Solar Air Conditioning with Metal Organic Frameworks
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Date
2020-05
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The Ohio State University
Abstract
Air conditioning is responsible for 5% of energy consumption in the United States as is increasingly in demand across the world as the global middle class continues to grow in size. During hotter months, electricity used to power cooling systems becomes taxing on electric grids, constituting approximately 40% of peak power demand. Traditional air conditioning (AC) systems are also associated with harmful environmental impacts. Both refrigerants used for cooling and fossil fuels used in power contribute to global warming by acting as green-house gases (GHG). Due to the negative effects associated with emissions, the ultimate goal of this research is to drastically reduce non-renewable energy consumption associated with AC units. Generations of technologies have been developed to address this ongoing issue. An emerging solution involves the integration of metal-organic frameworks (MOFs) sorbents into a solar air conditioning system. Because of MOF properties, this integration allows for a thermally driven cycle without requiring a non-renewable energy input.
This thesis is comprised of six chapters geared towards assisting in the determination of the most efficient and effective means of incorporation of MOFs into AC systems. Primarily by conducting an extensive literature review, the third chapter discusses Metal Organic Frameworks in depth for determining the most suitable candidates for this research project. Specific needs for the system are examined with different MOFs that meet the criteria considered. In chapter four, feasibility of integrating MOFs into a membrane through sorption measurements is tested for candidate MOF CAU-10. Chapter five is centered around modeling a MOF-assisted indirect evaporative cooler using EES: Engineering Equation Solver. Modeling outputs give a preliminary understanding of the cooling process and its effect on temperature.
Together, these chapters move toward showing the feasibility of operation and its applicability to the field of renewable AC. The study of MOF attributes in Chapter 3 focused on Relative Humidity (RH) at which the MOFs demonstrated a steep water uptake, water adsorption capacity, temperatures for MOF regeneration, long term stability, and cost to synthesize and fabricate. These investigations showed Co2Cl2(BTDD), MIL-101, MIL-100(M), MOF-841, and CAU-10 to be the most promising applicants. Through sorption measurements of MOF material CAU-10 its isotherm demonstrated a capacity at the adsorption step below 0.30 gH2O/gMOF but a maximum capacity over 0.5 gH2O/gMOF. The EES model results showed 80-90% of recycled air provides a supply temperature necessary for indoor cooling below 21 oC. Chapter six summarizes all results and gives recommendations focused on thermodynamic optimization.
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Keywords
Solar, Metal Organic Frameworks, Air Conditioning, Energy, Sorption, EES, Green House Gases, Water Adsorption