Natural ventilation for office building retrofit in dense urban context under hot and humid climate

Leopoldo Eurico Gonçalves Bastos,Marilia Ramalho Fontenelle,Sylvie Lorente

doi:10.1590/s1678-86212021000200515

Abstract

Abstract Recent studies underline that simple and non-invasive retrofit solutions can recover natural ventilation potential in existing buildings under temperate climate. Nonetheless, the efficiency of these solutions in dense urban contexts under hot and humid climate remains unclear. This paper aims to evaluate the thermal comfort gains caused by natural ventilation when retrofitting an office building in downtown Rio de Janeiro. Computational Fluid Dynamics (CFD) and thermal simulations are carried out on Ansys CFX and Design builder to assess indoor air flow before and after retrofit. The diagnosis of the current scenario indicates that the surrounding buildings block a significant part of the wind flow, and occupants experience only a few hours of thermal comfort during the year, especially on lower floors. To increase indoor air flow, the fixed upper windows were transformed into pivot windows and kept open permanently. This measure increases the annual hours of thermal comfort by 0.5-35%, depending on the floor and the adaptive comfort model. These findings suggest that natural ventilation itself may not be sufficient to ensure occupants' comfort throughout the year under the investigated context.

Highlights

Several studies demonstrate that city densification contributes to reducing urban environmental quality (LEITE, 2008; NG, 2010; GONÇALVES et al, 2011)
The lack of green areas and the increment of surfaces’ solar absorbance, anthropogenic heat, and urban canyons are just some factors that induce the heat island effect (NAKATA-OSAKI; SOUZA; RODRIGUES, 2016; ALCHAPAR; PEZZUTO; CORREA, 2018), which can increase the air temperature in 15 oC compared to rural areas (SANTAMOURIS et al, 2001)
In order to fill the underlined gaps, this paper aimed to evaluate the thermal comfort gains caused by natural ventilation when retrofitting the windows of an office building in a dense urban area under hot and humid climate

Summary

Introduction

Several studies demonstrate that city densification contributes to reducing urban environmental quality (LEITE, 2008; NG, 2010; GONÇALVES et al, 2011). The lack of green areas and the increment of surfaces’ solar absorbance, anthropogenic heat, and urban canyons are just some factors that induce the heat island effect (NAKATA-OSAKI; SOUZA; RODRIGUES, 2016; ALCHAPAR; PEZZUTO; CORREA, 2018), which can increase the air temperature in 15 oC compared to rural areas (SANTAMOURIS et al, 2001). The expansion of high-rise buildings with reduced spacing tends to minimize the urban fabric air porosity (GONÇALVES et al, 2011; TORK; TIBIRIÇÁ; TIBIRIÇÁ, 2017). Air velocity and the differential pressure between facades are reduced, and stagnation zones become predominant in urban areas (NG; WONG, 2005; FONTENELLE; LORENTE; BASTOS, 2015). Santamouris et al (2001) attest that in certain regions, air velocity is reduced by up to 10 times. Hu and Yoshie (2013) underline the channeling effect produced by an air flow parallel to the street axis in uniform building height arrays

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