City, Wind, Energy: the Limits for Applying Natural Ventilation for Energy Conservation Towards the Urban Densification in Hot Humid Climate

Abstract

It is widely known that urbanization can deeply compromise the city’s atmosphere through the modification of the environmental parameters. Among the city’s impacts over natural climate, great emphasis is placed on heat generation and changes on natural ventilation conditions that directly lead to thermal discomfort, compromising buildings energetic performance. Currently energy consumption is in the centre of the discussion about environmental preservation and sustainable development. Within the buildings it is emphasized the use of natural resources for building’s conditioning. Specifically in cities with hot, humid weather, the case of Fortaleza, Ceará, Brazil (latitude 3° 43’ S), natural ventilation is the main passive strategy to obtain thermal comfort.
Therefore it is fundamentally necessary to understand the physical phenomenon and the aspects that influence natural ventilation process to objectively use the wind potential for cooling of buildings. On the other hand, it is becoming a major problem to maintain the potential to naturally ventilate the building’s façades in urban centers because of the constructive densification and building’s height, compromising the wind access to habitations. Based on existing standards air velocity should not exceed 0,2 m/s, otherwise it will compromise thermal comfort. However, latest researches about thermal comfort mechanisms in naturally ventilated buildings have shown that occupants of those buildings may prefer higher air velocities. The airflow around buildings creates a pressure distribution over buildings façades, an essential aspect to natural ventilation process. By creating high and low pressure zones over different parts of the building, the wind induces the air movement inside the building and once the city’s spatial organization directly influences building’s natural ventilation through the modification of pressure coefficients (Cp) over its surfaces, this research aims to determine the limits to urban densification in ways that it results in better conditions to the air movement in high-rise apartments. The study uses a Computational Fluid Dynamics (CFD) tool to analyze the airflow around buildings and inside the apartments, calculating velocity, pressure and flow. The objective is to adopt a set of urban and architectural solutions in order to dissipate the heat and improve indoor thermal conditions using natural ventilation, reducing the need for artificial conditioning.