Paper Conference

Proceedings of BauSim Conference 2010: 3rd Conference of IBPSA-Germany and Austria


Kombinierte Stadtklima- und Gebäudeenergiemodellierung zur Bestimmung des Energiebedarfes von urbanen Gebäude

Fazia Ali-Toudert

Abstract: The present paper addresses the necessity of coupling urban climate and building energy models when investigating the energy demand of urban buildings. Indeed, the energy demand of buildings is still often assessed with the assumption of an unobstructed free horizon although this approach, valid in rural sites, is not applicable in dense urban structures for two main reasons: i) the surrounding urban microclimate differs from the standard weather data (e.g. TRY) and ii) the mutual obstructions between buildings decrease the sunlight and daylight potentials and hence the passive solar gains which are decisive in the building energy balance. As well, the climate and the building construction themselves affect the interactions between outdoor and indoor microclimates through the built envelope being a shared interface. This paper addresses the following issues: a. How the urban structure modifies the microclimate outdoors, and how would this “new” microclimate affect the heating and cooling energy demands of the building? b. What are the effects of urban geometry and plan density in combination with solar orientation on the energy demand of an urban building? c. To which extent are building describers like façade thermal insulation, thermal inertia, window ratio, etc. also decisive? The numerical method used combines the urban canyon model TEB, and the building energy model TRNSYS 16.1. By means of an extensive parametric study several urban structures are investigated where the effects of the following factors are explored: i) urban context (aspect ratio and solar orientation), ii) building construction (window ratio, thermal insulation and thermal inertia) and iii) climate type: the European mid-latitude location of Mannheim, 49.21 °N and 2 north-african subtropical locations: the hot-humid Algiers 36.34° N and the hot-dry Gharadia 32.24° N. Target quantities addressed in this paper are heating and cooling loads which are analyzed statistically on the basis of the design of experiments DOE method. The results basically confirm the significance of all the variables investigated, with dominance of some combinations of aspect ratio, thermal insulation, thermal inertia and window ratio. 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, especially for the subtropics. Heating net energy demand is in contrary reduced for the same reasonm in particular for Mannheim. 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. Building Performance Simulation in a Changing Environment - A. Mahdavi / B. Martens (eds.) - 79 Third German-Austrian IBPSA Conference Vienna University of Technology
Pages: 79 - 85