Theoretical and numerical studies on transport of gaseous contaminants in ventilated indoor environment

摘要

As far as indoor air quality (IAQ) is concerned, there are three types of airborne contaminants: gaseous contaminants, particulate contaminants and biological contaminants, and gaseous contaminants are the smallest as well as the most common type in indoor environment. In literature of the past several decades, many remarkable jobs have been done on studying and simulating the transport behaviours of some particular gaseous contaminants (such as formaldehyde, carbon monoxide, VOCs, etc.) in indoor environment. The research area pertaining to IAQ and HVAC is quite mature in terms of the large archive of journal articles as well as industrial standards in many countries that have been made and revised for many decades. However, there are still some important issues regarding transport of gaseous contaminants in ventilated indoor environment that have not been fully investigated or have been overlooked in current literature. This thesis has aimed to identify and investigate unchartered waters in this research area and tries to make contributions to the knowledge base of IAQ & HVAC. This thesis has taken both theoretical and numerical approaches. As for numerical approach, underlying method has been validated by experimental data from literature. Studying on different issues pertaining to gaseous contaminants, this thesis has provided some insights into the common features of the transport behaviour of gaseous contaminants in indoor environment. Through theoretical as well as numerical approaches, this thesis has concluded that, as far as steady state is concerned, all gaseous contaminants could be treated the same way in CFD simulation with respect to their diffusivities as long as some ventilation/convection exists in the indoor spaces. When time is considered, the difference created by diffusivity could quickly disappear if certain amount of ventilation exists. Moreover, as it will take time for gaseous contaminants to cumulate in indoor environment, this thesis has worked out a theoretical model to describe such time-dependent process, and then verified this formula by CFD simulations. This theoretical model leads to a demand control ventilation strategy for short-occupied rooms. Such strategy could significantly cut ventilation rate while maintain the required indoor air quality. This thesis has also investigated the influence of internal momentum sources (such as computer fans) to the transport of gaseous contaminants in ventilated indoor environment. Under the influence of computer fans, the indoor airflow field, temperature field and the concentration field of gaseous contaminants could be significantly changed. CFD simulations show that computer fans is an important driving force in indoor environment therefore should not be ignored in CFD simulations. Finally, considering many office rooms have no right to alter ventilation system, this thesis has showed examples by CFD simulations on how to adjust interior layout to achieve better air quality in breathing zone. This thesis has demonstrated that CFD is a powerful method to find optimal solution to IAQ issues. Results and conclusions mentioned in the above are the contributions of this thesis to knowledge base of this field.