Enhancing Thermal Comfort in a Room Using Natural Ventilation, Phase Change Materials and Green Wall Biofilters
- Publication Type:
- Thesis
- Issue Date:
- 2019
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Natural ventilation is the process of supplying and removing air through an indoor space by natural means. There are two types of natural ventilation occurring in buildings: wind-driven ventilation and buoyancy-driven ventilation. Efficient design for natural ventilation in buildings should implement both types of ventilation. Furthermore the architectural design of the windcatcher inlet affects its performance and influences the occupant’s human comfort. Combining the wind-driven and the buoyancy-driven ventilation will be investigated in this study using a windcatcher natural ventilation system. The effect of the windcatcher’s inlet design is also investigated to achieve better air flow and to increase the efficiency of windcatchers. Experimental studies of windcatcher systems are very costly and mostly impossible in practice. CFD (computational fluid dynamics) tools will be used in this research to simulate the air flow through a two sided windcatcher. Two dimensional and three dimensional simulations are performed using Ansys Fluent and CFD Ace + to obtain quantitative and qualitative analysis of velocity magnitude, flow patterns and ventilation flow rate.
Furthermore, the increased pollution levels in cities highlights the importance of innovative strategies that can help to improve the quality of air introduced into buildings.
Green walls have recently been used to help with this and even thermal comfort. Enhancing the flow distribution and air flow rate through active green wall modules will be studied in this research considering the different parameters involved such as module geometry, moisture content, growing-medium-plant-roots mix and plant type. The current work represents a detailed assessment of airflow through an active green wall module. Airflow distribution through the module, the effect of wetting the substrate, and the effect of introducing a cover to the module’s open top face were investigated, with the aim to improve the module’s design and achieve more appropriate and effective airflow. Four cases of both planted and unplanted modules under both dry and wet conditions are considered. This work’s primary observation is that 𝘮𝘰𝘳𝘦 air will pass through a typical green wall substrate, and hence become cleansed, when the substrate is saturated wet more than when it is dry. The increase was substantial at approximately 50% more with 14.9 L/s total air flow rate passing through the wet planted module versus 10 L/s when dry. Reducing the 15.5 % of airflow passing through the module’s open top face was found to be essential to maximize the bio-filtration capacity. Adding a top cover to the module having six 10 mm holes for irrigation decreased the airflow through the top by 6 %, and directed it through the filter increasing the percentage of air flow passing through the front openings from 79 % to 85 %.
The effect of green walls on thermal comfort (Temperature and humidity) is also experimentally investigated. For the active modules, lower temperatures in the range of 1 to 3 °C, along with increased humidity levels have been observed when modules are saturated wet, similarly passive modules provided lower temperatures in the range of 0.5 to 2 °C. None of the plant species studied showed any preference, indicating that the moisture content of the substrate plays the major role affecting the temperature and humidity variations.
The effect of using phase change material (PCM) as a passive cooling technique on the performance of a windcatcher to meet the demand for thermal comfort, hence energy conservation and savings purposes, is studied in this research. Incorporating PCM located in the floor, ceiling and walls of a room as well as in the windcatcher’s inlet channel has shown the best performance. This set up provided a significant reduction of temperatures during the discharging process of about 3.61 ºC (equivalent to 9.33%) and an increase in the average temperatures of 3.40 ºC (equivalent to 15.70 %) during the charging process (solidification of PCM) compared with an empty room with no PCM. The effect of PCM on humidity was not significant as variations of maximum 3.88% is observed when PCM is used.
The ultimate aim of this research is to develop a natural ventilating system to enhance a healthy, comfortable and energy efficient indoor environment; PCMs and green wall modules are appropriately incorporated.
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