Juniorprofessur Energieeffizientes Bauen

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    A multi-scale and GIS-based investigation of climate change effects on urban climate and building energy demand for the city of Stuttgart
    (2019) Ali-Toudert, Fazia; Ji, Limei
    This paper presents a multi-scale and GIS-based investigation approach whose goal is to quantify the consequences of a climate change scenario (2041-2050) on the energy demand of buildings by comparison to a past scenario (1991-2000) applied to the city of Stuttgart. Energy simulations are made at building scale while taking into account the surrounding urban microclimates. The investigation method combines 1) numerical modelling using TEB and TRNSYS, 2) design of experiments (DOE) statistical analysis for data pre- and post-processing, and 3) GIS techniques. The outcome of the study is the heating and cooling energy demands summed up at city block level and displayed in 2D GIS maps. The results reveal that i) warmer urban microclimates occur, ii) with less heating and more cooling of buildings required if future versus past reference climate data are used. Spatial differences in the results within the city are found depending on the geometrical and thermal characteristics of the individual city blocks and buildings.
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    Energy performance of buildings under urban conditions : Theory and application with focus on urban climate and building construction
    (2017) Ali-Toudert, Fazia
    This research intends to be a contribution in fostering the interdisciplinary work on climate and energy issues with focus on buildings explicitly located in urban areas. It seeks to explore the link between urban and building physics to characterize the interdependences between outdoor and indoor climate and the impact on the resulting energy demand of buildings. The work addresses two key issues: First, it aims to understand how urban microclimates evolve hence focuses on identifying the part of responsibility urban and building thermo-physical attributes have in modifying the urban energy balance fluxes, surface and air temperatures as well as the formation of canopy heat and cool islands. Secondly, it assesses the consequences of these modified urban energetics and thermal conditions on the energy performance of buildings subject to these boundary conditions. The research method relies on numerical modelling for its speed and versatility, and combines four components: i) the Town Energy Balance Model TEB for the urban microclimate prediction, with ii) the non-stationary building energy model TRNSYS for simulating the thermal behaviour indoors and the resultant energy demands for ensuring thermal comfort, iii) the statistical design of experiments method DOE for handling the complexity of the task by providing systematic exploration plans, and iv) additionally the GIS techniques, applied to a spatially extended real city for the pre-processing, post-processing and mapping of urban climate and energy demand results. The work consists of two complementary parts with different objects of study. PART I deals with theory-based urban office buildings and PART II addresses the city of Stuttgart as real case study. Both investigated objects are located at a European mid-latitude for which representative boundary climates are utilized. For the theoretical office buildings, a test reference year (TRY12, Mannheim) of the German weather services DWD is used. For Stuttgart, long-term weather recordings for 10 years (2003 - 2012) are available for use. For comparison purposes regarding the influence of the climate type, additional calculations are carried out for the Mediterranean and warm location of Algiers. In PART I, extensive parameter studies (including sensitivity analyses) are conducted with the aim of exploring the mechanisms underlying the formation of urban microclimates. Decisive urban and building thermo-physical indicators are varied. Urban canyon-like structures with various solar orientations are simulated. Building constructive features including window ratio, thermal insulation, thermal inertia, in addition to the shortwave albedo and longwave emissivity as radiative surface properties are investigated. The effects of further settings related to the building use and operation are also checked. The target key metrics are the energy balance fluxes at the canyon facets, the surface and air temperatures within the canyon, as well as the resulting indoor energy demands for heating, cooling, lighting and ventilation. For comparison, the building simulations are run under standard and urban climate conditions in order to isolate the role of the urban microclimate on the energy demands. The results are discussed for the building as a whole as well as for the floors and façade’s orientation with reference to the view factor implied by the urban canyon vertical profile. PART II employs the same investigation method using Stuttgart city as case study. The focus of the calculations is placed on the possibly highest spatial resolution downscaled to the single building. Using 2D and 3D city maps and further statistics about the buildings, thermally relevant indicators for buildings and city blocks are calculated by means of GIS. The peculiarity of this approach draws on the generic and abstracting modelling of the thermally relevant properties of the buildings instead of describing them using their real physical attributes. On the one hand, this procedure enables the feasibility of the task in keeping the processing time manageable. On the other hand, it allows for subsequent transferability of the results using statistically determined mathematical models. This work confirms the importance of all investigated variables and provides a hierarchical quantification of their influence on both urban microclimate and building energy demands. In particular, the anthropogenic heat, the canyon geometry, and the thermal inertia appeared to have evident effects on the magnitudes and the time course of the warming or cooling of the canyon air. Under urban microclimate conditions, the cooling increases owing to dominating canopy heat island effects, whereas the heating demand mostly decreased for the same reason. The building simulations in PART I show that the effect of the microclimate is highest in the case of thermally weak insulated building envelope with largely glazed façades. The massive construction also appears to be more advantageous than the lightweight construction. For the simulation settings assumed, the useful energy demand under urban microclimate conditions for heating and lighting decreases, whereas the energy demand for cooling and ventilation increases in comparison to standard climate conditions. The reduced sky view at street level affects negatively the energy demand for heating and lighting because of the diminished potentials for solar and daylight potentials, whereas the need for cooling and ventilation are reduced. In total, lower floors are disadvantaged in comparison to upper floors. The comparison with the Mediterranean climate shows similar energetic behaviour outdoors as well as indoors regarding the relevance and effects of the investigated variables. However, the daily cycle and magnitude of the urban microclimate changes are different. Indoors, the share between heating and cooling are reversed, leading to a different pattern of the total energy demand. The investigation of real conditions at Stuttgart city reveals a number of challenges. For time processing reasons, the extensive results about the urban microclimates must be reduced to a few climate clusters in order to be used in the subsequent building simulations. Moreover, the accurate modelling of the city structure and buildings is partly hindered by the lack of detailed row data, even though it is technically possible. Nevertheless, the comparison of the calculated energy demands against recorded consumption data for heating shows good agreement and confirm thereby the pertinence and practicality of the generic modelling applied. Finally, this research demonstrated the suitability of combining TEB, TRNSYS, DOE and GIS in handling these interdisciplinary tasks. However, it also points out the necessity of developing an integral urban – building energy model for improving the prediction accuracy and reducing the time costs. The first milestone of such a model in form of TEB version for use within the TRNSYS environment is presented in this work. The so-called TEB – Type 201 solves numerous practical issues and improves the user friendliness and processing capabilities of the original TEB. The synchronised urban – building energy model in outlook must include the feedback loop between indoor and outdoor microclimate via the shared building envelope at each time step, thereby implementing an interdisciplinary approach, which will bring substantial knowledge from urban climatology and building science operationally together.