Solar chimney for natural ventilation induction in buildings

Author(s)

Leticia de Oliveira Neves

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Civil, Arquitetura e Urbanismo
• Defense date: 2012-11-06

Examining board members

Maurício Roriz; Lucila Chebel Labaki; Doris Catharine Cornelie Knatz Kowaltowski; João Roberto Gomes de Faria; Fernando Marques da Silva

• Advisor: Maurício Roriz

Abstract

Natural ventilation is one of the most important strategies for passive cooling of indoor environments. It can occur by wind forces, by stack effect or by a combination of both strategies. The second choice can be more effective in urban areas, where there are obstacles that block or reduce significantly the wind speed. This research has the aim to analyze the potential of solar chimneys to promote natural ventilation in low rise buildings, located at typical climates of Brazilian territory. Experimental studies were developed, by means of the construction and monitoring of a test cell, under real climatic conditions, and the development of wind tunnel tests, using small scale models. Theoretical predictions were developed using a mathematical model adapted from literature and computer simulation. A calibration procedure was carried out, based on results obtained through the experimental set up. The procedure consisted in a comparative analysis of chosen variables, considering data of glass and absorber surface temperatures, air temperature and volumetric flow rate inside the chimney channel. Results confirm the great potential of applicability of the theoretical models on the performance analysis of solar chimneys, specially the computer simulation, which presented differences lower than 20% between measured and calculated results. Therefore, the simulation model was chosen to perform an analysis of the effects caused by the variation in geometric and constructive parameters of a solar chimney, including air channel depth, chimney length, solar collector tilt and type of glass used on the solar collector. It was also analyzed the possibility of using a chimney extension, which would be responsible to maintain a constant height between inlet and outlet openings, independently from the absorber inclination. Ultimately, the system performance was analyzed considering the combined effect of thermal and wind forces, for a specific configuration of solar chimney. Results confirm the great potential of applicability of solar chimneys as a passive conditioning strategy for low latitude locations. The proposed system with optimum inclination angle for maximum solar irradiation added to a chimney extension presented a significant enhancement of airflow rates, for the studied cities, with results between 40% and more than 100% higher than the results obtained with a solar chimney with inclination angle for maximum airflow, considering the pressure gradient inside the channel. It has been verified that the pressure losses inside the chimney have great importance in its performance, since it affects linearly the airflow results, being essential the correct prediction of these losses. Wind forces have a strong influence on the system's performance, even at low velocities. By comparing situations with no wind and with a 1m/s wind velocity, for example, it were obtained differences of up to 47% in the solar chimney volumetric flow rate, for a case study (AU)

• FAPESP's process: 09/02045-6 - Solar chimney for natural ventilation induction in buildings
• Grantee: Leticia de Oliveira Neves
• Support Opportunities: Scholarships in Brazil - Doctorate