Papers by Elena Garcia Nevado
The link between city morphology and urban energy consumption, although proved, requires further ... more The link between city morphology and urban energy consumption, although proved, requires further research. In that sense, the analysis of parameters describing the urban texture may be a useful approach for energy assessment at a city scale. Some geometrical parameters have been used to study urban energy aspects related to the radiative phenomena, such as heat island or even a rough indicator of solar energy availability in locations where direct radiation is not determining. This paper aims to explore the correlation between one of these parameters-the Sky Factor (SF)-and direct solar radiation over facades, as a characterization tool of solar access within an urban context. Barcelona, a Mediterranean city where direct sunlight and the built environment density are deciding factors, has been chosen as case study. At different points of the facade for several urban canyons, SF value and direct solar radiation for different orientations and times of the year have been computed using Heliodon software. Both results have been related one to another and it has been found that, for a specific latitude, it is possible to define a smooth dependence between these parameters, if the orientation is taken into account. This paper shows that, beyond the SF threshold of 0.42, direct solar radiation on the facade reaches an almost asymptotic value for all orientations and times of the year.
As a result of the current economic and energy crisis, it has become necessary to rethink urban p... more As a result of the current economic and energy crisis, it has become necessary to rethink urban planning, starting from a global concept of efficiency and considering buildings not as isolated entities, but as part of an urban system, which consumes energy on a much larger scale. The connection between urban morphology and microclimate is a widely discussed question, including issues like the urban heat island phenomenon or outdoor comfort in open spaces. However, there is still a lot of work to be done regarding the influence of these microclimatic variations on building energy consumption. In that sense, would it be possible to apply efficient measures of microclimate modification on an urban scale to increase comfort levels in public spaces while at the same time, reducing building consumption? This paper focuses on urban canopy shading. Its effectiveness as a shading device and its capability to improve outdoor climate in areas with an excess of solar radiation is widely demonstrated. In this case, its effect on indoor climate of is evaluated. The case study is located in Cordoba (Spain), as an example of a climate with a hot and dry summer (according to CTE, level 4). A complete street canyon model has been created. Two buildings, one on each side of the street canyon, have been tested using an energy simulation software (Design Builder). Model features and simulation settings correspond to real values. Urban canopy shading effectiveness has been analyzed according to cooling demand decrease, taking into account both buildings. Spatial factors (street orientation, width-height ratio, windows-opaque ratio) and material factors (U-values and skin mass, % obstruction) have been considered. Results show 18% to 45% cooling demand decrease due to the canopy shading. Spatial factors are much more relevant than material factors: windows-opaque ratio is a determining factor, in contrast to mass and U-values. This study shows the importance of evaluating both urban facades, which means working from an urban perspective beyond the local scale of a single building.
Smart innovation, systems and technologies, 2023
Proceedings of the II International and IV Congress on Sustainable Construction and Eco-Efficient Solutions, 2015
As a result of the current economic and energy crisis, it has become necessary to rethink urban p... more As a result of the current economic and energy crisis, it has become necessary to rethink urban planning, starting from a global concept of efficiency and considering buildings not as isolated entities, but as part of an urban system, which consumes energy on a much larger scale. The connection between urban morphology and microclimate is a widely discussed question, including issues like the urban heat island phenomenon or outdoor comfort in open spaces. However, there is still a lot of work to be done regarding the influence of these microclimatic variations on building energy consumption. In that sense, would it be possible to apply efficient measures of microclimate modification on an urban scale to increase comfort levels in public spaces while at the same time, reducing building consumption? This paper focuses on urban canopy shading. Its effectiveness as a shading device and its capability to improve outdoor climate in areas with an excess of solar radiation is widely demonstrated. In this case, its effect on indoor climate of is evaluated. The case study is located in Cordoba (Spain), as an example of a climate with a hot and dry summer (according to CTE, level 4). A complete street canyon model has been created. Two buildings, one on each side of the street canyon, have been tested using an energy simulation software (Design Builder). Model features and simulation settings correspond to real values. Urban canopy shading effectiveness has been analyzed according to cooling demand decrease, taking into account both buildings. Spatial factors (street orientation, width-height ratio, windows-opaque ratio) and material factors (U-values and skin mass, % obstruction) have been considered. Results show 18% to 45% cooling demand decrease due to the canopy shading. Spatial factors are much more relevant than material factors: windows-opaque ratio is a determining factor, in contrast to mass and U-values. This study shows the importance of evaluating both urban facades, which means working from an urban perspective beyond the local scale of a single building.Postprint (published version
Sustainable Building for a Cleaner Environment, 2018
The work presented here has consisted in placing a thermal camera in a street of the “Petit Bayon... more The work presented here has consisted in placing a thermal camera in a street of the “Petit Bayonne,” one of the densest districts of French cities, in order to obtain a double sequence of photographs (shortwave) and thermographies (longwave) on a sunny day. The next step will be to repeat this sequence by numerical simulation to see how the measurements are used to calibrate the simulation and how the simulation can help to interpret the measurements.
Planning Post Carbon Cities: 35th PLEA Conference on Passive and Low Energy Architecture, A Coruña, 1st-3rd September 2020: Proceedings, Vol. 1, 2020 (Technical Articles), ISBN 978-84-9749-794-7, págs. 660-665, 2020
As a result of the current economic and energy crisis, it has become necessary to rethink urban p... more As a result of the current economic and energy crisis, it has become necessary to rethink urban planning, starting from a global concept of efficiency and considering buildings not as isolated entities, but as part of an urban system, which consumes energy on a much larger scale. The connection between urban morphology and microclimate is a widely discussed question, including issues like the urban heat island phenomenon or outdoor comfort in open spaces. However, there is still a lot of work to be done regarding the influence of these microclimatic variations on building energy consumption. In that sense, would it be possible to apply efficient measures of microclimate modification on an urban scale to increase comfort levels in public spaces while at the same time, reducing building consumption? This paper focuses on urban canopy shading. Its effectiveness as a shading device and its capability to improve outdoor climate in areas with an excess of solar radiation is widely demonst...
The link between city morphology and urban energy consumption, although proved, requires further ... more The link between city morphology and urban energy consumption, although proved, requires further research. In that sense, the analysis of parameters describing the urban texture may be a useful approach for energy assessment at a city scale. Some geometrical parameters have been used to study urban energy aspects related to the radiative phenomena, such as heat island or even a rough indicator of solar energy availability in locations where direct radiation is not determining. This paper aims to explore the correlation between one of these parameters -the Sky Factor (SF)- and direct solar radiation over facades, as a characterization tool of solar access within an urban context. Barcelona, a Mediterranean city where direct sunlight and the built environment density are deciding factors, has been chosen as case study. At different points of the facade for several urban canyons, SF value and direct solar radiation for different orientations and times of the year have been computed usi...
Facade design has significant effects on inner conditions of spaces and also on the energy needs ... more Facade design has significant effects on inner conditions of spaces and also on the energy needs to achieve user’s comfort. In this regard, the proportion of glazed surfaces to opaque ones plays a key role. Although the link between the fenestration ratio and energy demand for a space has been widely addressed in literature, a considerable number of these studies were based on isolated models, disregarding the effect of the urban surroundings. The aim of this paper is to provide insights on the impact of the window-to-wall ratio (WWR) on thermal energy demands taking into consideration a specific urban context. The Eixample district of Barcelona, with Mediterranean temperate climate, has been selected as the case study. Heating and cooling energy needs have been evaluated for a single residential space by means of computer simulations in Design Builder for different positions within the tissue. Results show that, from a thermal point of view, the design of facade openings within an ...
Sustainable Vernacular Architecture, 2019
Around 2030, world cities will have six billion inhabitants, whereas they had just a few tens of ... more Around 2030, world cities will have six billion inhabitants, whereas they had just a few tens of millions only two centuries ago. This very rapid urbanization is the most striking feature of our history since the beginning of the industrial era, and our ability to better plan cities has become a major issue for the survival and development of our civilization. Since the founding of the first cities, 5000 years ago, physical parameters such as sunshine and prevailing winds have been taken into account, but only in a very simplified way, essentially geometric. The slow maturation of urban physics, capable of quantifying and interpreting physical phenomena and their interaction with urban shapes, has been largely dependent on the progress made in the three-dimensional representation of the city and its flows. In this chapter, we recall the three determining steps of urban planning: the Urban Revolution, the Perspective Revolution, and the Industrial Revolution. The development of the perspective vision in the second and the heat theory in the third one serves as references to develop a key representation of urban physics: the infrared perspective. The difficulties of its realization by the measurement are then described, before inducing the next step, its realization through simulation.
Sustainable Cities and Society, 2020
The overheating of the street surfaces has negative impacts on pedestrian comfort and cooling ene... more The overheating of the street surfaces has negative impacts on pedestrian comfort and cooling energy consumption. During the past few decades, extensive research has been carried out on heat mitigation technologies. However, there is limited knowledge on the efficacy of textile solar protections at the urban scale. In this paper, we investigate the cooling potential of sun sails on urban surfaces based on field measurements carried out in several streets of Cordoba (Spain). To this end, we develop a novel method based on time-lapse thermography at street level that allows for assessing the thermal behavior of urban scenes, in a comprehensive and agile way. Results show that high-mounted sun sails have a global cooling effect over the street, regardless of its orientation. Decreases due to sun sails in ground temperature reach up to 16°C, and in façade temperature, up to 6°C. Our observations demonstrate that sun sails can provide a heat mitigation efficacy similar to standard technologies while entailing softer levels of intervention.
Computer Graphics Forum, 2020
Urban thermography is a non-invasive measurement technique commonly used for building diagnosis a... more Urban thermography is a non-invasive measurement technique commonly used for building diagnosis and energy efficiency evaluation. The physical interpretation of thermal images is a challenging task because they do not necessarily depict the real temperature of the surfaces, but one estimated from the measured incoming radiation. In this sense, the computational rendering of a thermal image can be useful to understand the results captured in a measurement campaign. The computer graphics community has proposed techniques for light rendering that are used for its thermal counterpart. In this work, a physically based simulation methodology based on a combination of the finite element method (FEM) and ray tracing is presented. The proposed methods were tested using a highly detailed urban geometry. Directional emissivity models, glossy reflectivity functions and importance sampling were used to render thermal images. The simulation results were compared with a set of measured thermograms, showing good agreement between them.
Building and Environment, 2021
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Building and Environment, 2018
Thermograms of urban perspective views provide an efficient way to analyze heat transfer phenomen... more Thermograms of urban perspective views provide an efficient way to analyze heat transfer phenomena in cities. The computational simulation of thermograms introduces more information into the analysis, allowing for the comparison of spatialized information to provide a better understanding of the involved physical parameters. The main objective of this work was to simulate thermograms at the urban scale using the finite element method (FEM). Geometrical properties and environmental and boundary conditions were carefully established. A comparison between a time sequence of thermograms on a real urban district and a set of simulated thermograms was developed. The computational model shows compelling results, reproducing the same order of magnitude and general appearance of the experimental data. Moreover, the results allow for the evaluation of the heat flux balance at various interesting points on the geometry, and the impact associated with the modification of scene parameters.
Energy Procedia, 2017
District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.
Energies, 2016
The urban canyon model has been recurrently used as a basis for many solar access studies. Howeve... more The urban canyon model has been recurrently used as a basis for many solar access studies. However, its conception as endless structures disregards the effect of street intersections, despite being characteristic elements of urban fabrics. This paper aims to evaluate the impact of street discontinuities on solar access over building façades. The potential of crossings to increase the available radiation has been assessed through computer simulations in dense urban environments in a Mediterranean location. For the cases studied, results show that local effects of an intersection almost disappear beyond a specific distance for each aspect ratio, which can be helpful to determine the suitable level of detail for solar analyses at an urban fabric scale.
Journal of Physics: Conference Series, 2019
The correlation between air and surface temperatures is recurrently used as a descriptor of the u... more The correlation between air and surface temperatures is recurrently used as a descriptor of the urban climate within built environments. The aim of this paper is to explore the possibilities of time-lapse thermography to visualize this relationship in time and space. To this end, thermograms are colorized using a relative-to-air temperature scale, instead of the usual absolute one. This approach was tested for two deep urban canyons belonging to cities with different climates. Relative-to-air thermography has two main advantages: it facilitates comparisons between the thermal responses of urban scenes under different climates and makes convective energy exchanges more comprehensive.
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Papers by Elena Garcia Nevado