Pedestrian-level ventilation in an urban environment adjacent to a river channel: A case study for Bucharest city – Romania

Adrian Ciocănea,Andrei Dragomirescu,Bogdan Tofan,Mihai Toti,M.C Balan,A Georgescu,C Croitoru,I Nastase,C Georgescu,F Bode,A Dogeanu,M Sandu

doi:10.1051/e3sconf/20198507007

Abstract

Increasing evapotranspiration in cities, derived from vegetation and water bodies, can effectively mitigate the effect of urban heat island (UHI). This paper presents a study on an urban ventilation solution for Bucharest City in Romania. The solution is based on lifting air volumes from the free surface of Dambovita River, which crosses the city center where UHI has a significant impact, to the roadway and pedestrian level by using cross-flow fans mounted on floating panels planted with vegetation, which are placed at the river banks. The electric motors of the cross-flow fans are powered by PV solar cells. The real optimal value of evapotranspiration (ETRO) was computed for the case of lucerne in order to assess the air temperature at the surface of the floating panel and a numerical study was performed in order to obtain the velocities of the air flow and the temperature field in a domain containing the free surface of the river, the floating panel surface, and the roadway surface (at pedestrian level). It was observed that, at low flow rates, the cooler air reaches the roadway surface in a compact jet due to the Coanda effect - the coherent air jet is of about 30–40 cm above the ground level. For a day with clear sky and no wind conditions a decrease in the air temperature of 4–5 °C can be obtained at the pedestrian level, within a layer of 1 m height. The study opens the possibility to approach such issues at a greater scale in order to assess the viability of appropriate solutions for cooling down the urban heat island as well.

Highlights

The reduced air motion at pedestrian level decreases the air quality due to the weak natural ventilation that causes pollutants to accumulate at the ground level
This negative effect is enhanced by the urban heat island (UHI) which contributes to a change in the air temperature of up to 8–10 0C in a city center compared to rural regions
This paper presents a solution for the ventilation of the pedestrian level, which uses a combined method that consists both in increasing the green area available near a river bank, to enhance the evapotranspiration process, and in lifting air volumes from the free surface of the river using cross-flow fans powered by photovoltaic solar cells

Summary

Introduction

The reduced air motion at pedestrian level decreases the air quality due to the weak natural ventilation that causes pollutants to accumulate at the ground level. The strategies proposed to increase the outdoor air quality (OAQ) were focused on general solutions for decreasing the UHI effects, such as the minimization of heat emissions due to energy consumption [1,2] or the increase in the vegetation quantity and the albedo [3,4,5,6] using porous materials for street and pavement covers [7,8,9,10] Under these circumstances, it results that, on the one hand, shading from trees and the evapotranspiration process are the main natural factors that contribute to the cooling effect and, on the other hand, the usage of new materials with porous characteristics, bright colors, and favorable thermal properties is the anthropic factor that must be addressed. The case study is presented for Bucharest City in Romania, which is crossed by Dambovita River

Methodology

Calculation the value of the potential evapotranspiration

Findings

Conclusions