Ventilation performance of a solar chimney in naturally ventilated multiple chambers
Creators: name: Zhang, Haihua
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400504
subject: Construction engineering

description: Due to the potential benefits of passive ventilation systems in economic and energy conservation, resistance against noise, and reduction of carbon dioxide emission, passive strategies are increasingly being advocated as low-energy alternatives and low-cost solutions for energy conservation buildings. According to local climate conditions and building characteristics, passive ventilation systems show different airflow characteristics and temperature distributions. Some thoughtfully designed passive ventilation systems could achieve natural ventilation and space heating/cooling following different airflow patterns during the cooling and heating seasons. 

Solar chimney (SC) is a passive solar design feature used to improve natural ventilation and indoor air quality. It consists of a vertical shaft or duct that connects the interior of a building to the outside. As sunlight heats the air inside the chimney, the warm air rises and is expelled through the top of the shaft, creating a vacuum that draws cooler, fresher air into the building from lower openings or vents. This process effectively regulates indoor temperature and promotes air circulation without relying on mechanical systems. 

This work has conducted a series of studies aimed at exploring the potential of solar chimneys (SCs) as a natural ventilation technique in multi-chamber buildings. It focuses herein on examining solar chimneys' ventilation capacity when integrated into multi-chamber and multi-storey buildings, which has not been thoroughly studied previously. Previous studies have mainly focused on solar chimneys in single-room or single-floor buildings, lacking theoretical development for multi-chamber or multi-storey buildings. The focus is on examining the airflow characteristics inside a wall-mounted solar chimney cavity and the attached ventilated zones under various configurations and external environments. 

First of all, this work carries out numerical simulations for single-floor with double chambers to evaluate the SC's performance in different building configurations and provide recommendations for optimizing its effectiveness. The critical geometrical parameters of the solar chimney and building layouts are suggested based on the trade-off between the buoyant flow patterns and the volumetric flow rate by conducting numerical simulations. The airflow characteristics and the solar chimney performance in relation to various configurations and external environments are examined. The results show that increased chimney height and inlet location can significantly improve the airflow rate. A maximum airflow rate of 0.22 m3/s is observed for a solar chimney with a cavity gap and inlet size of 0.2 m. The multiple rooms with different aspect ratios have a limited impact on the ventilation performance, with a fluctuation of 5% in volume flow for four groups of room layouts. The velocity distribution of the long and narrow room layout shows an improvement in the airflow rate. The results show that a wall solar chimney has the potential to provide effective ventilation for multi-chamber buildings.

Subsequently, this work looks at the thermal response and airflow characteristics within naturally ventilated multi-storey buildings. It presents the development of a theoretical model for assessing solar chimney assisted buoyancy-driven natural ventilation effectiveness. Three mathematical methods are introduced to predict the ventilation rates for each floor explicitly based on the closed flow loop method. Comparing the methods, Method 1 is suitable for two-storey or single-storey cases. Method 3 is practical for those greater than two-storey. The results show that a wider cavity gap and a higher stack height for a multi-storey solar chimney are the most effective ways to optimize the ventilation rate. The solar chimney dimensions have a more significant effect on the volume flow rates than the solar radiation intensity. This work establishes the links between single-room and multi-storey theoretical models. It provides practical mathematical methods to predict ventilation rates for a solar chimney in a multi-storey building. 

This work further develops a novel correction factor for solar chimney assisted natural ventilation in multi-storey buildings and presents how the number of stories in a building affects the performance of the solar chimney ventilation. The storey correction coefficient is proposed to predict the SC-induced ventilation at various storeys with identical air inlet areas. This work uses a combination of theoretical analysis and numerical simulations to study the effect of different numbers of stories on the system's performance and provide guidance on how to optimize its effectiveness in buildings of varying parameters. The theoretical model is established to elucidate the relationship between ventilation flow rates, solar radiation intensity, vent sizes, and storey number, and the results are validated through numerical simulations. The findings show that the total SC ventilation performance is enhanced with the increasing height of a building. However, its enhancement with a higher chimney cavity is less effective for further increasing the storey number due to the taller chimney cavity hindering the ventilation performance of the lower floors. The top floors' volume flow rate decreases exponentially as the storey number increases. The cavity gap should increase gradually as the storey number increases to maximize the total flow rate. It reveals that the overall volume flow rate is sensitive to the cavity gap changes. This work is the first to address the influence of the storey number on ventilation rates for multi-story solar chimney buildings. It provides practical mathematical methods to predict ventilation rates for each storey. The findings of this study contribute to the practical application of solar chimneys in multi-storey buildings.

Ultimately, this work extends the theoretical model of a single room to multiple floors and proposes practical mathematical methods to obtain acceptable prediction accuracy of ventilation rates for a solar chimney in a multi-storey building. The significance of this work lies in its potential to provide technical support and serve as a reference for the practical application and experimental design of multi-storey or large-scale buildings. This work aims to bridge the gap between theoretical approaches and their real-world application by offering practical insights and recommendations for designing solar chimney-assisted naturally ventilated buildings with multi-chamber or multi-storey. It contributes to a deeper understanding of the performance of the solar chimney system in multi-chamber buildings and sheds light on how influencing parameters affect ventilation capacity. This work also provides a resource for architects, engineers, and other building professionals who are looking to incorporate sustainable solutions into their designs.