Thesis (M. Phil.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 50-54).

Thesis (doctoral)--Kungl. Tekniska högskolan, 1996.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

This project is mainly focused on the improving and design of the ventilation system of two rooms at different levels of a gym (Friskis and Svettis in Gävle, Sweden) to reduce the  concentration to never be higher than 1000 ppm. For this purpose, several field measurements were performed in different locations and situations. Two main measurements were necessary. On one hand, the  level in different parts of the rooms during different activities. On the other hand, the air flow through the inlet and outlet ducts of the ventilation system. It was also important to take into account the indoor temperature and humidity. These measurements were enough to analyze the failures of the system and to recognize the worst points of each room. Comparing both rooms, the necessity of changing the ventilation system in one of these rooms was much higher, due to there were measured  values up to 3000 ppm during a typical day in the gym. With this information the consequences of high CO2 levels in human people were analyzed. Among various ventilation systems, displacement ventilation system was proposed as the new design. Theoretical calculations were made to reach to the value of 31.8  in the air change rate (ACH), which was the necessary value for the new design to keep the carbon dioxide level under 1000 ppm.

The study of the buoyancy–driven displacement ventilation flows has been conducted earlier through both mathematical modelling and experiments. There can be some assumptions made in the studies for thermal analysis such as: adiabatic boundaries, neglecting radiation heat transfer between wall surfaces, and neglecting the absorptivity of the air on simulating the thermal distribution within the ventilated spaces. This study considers heat conduction at boundaries, heat radiation between wall surfaces and radiative absorptivity of the air when modelling buoyancy-driven displacement ventilation flows. The simulations were carrying out using computational fluid dynamic (CFD) programme Star-CCM+. This study investigates the influence of the absorptivity of the air on thermal distribution within an enclosure ventilated by buoyancy-driven displacement ventilation flows. Two cases of buoyancy-driven displacement ventilation experiments conducted early by Sandbach (2009) and Li et al. (1993b) were modelled. To consider the absorptivity of the air, the local weather data were retrieved and were used for calculating the absorption coefficient of the air under different weather conditions. The participating media radiation model was employed to compute the radiation heat absorbed by the air. In addition, the performances of the turbulence models on modelling buoyancy-driven displacement ventilation flows were investigated to ensure the predicted results were accurate and satisfactory. The simulation results presented in this study have shown to agree well with the experimental data in two different experiment cases. In the case of the experiments conducted by Sandbach and Lane-Serff (2011b), the predicted results match well with the measurements when considering absorptivity of the air. The errors between the simulation results and the measurements were less than 10% in most cases. The results also suggest that the absorption coefficient has an influence on ventilation flow rate and consequently has an effect on the strength of the stratification. This indicates that the absorption coefficient should be determined according to the conditions rather than be given an one-and-for-all value. The simulation results have also shown to agree well with the measurements given in the literature presented by Li et al. (1993b). The effect of the absorptivity was shown to be more significant in the case of high supply airflow temperature or high supply heat load. Hence, radiative absorptivity of the air should be taken into account in order to accurately model the thermal distribution in the ventilated enclosure.

This thesis reports a new set of experimental data and presents an in-depth analysis of the flow physics of a jet stream produced by a large quarter-round corner-mounted displacement diffuser. The air velocity, temperature and turbulence intensity inside the displacement ventilation (DV) jet have been thoroughly analyzed and compared with the reported findings of previous studies and model predictions. Furthermore, thermal comfort has been analyzed using the measured data following the ASHRAE standard. This thesis also aims at establishing an accurate numerical approach for simulating the heat and fluid flow in a room ventilated by a DV system. The supply boundary condition has been thoroughly investigated, which includes tests of the conventional box and momentum modeling methods, and proposal of a more accurate modeling approach. In addition, the predictive accuracy of the standard k-ϵ, RNG k-ϵ, SST k-ω and RSM turbulence models has been examined against the experimental data.

This thesis reports a new set of experimental data and presents an in-depth analysis of the flow physics of a jet stream produced by a large quarter-round corner-mounted displacement diffuser. The air velocity, temperature and turbulence intensity inside the displacement ventilation (DV) jet have been thoroughly analyzed and compared with the reported findings of previous studies and model predictions. Furthermore, thermal comfort has been analyzed using the measured data following the ASHRAE standard. This thesis also aims at establishing an accurate numerical approach for simulating the heat and fluid flow in a room ventilated by a DV system. The supply boundary condition has been thoroughly investigated, which includes tests of the conventional box and momentum modeling methods, and proposal of a more accurate modeling approach. In addition, the predictive accuracy of the standard k-ϵ, RNG k-ϵ, SST k-ω and RSM turbulence models has been examined against the experimental data.

Many airborne diseases such as Coronavirus variants are spread from person to person by indoor air movement. This is of particular concern in healthcare environments such as hospitals. There is a significant body of research that suggests that indoor ventilation strategies such as personalized ventilation systems my help reduce the spread of these viruses. While there are studies related to the efficacy of air movement from personalized ventilation, there are very few studies that explore how best to integrate these systems into the design process for hospital patient rooms. This study focuses on how to integrate personalized ventilation (PV) and displacement ventilation (DPV) systems into patient room design. The aims of this study are to first, develop a procedure using the Choosing By Advantages approach to make design decisions related to the implementation for personalized ventilation and displacement ventilation in private and semi-private patient rooms to prevent cross-infection. Secondly, using this approach, design solutions are proposed for patient room layouts with PV and DPV in different locations. The study proposes the best locations and components of the PV and DPV ventilation air supply and exhaust. Further practical models/simulation rooms are required to test the impact of PV systems on patients' and nurses' daily activities. / Master of Science / Many airborne diseases such as Coronavirus variants are spread from person to person by indoor air movement. This is of particular concern in healthcare environments such as hospitals. New personalized ventilation systems place ventilation air directly at the patient bed and consequently can reduce the spread of these viruses by effectively managing in-room air movement. This study explores how best to make design decisions for the implementation of personalized ventilation systems into hospital patient rooms. Applying this decision-making approach, design solutions are proposed that integrate personalized ventilation with commonly used displacement ventilation in patient rooms.

Battle Hall, located at the heart of the University of Texas at Austin’s campus since 1911, has been serving the University for a century. It was designed for cooling with natural ventilation prior to being fully air conditioned in the mid-1960s. The mechanical system currently installed in Battle Hall is over 40 years old. While it provides reasonable environment for the collections, it struggles to achieve stable conditions for various zones in the building. The purpose of this study is to consider isolating the Reading Room as an individual zone and explore the possibility of restoring natural ventilation as it was originally designed. There are various benefits in restoring natural ventilation to the hundred-year old Reading Room, including psychological benefits, indoor air quality, and energy savings. However, various concerns, such as environmental conditions, air pollutants, acoustic, and potential light damages, also exist. This study focuses on investigating the possibility of restoring natural ventilation by examining existing conditions, collection care requirements for library collections and historic architectural elements. Two data-loggers were placed in the Reading Room to record temperature and relative humidity readings for approximately five months. Through analysis of these readings of existing collection care settings and existing architectural settings, potential solutions and alternatives were considered and examined. These included non-action, hybrid natural ventilation, Johnson Controls Personal Environmental System, and HVAC shut-off. This study is the first of its kind for Battle Hall. As a Historic Structures Report of Battle Hall is commissioned by the University, this study provides a better understanding of potential solutions and alternatives to restore natural ventilation to Battle Hall. This may also serve as a platform to stimulate ideas and research on natural ventilation restoration to other buildings in the University. / text