Abstract

Energy and indoor air quality concerns have motivated extensive research on air infiltration and ventilation in buildings. Airflow models have been developed to study the problem and to assist in the building design process. Existing research concentrates on measurements, modelling and predictions of steady-state airflow caused by wind-induced pressures, thermal buoyancy and mechanical ventilation systems. Wind-induced pressures on building envelopes have temporal variations due mainly to the wind gustiness. The resultant airflow has both mean and fluctuating components. Existing research shows discrepancies between the current steady-state airflow predictions and the actual air exchanges influenced by fluctuations. This thesis is devoted to the development of a comprehensive framework and methodology for airflow analysis and design assistance for buildings under both mean and fluctuating driving forces. A building airflow system is seen as two subsystems: steady-state and fluctuating. In the fluctuating airflow system, the temporal variations in wind pressures are taken as driving forces. The predictions of the resultants fluctuating airflow and internal pressures are based on the statistical linearization of flow relations, proper considerations of large openings, the system theoretic approach to governing equation formulations, and, frequency and spectral analyses for solutions. By combining both fluctuating and mean airflow solutions, the total air exchange in a building is obtained. Three types of validation strategies are employed. Numerical simulations are carried out to evaluate the effects of the statistical linearization on solutions. Laboratory experiments are designed, implemented and conducted to validate the fundamental relations. The theoretical predications are also compared to field experimental data. The fluctuating airflow model provides correct predictions for the simulation conditions and the experimental setups. In addition, modelling and sensitivity analysis procedures for steady-state airflow systems using a system theoretic approach are developed to calculate the influences on airflow results of the variations in building and climatic conditions, and to facilitate error analysis and building ventilation designs. Future research directions include: the incorporation into the existing research paradigm of the developed sensitivity analysis procedure and fluctuating airflow model, and the acquisition of more suitable data on characteristics of fluctuating driving forces.