UWG -TRNSYS Simulation Coupling for Urban Building Energy Modelling

This paper presents a new methodology to carry out building performance simulation at the district scale integrating the building thermal model TRNSYS with the climate model ‘Urban Weather Generator’ (UWG). The integrated methodology is designed to include the microclimatic modifications induced by urban environments on buildings’ cooling load calculation. The impact of shadows, air temperature increase and urban radiant environment on building cooling performance has been highlighted for hot arid climates (Antofagasta, Chile). Results indicate that the impact of urban context on energy performance of buildings at the neighbourhood scale varies significantly with building typology and urban tissue densit

Publishing a data paper to share weather datasets

Objectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats Sostenible

Resilient cooling of buildings: state of the art review

Name of the research project : IEA Annex 80 – Resilient Cooling of Buildings Publisher: Institute of Building Research & Innovation ZT GmbH, AustriaThis report summarizes an assessment of current State-of-the Art resilient cooling strategies and technologies. It is a result of a collaborative work conducted by participants members of IEA EBC Annex 80. This report consists of four chapters. In the first chapter are included relevant technologies and strategies that contribute to reducing heat loads to people and indoor environments. These technologies/strategies include Advanced window/glazing and shading technologies, Cool envelope materials, Evaporative Envelope Surfaces, Ventilated Envelope Surfaces and Heat Storage and Release. In the second chapter are assessed cooling strategies and technologies that are responsible for removing sensible heat in indoor environments: Ventilative cooling, Evaporative Cooling, Compression refrigeration, Desiccant cooling system, Ground source cooling, Night sky radiative cooling and High-temperature cooling systems. In the third chapter various typologies of cooling strategies and technologies are assessed inside the framework of enhancing personal comfort apart from space cooling. This group of strategies/technologies comprise of: Vertical-axis ceiling fans and horizontal-axis wall fans (such fixed fans differ from pure PCS in that they may be operated under imposed central control or under group or individual control), Small desktop-scale fans or stand fans, Furnitureintegrated fan jets, Devices combining fans with misting/evaporative cooling, Cooled chairs, with convective/conductive cooled heat absorbing surfaces, Cooled desktop surfaces, Workstation micro-air-conditioning units, some including phase change material storage, Radiantly cooled panels (these are currently less for PCS than for room heat load extraction), Conductive wearables, Fan-ventilated clothing ensembles, Variable clothing insulation: flexible dress codes and variable porosity fabrics. In the fourth chapter technologies and strategies pertinent to removing latent heat from indoor environments are assessed. This group includes Desiccant dehumidification, Refrigeration dehumidification, Ventilation dehumidification, and Thermos-electric dehumidification.Preprin

Mitigation strategies of the urban heat island intensity in Mediterranean climates: simulation studies in Rome (Italy) and Valparaiso (Chile)

The Urbanocene, a proposed new geological epoch characterized by the urban living condition, is pressing the humanity to respond shortly to important challenges. Cities are at the same time the places where we live in and the big dissipators of the final energy to the environment. The simultaneous rules of heat dissipator and place to live are quite contradictory, because of the increasing temperatures of the dissipator surfaces, phenomenon known as Urban Heat Island (UHI). Mediterranean climates should suffer, in the next years, changes in the thermal needs of buildings and in the outdoor comfort sensations. A change in the energy demand from heating to cooling is probable and overheating reduction could be a priority in the future. Many mitigation strategies of UHI are being discussed in these years, such as the city greening, the use of cool materials for roofs and soils, the reduction of automobile dependence, the shift to new urban morphologies. In this paper an evaluation of impacts of different possible strategies is done, by using computational simulations for various sectors of Rome and Valparaiso. Results show the importance of greening and traffic reduction to achieve better comfort; while to reduce building energy consumption changes in urban morphology and traffic are suggested as the best strategies

Which climate for each urban context? A preliminary comparative study on urban climate prediction and measurement in different districts in Rome and Barcelona

The research progress in building energy modeling and simulation has led to the widespread diffusion of more and more sophisticated software. By contrast, there aren't such effective results when it comes to the urban-scale climate modeling, whose geometric, morphological, material and anthropogenic features clearly distinguishes it from a rural context. The clearest effect of these differences is the Heat Island phenomenon. Despite that, the weather files currently used for energy simulations practice refer to measurements gauged in out-of-town weather stations, as like airports, causing the results to be unreliable and inaccurate. The aim of this study is to prove that, despite referring to the same region, latitude or city, quite different microclimates may occur depending on urban local features. To this purpose, temperature data available in urban weather stations located in Rome and Barcelona are inspected and compared to the rural reference station, in order to evaluate the difference of Heat Island intensity in different urban context. The experimental verification is then used to evaluate a recently developed method for generating urban weather files from a rural station, the Urban Weather Generator (UWG). The experimental verification shows a maximum intensity of Urban heat island in Barcelona in July, with a Dt of 4.7° C at 18:00 local time. In the case of Rome there is a maximum Dt of 5° C in August at 17:00 local time. The comparison between measured data and calculate data show that the reliability of the UWG calculation strongly depends on the location of the urban site within the city and on its features. The temperature discrepancies decrease when the urban site is located in a fairly central position and in a rather homogeneous urban fabric. There is a systematic error during the central hours of the day which suggests an underestimation of the effect of radiation and radiative trapping

Predicció urbana de l’illa de calor en el context mediterrani: una avaluació del model generador de temps urbà

The lack of urban-specific climate data is, today, one of the major limits for an accurate estimation of the building energy performance in the urban context. The urban climate is substantially modified by the “heat island” effect that determines an increase of the air temperature compared to the surrounding rural areas. By contrast, the weather data used to run the energy simulations normally refer to rural or suburban weather stations, causing relevant errors in the energy assessment, especially in hot climates.This study aims at evaluating the accuracy of the "Urban Weather Generator" (UWG), a model developed for generating urban weather files from rural weather data in order to improve the accuracy of the building energy simulations in the urban context.To this purpose, the model predictions have been compared to actual observations in different urban sites in Rome and Barcelona. The comparisons have been conducted for one year of observations for each site, focusing the analysis on summer and winter months. The model accuracy has been assessed through statistical analysis of the average error.Results show that the UWG model is able to capture the general trend of the urban temperature. The accuracy of the prediction increases for urban sites located in a rather homogeneous urban fabric in terms of building density and vegetation coverage. In these situations, the model allows a good prediction of the urban air temperatures with low computational requirement and it can be a useful tool to improve the accuracy of urban energy analysis.La falta de datos climáticos urbanos específicos es, hoy en día, uno de los principales límites para una estimación precisa del desempeño energético de los edificios en el contexto urbano. El clima urbano es sustancialmente modificado por el efecto "isla de calor" que determina un aumento de la temperatura del aire en comparación con las áreas rurales circundantes. Por el contrario, los datos meteorológicos usados para ejecutar las simulaciones de energía normalmente se refieren a estaciones meteorológicas rurales o suburbanas, causando errores relevantes en la evaluación energética, especialmente en climas cálidos. Este estudio tiene como objetivo evaluar la exactitud del "Generador de Tiempo Urbano" (UWG), un modelo desarrollado para generar archivos meteorológicos urbanos a partir de datos meteorológicos rurales con el fin de mejorar la precisión de las simulaciones energéticas de los edificios en el contexto urbano. Con este propósito, las predicciones del modelo se han comparado con observaciones reales en diferentes lugares urbanos de Roma y Barcelona. Las comparaciones se han realizado durante un año de observaciones para cada sitio, enfocando el análisis en los meses de verano e invierno. La precisión del modelo se ha evaluado mediante el análisis estadístico del error medio. Los resultados muestran que el modelo UWG es capaz de capturar la tendencia general de la temperatura urbana. La exactitud de la predicción aumenta para los sitios urbanos situados en un tejido urbano bastante homogéneo en términos de densidad de edificios y cobertura de vegetación. En estas situaciones, el modelo permite una buena predicción de las temperaturas del aire urbano con un bajo requerimiento computacional y puede ser una herramienta útil para mejorar la precisión del análisis de energía urbana.La manca de dades climàtiques urbans específics és, avui, un dels principals límits per a una estimació precisa de l'acompliment energètic dels edificis en el context urbà. El clima urbà és substancialment modificat per l'efecte "illa de calor" que determina un augment de la temperatura de l'aire en comparació amb les àrees rurals circumdants. Per contra, les dades meteorològiques que es fan servir per a executar les simulacions d'energia normalment es refereixen a estacions meteorològiques rurals o suburbanes, causant errors rellevants en l'avaluació energètica, especialment en climes càlids. Aquest estudi té com a objectiu avaluar l'exactitud del "Generador de Temps Urbà" (UWG), un model desenvolupat per generar arxius meteorològics urbans a partir de dades meteorològiques rurals per tal de millorar la precisió de les simulacions energètiques dels edificis en el context urbà. Amb aquest propòsit, les prediccions del model s'han comparat amb observacions reals en diferents llocs urbans de Roma i Barcelona. Les comparacions s'han realitzat durant un any d'observacions per a cada lloc, enfocant l'anàlisi en els mesos d'estiu i hivern. La precisió del model s'ha avaluat mitjançant l'anàlisi estadística de l'error mitjà. Els resultats mostren que el model UWG és capaç de capturar la tendència general de la temperatura urbana. L'exactitud de la predicció augmenta per als llocs urbans situats en un teixit urbà bastant homogeni en termes de densitat d'edificis i cobertura de vegetació. En aquestes situacions, el model permet una bona predicció de les temperatures de l'aire urbà amb un baix requeriment computacional i pot ser una eina útil per millorar la precisió de l'anàlisi d'energia urbana.Peer Reviewe

Urban morphology and energy performance: the direct and indirect contribution in mediterranean climate

The combined effects of urban heat island (UHI), urban population growth and energy overexploitation are undermining the safety of urban areas. Urban morphology plays a prominent role in this context, because it affects building's energy demand and local climate at urban scale. However, this contribution is recurrently neglected. The present contribution seeks to investigate the direct and indirect effect of urban morphology on buildings energy performance in the Mediterranean climate. Urban morphology affects energy demand by modifying two relevant variables: outdoor air temperatures and incident radiation. The relevance of these effects were studied on a sample of urban textures of Rome and Barcelona. The study is parametric in approach. The textures were modelled and parameterized and their performances were compared. The UHI in different urban textures was calculated, by Urban Weather Generator tool. Then a sensitivity analysis of the building energy demand to the outdoor air emperatures and the incoming solar radiation was carried out, by EnergyPlus engine. Results confirm the relevance of urban morphology to the UHI intensity. Warmer temperatures lead to an average increase of energy demand from 10% to 35%, according to different urban densities. At the same time, the incident radiation reduction due to urban obstruction is desirable in Mediterranean climate; it allows a reduction of annual energy demand up to the 19% compared to an unobstructed environment. Therefore, relevant errors may occur if urban morphology’s contribution to energy demand is neglected, approximately 89% for space heating and 131% for space cooling calculations, depending on the texture density and the building orientation.Postprint (published version

Sustainability of compact cities: the SOS_UrbanLab activity

Urban development is facing new challenges to allow the evolution of the environment, in accordance to sustainability principles. In this context, decision makers have to answer to three main issues: how to intervene on the existing compact cities? How to combine and develop interventions on different scales? How to move from requalification to regeneration? The SOS_UrbanLab (Engineering Laboratory for Construction and Environmental Sustainability) researches, starting from a multi-scale analysis, propose a set of eco-friendly solutions to support the potential and capability of territories, integrating their benefits to reach a full sustainable approach

Urban morphology indicators for solar energy analysis

Within the variation of energy performance at urban scale, the relation between solar irradiation and urban form takes a central role. The solar availability on façades which is influenced by the morphology of the urban context, is strictly related to building energy performance indeed. In this paper, we aim at identifying a set of urban morphology indicators (UMIs) that show the most accurate relations with the solar availability on façades (SIy) in the Mediterranean context. The analysis that relates to 14 urban textures of Rome and Barcelona comprises seven UMIs: gross space index, floor space index, façade-to-site ratio, average building height, volume-area ratio, building aspect ratio and sky factor of building façades. The SIy in each texture has been calculated with Heliodon2 software, using normalised models; the relation between SIy and UMIs were investigated using least-square regression analysis. Results suggest that gross space index, façade-to-site ratio and sky factor show very good correlation with SIy (R2 = 0,91) and could be used to develop a comparative assessment tool of solar performance at fabric scale. This could ease the work of urban planners and architects in the early stage of design, reducing both data and time normally needed to perform solar analyses at urban scale