Qualitative modelling of the natural ventilation potential in urban context

Abstract

The two objectives of natural ventilation in buildings are the improvement of indoor air quality and thermal comfort. The methodology proposed hereafter provides an assessment of the natural ventilation potential for indoor air quality, while taking into consideration the other objective. More precisely, requirements on comfort impose the appropriate ventilation strategies to be applied for each given meteorological situation. On the basis of these strategies, the methodology evaluates the appropriateness of a given location to natural ventilation. After a historical introduction (Chapter 1), the statement of the problem (Chapter 2) and a review of the state of the art (Chapter 3), Chapter 4 presents a novel methodology to assess the natural ventilation potential starting from its driving forces (wind-induced and buoyancy-induced pressures) and from its constraints (noise pollution and atmospheric pollution), which applies multicriteria analysis. The method uses the results of the atmospheric simulation model Lokal-Modell (LM, described in section 3.4). The related software tool, developed within the European project Urbvent, and tested against real cases, is presented as well. Chapter 5 gives a view of the results of an atmospheric mesoscale model, referred to as Finite Volume Model (FVM), that includes an urban module (described in section 3.6) allowing to compute the effects of the urban tissue on meteorological parameters. This model has been adapted as part of this work to use the outputs of the above-mentioned Lokal-Modell (LM) as boundary conditions. (To this end, previous works utilized NCEP/NCAR Reanalysis data, with an original spatial resolution 40 times lower than LM in latitude, 25 times lower in longitude and 6 times lower in time.) After a verification of the urban model results against on site measurements carried out in the Basel region (Switzerland) over a summertime period, Chapter 6 presents the utilization of these results within the Urbvent method of Chapter 4. The ensuing potential for natural ventilation is the object of a verification resorting to an air pollution exposure study (Expolis) in section 6.4. Attention is drawn to the fact that it has been decided to assess the natural ventilation potential of the site itself, in the most building-independent way. In so doing, an analysis of the results can tell what type of ventilation a given site is suited for and what kind of building should be built there (or how to refurbish an existing one). Put another way, the model examines whether external conditions required for applying natural ventilation coexist. How to properly design a building taking advantage of theses conditions is not addressed here. This is left to the reader or to the designer. Incidentally, the bibliography dealing with this very topic is quite abundant.