| The supply diffuser influences air flow patterns in the space with the heating, ventilating and air-conditioning (HVAC) system. How to accurately quantify its impact is essential for the proper design of air distribution systems. Some simplified CFD (Computational Fluid Dynamics) modeling methods are available. Among them, the box and momentum methods are the most popularly used. Different from the mixing system, the underfloor air distribution (UFAD) system employs the supply diffuser in the occupied zone and takes advantage of room air stratification for thermal comfort and energy saving. The design of this system is more sophisticated but requires practical tools, and the objective of this thesis is to develop such tools based on the supply diffuser simulation and air temperature stratification models.; The box method cannot be employed where the buoyancy force dominates indoor air flow, as is the case with the UFAD system. In this thesis, the fully represented geometry method (FRGM) was proposed to model the supply diffuser. The aim is to reveal the influence of diffuser configurations on the air flow pattern near the supply diffuser. This method was validated with the experimental data from a precombustion chamber. Employing the standard kappa - epsilon turbulence model, the FRGM presented more accurate results near the supply diffuser than the momentum method. With this method, the need to measure the input conditions near the supply diffuser can potentially be eliminated, which is difficult and inaccurate to do due to the large gradients. The RNG kappa - epsilon turbulence model was also investigated with this method and it was found more suitable for predicting flow patterns in the downstream recirculation zone.; With the FRGM, two supply diffusers, named the swirling and square diffusers, were employed in UFAD systems for different thermal environment investigations. It was found that indoor air temperature stratification can be maintained with both supply diffusers, but the thermal environment in the occupied zone was greatly influenced by the configuration of the supply diffuser. The swirling diffuser generated a more uniform thermal environment than the square diffuser due to the 'swirling' characteristic. Furthermore, the effects of the vane declining angles of the swirling diffuser were investigated, and it was found that two different flow patterns can be created, the horizontal and vertical flows. The horizontal flow is preferable for better thermal comfort. (Abstract shortened by UMI.)... |
