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Auf Wissen bauen

AKUSTIK UMWELT, HYGIENE UND SENSORIK

ENERGIEEFFIZIENZ UND RAUMKLIMA

GANZHEITLICHE BILANZIERUNG HYGROTHERMIK MINERAL. WERKSTOFFE UND BAUSTOFFRECYCLING

URBAN ENERGY MODELING

Dr. Afshin Afshari afshin.afshari@ibp.fraunhofer.deManager, Urban Physics Modeling Group, Fraunhofer Institute for Building Physics (Germany) 12 Oct. 2020

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URBAN PHYSICS

• Replacement of vegetated landscapes with impervious materials

• Erection of large man-made structures• Intense human activity

• Storage of heat in high thermal mass structures• Radiation entrapment in high density areas• Obstruction of air flow• Reduction of evapotranspiration

• Urban heat island• Exacerbated impact of heat waves• Increased cooling load• Rise in air pollutant levels

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URBAN HEAT ISLAND (UHI)

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n The urban heat island effect is a result of urbanization, structural and land cover changes; it can result in temperature differences of up to 10C between cities and their surrounding rural areas

n UHI increases air pollution and greenhouse gas emissions (due to the greater use of air conditioning)

n Global warming is exacerbated in urban areas by the UHI effect

A/C Waste heat

n Entrapment of short and long-wave radiation in urban canyonsn Decreased long-wave radiative heat losses due to reduced sky-view factorsn Increased storage of sensible heat in the construction materialsn Anthropogenic heat released from combustion of fuelsn Reduced potential for evapotranspirationn Reduced convective heat removal due to the reduction of wind speed

Shortwave radiation

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BUILDINGS IN THE URBAN CONTEXT

nThe energy demand of a building in an urban area does not only depend on the characteristics of the building itself

nUrban heat island effects as well as interactions with the surrounding buildings at local scale do have an important effect on the energy demand of a building in an urban area

n In comparison to an isolated building, a building in an urban area experiences: n increased air temperatures due to the urban heat island effectn lower wind speeds due to a wind-sheltering effect

n reduced energy losses during at night due to reduced sky view factorsn altered solar heat gains due to shadowing and reflections n modified radiation balance due to the neighboring buildings

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ENERGY MODEL GRANULARITY

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MODEL-BASED URBAN DESIGN/RETROFIT

• Outdoor thermal conditions

• Energy use in buildings• Air pollution

Dynamic urban microclimate

model

• Buildings • Paved surfaces • Vegetation (including building-

integrated vegetation systems)• Anthropogenic heat

Bringing microclimate assessment into the realm ofiterative evaluation and optimization of design/retrofit

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MESOSCALE ANALYSIS

nMesoscale models incorporating the urban canopyparameterization aim to resolve the urban climatewith horizontal grid resolutions of several hundredmeters

n “Sub-grid” phenomena, such as micro-scale 3D flows or interactions with actual urban structures(roads, roofs, walls) are therefore parametrizedinstead of being modeled using applicable physicallaws

n The implementation of micro-scale models isnecessary if higher horizontal grid resolutions arerequired

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MICROSCALE ANALYSIS

nMicroscale Computational Fluid Dynamics (CFD) models consider the interactions between theatmosphere and the urban structures, withcomprehensive physics-based 3D flow analysis

nBoth meso- and microscale simulation approachesare computationally intensive, especially for longersimulation periods

n In a decision analysis context where, typically, multiple full-year simulations of the urban micro-climate are required another approach is needed

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DECISION SUPPORT FOR URBAN PLANNING

nUncoupled urban canopy models aresignificantly less computationally intensive thanboth meso-scale and micro-scale CFD models

nThe urban canopy model at the heart of thisthird modeling approach is similar to the urban parameterization implemented by meso-scalemodels; however, it is not coupled to a fullmeso-scale atmospheric representation

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n It is often driven, indirectly, by conditions measured at a nearby rural weather station(e.g., airport) via a simplified representation of the momentum/energy exchangesbetween the urban canopy layer and the surrounding atmosphere

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APPLICATIONS

nAnalysis of the impact of urban vegetation, green roof/wall, cool surfaces, photovoltaics on overall energy demand (national energy policy decision makers)

nUrban design/retrofit optimization (urban planners and municipalities)nClimate-aware building design (architects and building energy engineers)nHigh-resolution spatial mapping of the current or future urban heat island

(municipalities)nAvoidance of heat stress or air pollution (public health authorities)nEnergy production/distribution planning (energy utilities)

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CURRENT PROJECTS

nUrban Physics Modeling (main project, ATTRACT grant): Model-based decision support system enabling a priori assessment of the impact of: urban design alternatives, large-scale retrofits, minimum energy performance standards, demand-side management, district energy systems, tariff changes, etc.

n INCity TakeOff – Flying taxis in Ingolstadt: Development of a virtual city model tobe used as testbed for the climate simulation based on a CityGML description of the city

n IEA Annex 80 - Resilient Cooling: Assessment of the interactions of the air-conditioning system with the environment (e.g., impact on urban heat island, local air pollution)

nUC2-Propolis – CFD city climate simulation (Berlin, Stuttgart, Hamburg, Munich)11

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PAST PROJECTS

nMasdar City (2008-2011): Concept design and modeling of a smart and energy efficient city; sustainability KPIs and energy design guidelines

nAbu Dhabi Municipality (2012): Detailed energy audit and subsequent energy modeling of sector E3 in downtown Abu Dhabi (71 buildings)

nRegulation and Supervision Bureau (2013-2014): Time-of-use tariff experimentnExecutive Affairs Authority (2012-2014): Comprehensive Cooling Program (CCP)

n Remote fault detection and diagnosis of chillers and air-handling units n Life-cycle analysis of large-scale energy efficiency and/or urban heat island mitigation retrofits

nMasdar/MIT (2014-2017): Modeling of the intricate relationship between the urban microclimate and the built environment

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