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Doctoral Dissertation Final Defense

Ventilation plays an important role in promoting thermal comfort and Indoor Air Quality (IAQ). In conditioned space, ventilation can be operated and controlled through many means and methods, or so-called "ventilation strategies". Categorized by the placement of the terminal configurations and the control schemes such as supply temperature and velocity, each ventilation strategy has both advantages and disadvantages. The most common system called Mixing Jet Ventilation (MJV) has the advantage of its flexibility, but the performance is usually limited by neglecting the use of stratification. Unlike MJV, Displacement Ventilation (DV) fully utilizes stratified flow which is the key for enhancing removal of heat and pollutants. To maintain stratification, the supply velocity of DV must be low, and the supply temperature should be close to the room temperature. This limitation creates difficulties in control and operation. The challenge is to find a ventilation strategy where supply velocity and temperatures can be flexible, while maintaining the desired stratification. One system, called Impinging Jet Ventilation (IJV), potentially satisfies this challenge and, thus, deserves comprehensive studies. Using both full scale experiment and Computational Fluid Dynamics (CFD), IJV systems were modeled to examine different contributing variables to the success of this strategy. Among these variables, terminal configurations, cooling/heating scenarios, operation methods, and space volumes were given the first priority. Based on widely accepted standards, comprehensive indicators including ventilation effectiveness (VEF), ventilation performances, and Predicted Mean Vote-Predicted Percentage of Dissatisfaction (PMV-PPD) were applied. Validated CFD results reveal that IJV allows maximum velocity up to 2m/s (6.6f/s) and typical temperature of 13oC (55oF) to be supplied under cooling scenarios. Regardless of space size, peak performances can be achieved if the space under consideration is designed to be energy efficient. Using parameters discovered by this study, an advantage on energy conservation was found along with the thermal comfort and IAQ benefit. Energy reduction is made possible by high VEF reaching 1.1 allowing fresh air intakes to be reduced. Since these performances were confirmed by the results from a case study classroom, many architectural applications such as laboratories, passenger terminals, tunnels, atrium, etc., are possible candidates for IJV system.

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