The environmental performance of urban building
Zusammenfassung der Projektergebnisse
This research investigates the role of the urban context including the urban climate and the solar access potentials in modifying the energy demand of urban office buildings. The investigation method relies on numerical modelling. The urban model Town Energy Balance TEB is combined with the building energy model TRNSYS in order to assess these thermal and energetic interdependences outdoor-indoor. Extensive parametric studies are performed, which results are analysed statistically according to the design of experiments method. Briefly, the work consisted in: running and analysing large sets of numerical simulations including: i) urban climate prognosis, ii) sensitivity analysis of TEB model, iii) Building climate prognosis with TRNSYS 16.1 using standard climate data first and then urban climate data, then, in extending the capabilities of the building energy model TRNSYS to urban climate issues by embedding an urban canyon model as TRNSYS-Type The focus was put on three contrasting climates, mid-latitude temperate Mannheim (Germany), and warm-humid and hot-dry subtropical locations of Algiers and Ghardaia (Algeria). The results of the EPUB project confirmed the hypothesis that the use of standard climate data in case of buildings located in urban context is not valid. The urban climate is being modified by the urban density, building construction and materials. Urban air temperatures can be by ± 5 Kelvin higher or lower than standard climate data with a clear trend to warming. Hours with a deviation of ± 1 - 2 K are dominant. Urban heat island effects were found and take place at times of year which are in good agreement with the literature on the subject, i.e. mostly in the evenings and night-time during the summer. Cool islands were also found especially in the morning hours when the sun is low. The high variability in time of the UHI already known from the literature is also confirmed by the simulations. This clearly argues for non-stationary modelling rather than the simple assumption of a constant increase in the air temperatures. As a consequence and as far as energy demand is concerned, the importance of adjusting air temperatures according to urban context including the vertical profile geometry, urban density and building materials has been demonstrated. The cooling net energy demand is found to be higher when urban air temperatures are used instead of standard climate data as direct consequence of dominating urban heat island effects. This is especially true for the subtropics where the solar radiation is intense and the sun position rather high. Heating net energy demand is in contrary reduced for the same reason, i.e. heat island. This is particularly visible for the temperate climate of Mannheim which needs are mostly for heating rather than for cooling. Hence, the total net energy demand as sum strongly depends on the site climate, namely whether the dominating needs are for heating or for cooling. The results also confirm the significance of all the variables investigated, with dominance of some combinations of aspect ratio (A), solar orientation (B), window ratio (C) thermal insulation (D), and thermal inertia (E). For the temperate Mannheim building describers (C, D, E) are the most important whereas for the warm subtropics the effect of the urban describer (A) is visible as well. Moreover, the analysis with focus on the urban geometry (vertical shape) showed e.g. in case of lighting that the openness to sky of the building affects its potential to use daylight. Due to the operation or not of the shading devices the final picture regarding daylight is influenced since both sun protection and daylight use are conflicting issues especially in the summer. Worthy of note is also recent investigations of other authors on similar issue during the project’s life, which have dealt with the subject from different perspectives, and which clearly confirm the relevance of the goals announced by EPUB. The strengthen of EPUB in this regard is its method with the combination of two models which enabled a fine prognosis of the target keymetrics at hourly basis (e.g. urban air temperatures, heating, cooling and lighting energy and lighting demand quantities). One further plus-value of the project is methodological. The method used revealed to be time-consuming because of the manual combination of two calculation models and a solution to overcome this problem has been proposed in form of coupled urban – building numerical modelling. Hence, an attempt to extend the capabilities of TRNSYS has been tested and a new type for TRNSYS has been developed within the project which enables to prognosticate the urban microclimate after TEB scheme prior to building energy simulation with TRNSYS. A prior literature review shows that this coupled modelling approach is still relatively new since only few initiatives are reported and further development of this new model is the main outlook of the project.
Projektbezogene Publikationen (Auswahl)
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2009. Energy Efficiency of urban buildings: Significance of urban geometry, building construction and climate. International Conference on Urban Climate, Yokohama, Japan, Jun. 29 - Jul.3 2009
Ali-Toudert F
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2010. Heating and cooling energy demand of office urban buildings in the subtropics: relevance of the urban microclimate, urban geometry and building construction CLIMA2010, Antalya, Turkey, 9-12.05.2010
Ali-Toudert F
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2010. Kombinierte Stadtklima- und Gebäudeenergiemodellierung zur Bestimmung des Energiebedarfes von urbanen Gebäuden. International Building Performance Simulation Association IBPSA-Conference, 22.-24.09.2010, Vienna, Austria
Ali-Toudert F
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2010. Sensitivity Analysis on the Effects of Urban Structure Properties on the Urban Microclimate and Energy Demand of Urban Buildings. 6 pp. World Renewable Energy Congress XI. 25-30 September 2010, Abu Dhabi, UAE
Ali-Toudert F
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Openness to the Sky as Indicator for Daylighting Potential of Urban Office Buildings in a European Mid-Latitude Location. International Conference on Climate and Constructions. 27-35. 24-25 October 2011, Karlsruhe, Germany
Ali-Toudert F
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Energy performance of buildings under urban conditions – Theory and application with focus on urban climate and building construction. Habilitation thesis, 2017,pp 333, TU Dortmund University.
Ali-Toudert Fazia
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Urban microclimate prediction prior to dynamic building energy modelling using the TEB model as embedded component in TRNSYS. Theoretical and Applied Climatology, Vol. 134. 2018, pp. 1413–1428.
Ali-Toudert, Fazia, Böttcher, Sven
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Exploration of the thermal behaviour and energy balance of urban canyons in relation to their geometrical and constructive properties. Building and Environment, Vol. 188. 2021, 107466.
Ali-Toudert, Fazia
