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- Genre: Doctoral Dissertation
Description
Passive cooling techniques, specifically passive downdraft cooling (PDC), have proven to be a solution that can address issues associated with air conditioning (AC). Globally, over 100 buildings have integrated PDC in its different forms, most of which use direct evaporative cooling. Even though all surveyed buildings were energy efficient and cost-effective and most surveyed buildings were thermally comfortable, application of PDC remains limited. This study aims to advance performance of the single stage passive downdraft evaporative cooling tower (PDECT), and expand its applicability beyond the hot dry conditions where it is typically used, by designing and testing a multi-stage passive and hybrid downdraft cooling tower (PHDCT). Experimental evaluation on half-scale prototypes of these towers was conducted in Tempe, Arizona, during the hot dry and hot humid days of Summer, 2017. Ambient air dry-bulb temperatures ranged between 73.0°F with 82.9 percent coincident relative humidity, and 123.4°F with 7.8 percent coincident relative humidity. Cooling systems in both towers were operated simultaneously to evaluate performance under identical conditions.
Results indicated that the hybrid tower outperformed the single stage tower under all ambient conditions and that towers site water consumption was at least 2 times lower than source water required by electric powered AC. Under hot dry conditions, the single stage tower produced average temperature drops of 35°F (5°F higher than what was reported in the literature), average air velocities of 200 fpm, and average cooling capacities of 4 tons. Furthermore, the hybrid tower produced average temperature drops of 45°F (50°F in certain operation modes), average air velocities of 160 fpm, and average cooling capacities exceeding 4 tons. Under hot humid conditions, temperature drops from the single stage tower were limited to the ambient air wet-bulb temperatures whereas drops continued beyond the wet-bulb in the hybrid tower, resulting in 60 percent decline in the former’s cooling capacity while maintaining the capacity of the latter. The outcomes from this study will act as an incentive for designers to consider incorporating PDC into their designs as a viable replacement/supplement to AC; thus, reducing the impact of the built environment on the natural environment.
Results indicated that the hybrid tower outperformed the single stage tower under all ambient conditions and that towers site water consumption was at least 2 times lower than source water required by electric powered AC. Under hot dry conditions, the single stage tower produced average temperature drops of 35°F (5°F higher than what was reported in the literature), average air velocities of 200 fpm, and average cooling capacities of 4 tons. Furthermore, the hybrid tower produced average temperature drops of 45°F (50°F in certain operation modes), average air velocities of 160 fpm, and average cooling capacities exceeding 4 tons. Under hot humid conditions, temperature drops from the single stage tower were limited to the ambient air wet-bulb temperatures whereas drops continued beyond the wet-bulb in the hybrid tower, resulting in 60 percent decline in the former’s cooling capacity while maintaining the capacity of the latter. The outcomes from this study will act as an incentive for designers to consider incorporating PDC into their designs as a viable replacement/supplement to AC; thus, reducing the impact of the built environment on the natural environment.
ContributorsAl-Hassawi, Omar Dhia Sadulah (Author) / Bryan, Harvey (Thesis advisor) / Reddy, T Agami (Committee member) / Chalfoun, Nader (Committee member) / Arizona State University (Publisher)
Created2017
Description
The aim of this research study is to develop a passive architectural design morphology, tuned to the Sonoran Desert, which redefines Desert Modernism and integrates: (a) mitigation of heat transfer through the exterior envelope, and (b) use of daylight to inform appropriate architectural massing. The research investigation was delimited to mid-nineteenth century European modernist examples, and ends with mid-twentieth century modern architecture in the southwestern United States as viewed through the lens of environmental design. The specific focus was on Desert Modernism, a quasi-architectural movement, which purportedly had its beginnings in 1923 with the Coachella Valley, Popinoe Desert Cabin.
A mixed-method research strategy comprised of interpretive-historical research, virtual simulation/modeling analysis and logical argumentation is used. Succinct discussions on desert vernacular design, Modernism’s global propagation, and the International Style reinterpretations were illustrated to introduce the possibility of a relationship between Modernism and the vernacular. A directed examination of climatic responses included within examples of California Modernism, the Case Study Houses and Desert Modernism follows. Three case studies: a) the Frey House II, b) the Triad Apartments, and c) the Analemma House were assessed using virtual simulation and mathematical calculations, to provide conclusive results on the relevance of regionally tuned exterior envelope design and planning tactics for the Phoenix, Arizona area. Together, these findings suggest a correlation between environmental design principles, vernacular architecture, and Modernism.
A mixed-method research strategy comprised of interpretive-historical research, virtual simulation/modeling analysis and logical argumentation is used. Succinct discussions on desert vernacular design, Modernism’s global propagation, and the International Style reinterpretations were illustrated to introduce the possibility of a relationship between Modernism and the vernacular. A directed examination of climatic responses included within examples of California Modernism, the Case Study Houses and Desert Modernism follows. Three case studies: a) the Frey House II, b) the Triad Apartments, and c) the Analemma House were assessed using virtual simulation and mathematical calculations, to provide conclusive results on the relevance of regionally tuned exterior envelope design and planning tactics for the Phoenix, Arizona area. Together, these findings suggest a correlation between environmental design principles, vernacular architecture, and Modernism.
ContributorsSoltero, Ed (Author) / Zygas, Kestutis (Thesis advisor) / Bryan, Harvey (Thesis advisor) / Domin, Christopher (Committee member) / Arizona State University (Publisher)
Created2019
Description
A well-insulated dark conventional rooftop can be hotter than any other urban surface, including pavements. Since rooftops cover around 20 – 25% of most urban areas, their role in the urban heat island effect is significant. In general, buildings exchange heat with the surroundings in three ways: heat release from the cooling/heating system, air exchange associated with exfiltration and relief air, and heat transfer between the building envelope and surroundings. Several recent studies show that the building envelope generates more heat release into the environment than any other building component.Current advancements in material science have enabled the development of materials and coatings with very high solar reflectance and thermal emissivity, and that can alter their radiative properties based on surface temperature. This dissertation is an effort to quantify the impact of recent developments in such technologies on urban air. The current study addresses three specific unresolved topics: 1) the relative importance of rooftop solar reflectance and thermal emissivity, 2) the role of rooftop radiative properties in different climates, and 3) the impact of temperature-adaptive exterior materials/coatings on building energy savings and urban cooling. The findings from this study show that the use of rooftop materials with solar reflectance above 0.9 maintain the surface temperature below ambient air temperature most of the time, even when the materials have conventional thermal emissivity (0.9). This research has demonstrated that for hot cities, rooftops with high solar reflectance and thermal emittance maximize building energy savings and always cool the surrounding air. For moderate climate regions, high solar reflectance and low thermal emittance result in the greatest building energy cost savings. This combination of radiative properties cools the air during the daytime and warms it at night. Finally, this research found that temperature-adaptive materials could play a significant role in reducing utility costs for poorly insulated buildings, but that they heat the surrounding air in the winter, irrespective of the rooftop insulation.
Through the detailed analysis of building façade radiative properties, this dissertation offers climate-specific design guidance that can be used to simultaneously optimize energy costs while minimizing adverse warming of the surrounding environment.
ContributorsPrem Anand Jayaprabha, Jyothis Anand (Author) / Sailor, David (Thesis advisor) / Phelan, Patrick (Thesis advisor) / Huang, Huei-Ping (Committee member) / Wang, Liping (Committee member) / Yeom, Dongwoo Jason (Committee member) / Arizona State University (Publisher)
Created2022