comfort or building energy efficiency). Some recurrent urban climate characteristics are highlighted, such as the importance of urban morphology and sea breeze, the range of the daytime and night-time UHI intensity and its seasonal variability. Case studies of Rome and Barcelona are used to present modelling approaches to integrate urban climate in building energy performance. The complexity of the urban climate modifications in this context and their net energy impact on buildings are discussed considering UHI intensity, mutual shading between buildings, urban surface temperatures and wind speed in urban canyons. The last section is dedicated to urban and building design strategies for heat management in Mediterranean cities, including effective UHI mitigation measures and flexible passive cooling design strategies for buildings.

A lack of scientific basis for the conception and development of urban environments has been evidenced in tropical climates. The lack of urban morphology and climate data needed for carrying out the analyses has been a major barrier for researching into context-specific urban and building elements, including building energy systems, for achieving adequate indoor environmental conditions at low energy consumption. The result has been air-conditioned buildings with poor energy performance, unconditioned spaces unsuitable for human comfort and an increasing trend for installation of active cooling systems in offices and homes, all expected to escalate with climate change. Therefore, there is pressing need to come up with scientific findings to address the urban climate issues in tropical countries. This chapter presents the main research findings reported in literature related to (a) understanding the factors influencing energy performance and thermal comfort in tropical climates, and (b) practical realisation of measures in the built environment, with reported outcomes. These findings are used to devise a road map for bettering energy performance and comfort in buildings in tropical contexts while identifying research gaps.

It is a well-known fact that different design characteristics applied to urban spaces, such as streets, public squares and parking lots can generate completely different microclimatic thermal conditions. In this chapter, a comparison among different outdoor urban spaces in an arid climate is presented, in which the effect of vegetation on microclimatic conditions and thermal comfort is highlighted. Surface temperature measurements, as well as climatic parameters within the space limits are described and studied to show the vegetation’s thermal effect on microclimatic conditions in outdoor spaces. The effects of different characteristics of the outdoor spaces on microclimatic variables are discussed.Finally, microclimatic conditions of outdoor spaces around low-cost dwellings in a desert city are analyzed: entrance, backyard, and outdoor laundry spaces. Design characteristics and common improvements in these spaces are described, such as the use of different shadow devices and the change in pavement materials. The impact of thermal design features in these spaces on the energy consumption of buildings is also shown.

Cities are a spatial nexus for the anthropogenic drivers of climate changes at local, regional and global scales. These drivers are the result of countless decisions made at a hierarchy of urban scales (building, neighbourhood and city) that have accumulated over time. Cities are also places that are exposed to natural and enhanced hazards and are at particular risk owing to the concentration of population and infrastructure, much of which is vulnerable. For all of these reasons, cities are a focus of climate management strategies that includes air quality, indoor thermal comfort, mitigation and adaptation, etc. Each of these strategies are often the purview of specialist fields that have a narrow focus on specific issues. However, effective management of the urban climate will require an integrated knowledge base to support decision-making. This chapter outlines the need for this integration and identifies the link between indoor and outdoor climates as a critical gap in urban climate management.

One of the consequences of the dramatic increase in urbanization that has taken place in recent years is the replacement of rural and green areas with roads, vast extents of concrete and large vertical surfaces. The air circulation in urban areas is different from that in the surrounding rural environment and is difficult to predict because it largely depends on the arrangement of buildings and streets, presence of vegetation and other topographic features. In order to improve our understanding of wind field in cities, field measurements, laboratory-scale physical modelling and numerical simulations have been widely used during the last decades. We address this subject providing a summary of the present knowledge of air circulation in urban areas, focusing on the case of neutral atmosphere. The most common flow topologies encountered in urban canopies are described, which include archetypal simplified geometrical configurations such as the isolated building, street canyons, groups of buildings and street intersections.

Understanding the urban heat island (UHI) phenomenon aids in the better predictions and analyses of its mitigation strategies. The mesoscale Weather Research and Forecasting Model (WRF) tool has been increasingly proposed to assess the UHI and to perform microclimate analysis. In this tool, mesoscale models are coupled separately with urban canopy models (UCMs) to predict the heat emission and moisture fluxes from the urban boundaries to the atmosphere. The three commonly considered UCMs to represent the canopy are slab (SB), single layer (SL), and multilayer (ML). These models account for the buildings in terms of roughness elements, two-dimensional structures, and three-dimensional urban surfaces, respectively. In this chapter, the WRF-UCM interaction is explained, and the capabilities and shortcomings of each UCM are described. The WRF-UCMs are used to assess two specific heat wave periods in the case study of the Greater Toronto Area (GTA) in Canada. To evaluate the WRF-UCM, the simulated variables are compared against the measured data obtained, showing the strong value of these new approaches. The UHI intensity (UHII) is further evaluated by the differences in ambient temperature in urban and rural areas during two heat waves, in July 2011 and 2018. The results illustrate that the daily UHI intensity is around 1.2–1.5 °C, while in the daytime it is near 0.7 °C. This chapter, based on the analysis of the selected case study, shows that the SL-UCM is reliable for climate simulations. Finally, to precisely evaluate the UHI intensity and to analyze more sophisticated canopies within cities, the ML-UCM needs to be applied to consider fully both the turbulent kinetic energy and the radiation reflections in the urban canopy.

Deciphering the urban microclimate is a long-standing research topic which has been lately consolidated as a major interest in the built energy and environment community. Research investigates at a fast pace the physical laws and simulation techniques to better understand the urban built environment and the ways of improving it. The snap increase in the amount and breadth has come at a price of little systematization and appreciation of knowledge. With that in mind, this chapter provides a gentle overview of the Urban Weather Generator (UWG), a physics-based microclimate simulation paradigm developed and maintained over the past decade to quantify the energy interactions between buildings and urban climate. This chapter favours a consistent and progressive introduction of the main concepts and architectural treatments in the UWG over an exposition of the most related literature. Knowledge of changes in the urban environment and their effect on building energy performances can potentially support a better decision-making framework for civil engineering systems, particularly at the planning and design stage. We present the initial motivations, theoretical models, case studies, and practical achievements of the UWG that have thus far been made as well as the many challenges that await us in this nascent field. This chapter aims to give an insight into the importance of considering the urban microclimate as well as to stimulate further research.

The SOLENE-microclimat model has been developed to investigate the consequences of urban context on local microclimate and indoor thermal conditions. It is dedicated to modeling urban microclimate and building thermal behavior at the district scale. The modeling approach is based on the coupling of several modules: radiative, thermal, and CFD models. The model can simulate a large range of cases encountered in urban projects: modeling of vegetation, water ponds, soils, building energy simulation, and techniques such as cool paints and surface water aspersion. It offers a way for enhancing the knowledge and constitutes a decision-making support system for establishing effective urban environmental policies. For each module included in SOLENE-microclimat, the validation steps that have been carried out to check the model’s ability to accurately represent phenomena are presented. Two case studies are presented to show how this tool has been used to assess and compare climate adaptation measures based on vegetation (trees, lawns, green walls, and roofs), water use (aspersion), and cool materials. The advantage of SOLENE-microclimat is its ability to model all the fluxes at both the building and the district scales. This helps in understanding the direct and indirect effects of various adaptation measures and their relative impact on building energy demand and indoor/outdoor thermal comfort.

Due to digital advancements, climate and energy modellers can take advantage of increasingly sophisticated codes to shed new light on the complex urban dynamics. Nonetheless, the range of model solutions practitioners can address is broad and choosing the proper device could be hard. Thus, we compare two modelling strategies on the same local-scale domain to assess thermal stress and urban heat island effects, using two popular numerical codes: ENVI-met and Grasshopper. The analysis highlights limits and potential of these modelling choices, comparing technical aspects as user interface, customisability, input parameters, computational effort, scalability, discretisation and algorithms. ENVI-met results to be more suitable for microscale domains, able to reproduce multiple variable interactions ensuring high-detailed solutions. Software shows limitations to be scaled towards urban-scale domains due to high computational effort. ENVI-met is an all-in-one software and interconnection with external tools is little explored. Integration with domain field data is essential for calibration. Grasshopper is a scalable modular engine, based on visual programming and open-source plug-ins. It results to be more appropriate to local scale, displaying less detailed solutions but guaranteeing larger spatial domains. Plug-in interconnection makes user interface demanding, although a programming background is dispensable. Integration with field data is unnecessary but useful for validating results.

This chapter presents a review bringing a critical overview of the different ways in which the urban microclimate is currently considered in building design simulations. Therefore, different building energy models (BEMs) and urban climate models (UCMs) are presented. The ways these tools communicate are presented and the impact of UHI and the microclimate is assessed. For example, when conducting simulations neglecting the UHI, the variations can range from 10% to 200% for cooling demand and from 3% to 89% for heating demand with respect to simulations considering the UHI. Microclimate boundary conditions show to reduce loads by 130% for heating and 25% for cooling. The remaining scientific obstacles for better consideration of the urban climate context affecting the BEMs are discussed in this chapter. Some findings are the following: in some papers the boundary conditions of the BEM are only partially corrected; the BEM does not systematically introduce a feedback to the UCM; the simulation for a coupling project is usually launched for some days but longer simulation periods are necessary for an appropriate design of bioclimatic buildings. This could be done with parametric UCM tools. Future work should be about how to validate with experimental measurements the co-simulation results obtained.

Urban climate modelling and simulations are crucial in the field of human biometeorology in order to assess human thermal comfort within urban environments. The microscale models RayMan and SkyHelios are presented and applied for a study area to show the possibilities and advantages of three-dimensional vector-based modelling for human thermal comfort analysis. The principles of human biometeorology for thermal comfort assessment: mean radiant temperature (T_mrt), physiologically equivalent temperature (PET), and other thermal indices are presented. These parameters are further analyzed to show the spatial effects of shading and wind speed on T_mrt and PET by urban obstacles (e.g., buildings) and vegetation. In addition to that, results with high temporal resolution of several factors and parameters are shown for a location of interest within the study area. Results show that the RayMan model can be best applied for the analysis of thermal comfort at specific points within a model domain, but for long meteorological datasets. The SkyHelios model on the contrary is most suitable for spatial analysis of thermal comfort for large areas like urban districts and in high spatial resolution of, e.g., 1 m.

Global average surface-air temperatures over land and oceans have been increasing over the past 100 years mainly because of anthropogenic climate change. Cities, due to the concentration of population, economic activities, and built infrastructures, are high-risk and potential damage areas in global warming scenarios. Specific microclimate conditions, which occur in urban areas, are expected to change with almost certainly disadvantageous effects on the energy consumption of buildings and the quality of life at outdoor spaces. Most buildings have a life span of several decades, during which the urban microclimate will continue to change gradually. Building energy simulation (BES) programs are capable of predicting building energy performance in detail in a dynamic model. These models should ensure that new buildings will adapt to future conditions. Nevertheless, the meteorological data used as input, even if it is in situ-measured urban microclimatic data, are generally based on current or past weather conditions and do not attend future scenarios. The objective of this chapter is to present a parameterization of the impact of urban microclimatic conditions on energy performance of buildings in the current situation (2020), and in three tentative future scenarios assuming the microclimatic conditions from RCP 4.5 (2015–2039) and RCP 8.5 in two time lapses (2015–2039 and 2075–2099) from the fifth IPCC report. As application example, a case study in the city of Mendoza, Argentina, is presented. First, the model is run in the BES program EnergyPlus with the current urban microclimatic conditions, calibrated with on-site measured data. Then, the same model is run for microclimatic RCP scenarios. Meteorological conditions are adopted from a predictive mathematical model of the IPCC using EPW files as input. Based on the obtained results, the impact of climate change on urban microclimate and expected changes in energy consumption of buildings during the next century are discussed.

The spatial configuration of cities has recently been the subject of several studies in a variety of disciplines, including geography, urban ecology, urban design, and urban and building physics. As a reaction to the demanding need to reduce the environmental impact of cities, research efforts have focused on the unintended interaction between urban form, microclimate and energy both with diagnostic and design perspectives. The above-mentioned interaction has required the introduction of several metrics able to measure and characterize urban form at a different scale (built form, density, typology, settings, etc.) and to act as performance indicators in microclimate and energy studies. The proposed section puts the issue in an interdisciplinary perspective, addressing the ability of spatial metrics to predict local climate, thermal comfort and energy demand. Basic knowledge of urban morphology and a systematic review of most common metrics are presented and discussed. Then a framework for understanding the capability of existing research methods for microclimate and energy performance assessment is proposed. Finally, critical evaluation on the relevance and roles of urban metrics for supporting urban analysis and fostering climate-responsive design is developed in order to highlight current limitations and offer suggestions for further progress in the field.

Extreme temperatures mirror global climate patterns. The physical characteristics of the landscapes of cities and the activities of their citizens have decisive consequences on urban climates. Both are indeed manageable through urban planning, and especially with the potential of greening urban landscapes. This chapter analyses the capacity of urban green infrastructure (GI) to mitigate extreme temperature. Greening urban landscapes means not only increasing the proportion of planted land in cities, but also acknowledging the distinct contributions of different elements of GI on urban conditions, particularly climate. Based on a literature review, this chapter delves into the mechanisms for the scaling effects of mitigating urban heat islands (UHI) by GI. UHI are urban centres with significantly higher temperatures than those of surrounding rural areas. Within cities, UHI varies in shape and intensity, with lower temperatures in the presence of some GI elements. A deeper understanding of the distinct and synergetic contributions of GI components and the mechanisms involved is needed to green urban climates and manage the multiscale and nested nature of GI.

Cities have a synergy between the microclimatic conditions generated by the urban form, their interaction with its envelope materials and trees, and building energy consumption. From an energetic and environmental perspective, planning and designing neighborhoods that help to reduce the temperature of outdoor air are necessary to improve cities’ efficiency. This chapter collects and discusses the research works carried out by the Institute of Environment, Habitat and Energy, part of the National Scientific and Technical Research Council (CONICET) in Mendoza, Argentina. This work aims to assess the impact of the urban canyon structure and urban grid forms on thermal behavior and energy consumption in “oasis cities” of arid regions.

When considering existing approaches to urban contexts and their responsiveness to encircling climatic conditions, the international scientific community has identified a weakness in applicative know-how to approaching local thermal comfort conditions. As a result and particularly associated to bottom-up approaches to climate adaptation, local decision-making and design are frequently met by a lack of instruments and means to (1) address concrete local outdoor thermo-physiological thresholds and (2) render such biometeorological risk factors into opportunities for thermal sensitive local urban design and architectural practices. Recognised as a city that requires urgent action in adapting to existing and future climatic conditions that are already being witnessed within its urban environment, this chapter shall focus upon the case of Lisbon. Within this setting, the imperative interdisciplinary application of biometeorological models on behalf of local agents such as architects and urban designers is discussed. Based upon a ‘best practice’ perspective to approaching local adaption and mitigation of climatic risk factors associated to Mediterranean climates, the objective of the chapter is to assess the overall potential of models such as RayMan and SkyHelios to (1) carry out vital local assessments based upon easily accessible climatic and morphological data and (2) render more accurate outputs that better inform how existing and future climatic risk factors can be approached through thermal sensitive architectural and urban design practices.

Building thermal performance and its energy consumption are affected by the energy exchange processes taking place between the outer skin or envelope of the building and the surrounding environment. It is a dynamic system in which there are continuous changes in a daily and seasonal range. Quantity and quality of the exposed envelope as well as albedo, vegetation, and urban geometry are significant factors in determining the impact of urban microclimates on energy building consumption. Existing buildings and their microclimates can be monitored in situ. This practice is very useful but time and resource consuming. Only some punctual cases can be evaluated thoroughly, and it is impossible to measure buildings that are still in project. Building energy simulation (BES) programs are capable of modelling building energy performance in detail in a dynamic model. The weather variables in an urban microclimate may be subtly different from the conditions prevailing over the area as a whole. Nevertheless, the input of meteorological conditions is usually taken from long-term averages provided by local weather stations. These data series ignore the modifying effect on the surroundings. This chapter presents a case study in a high-density area in the city of Mendoza, Argentina, in which year-round in situ measurements of temperature, humidity, radiation, and air movement were taken in two different scales: within the streets in a neighborhood and outside and inside a building. The micro-urban scale and the building scale were covered. A specific weather file was created for each scale, to be integrated in simulation software ENVI-met and EnergyPlus, respectively. Models were calibrated with the monitored data, to be run again with the information provided by local weather stations. Also, as a third term of comparison, the simulation workflow moves from the micro-urban- to a building-scale assessment by linking the ENVI-met software microclimatic results to the building energy simulation program EnergyPlus. Results obtained (a) with the local weather stations average climate input, (b) with the on-site microclimatic measurements, and (c) with ENVI-met software are compared in order to assess each case reliability in assessing the impact of local urban climate on building energy performance. Simulated-monitored results present differences of ±3.5%. This study reveals the capabilities and advantages of working with this tool for the generation of microclimatic data, which when integrated with EnergyPlus presents a less expensive and fast alternative to in situ monitoring.

Over the past decades, intense urbanisation processes resulted in built environments with a severe lack of green spaces and thus with low potential for mitigating the heat stress. Green spaces are the main providers of ecosystem services in cities and play a relevant role, among others, in regulating the local microclimate and in mitigating the urban heat island effect. However, despite their importance, the implementation of green infrastructure still struggles and is challenged by the lack of available open spaces to be set as new urban green areas.

This chapter addresses the potential effectiveness of trees in reducing the energy demand for cooling and heating in buildings located in urban areas. In particular, the research considers different types of spatial configuration of urban fabrics and urban green, and discusses the expected impact of a series of parameters such as the relative position of trees and buildings, the species of trees to be planted, and the availability of space for new tree planting.

The discussion is based on the results available in the literature, and shows that a sound urban planning strategy aimed at designing an effective green infrastructure can significantly reduce the energy demand of urban fabric while providing new green spaces, implementing climate change adaptation strategies, and creating a more safe and energy-efficient environment.

Cool materials are an acknowledged, environmentally friendly and relatively cost-effective solution that can be easily integrated in the built environment with the threefold aim of reducing building cooling energy needs, mitigating the urban heat island (UHI) phenomenon and, at a larger scale, counteracting global warming. High solar reflectance and infrared thermal emittance are the main properties to be aimed at when developing a cool material. As a matter of fact, by reducing the amount of energy absorbed by a surface and contemporarily improving its capacity to dissipate heat it is possible to reduce surface overheating and improve urban microclimatic conditions by decreasing air and surface temperatures both indoors and outdoors. This chapter presents the main characteristics of cool materials, together with their most common characterization procedures and techniques, with a specific focus on the most innovative solutions available in the present research panorama. The most recent advances and developments in cool materials engineering are addressed and an innovative classification is presented, trying to highlight avant-garde solutions that are currently being developed for improving building energy efficiency.