<p>In the current marketplace, most ducted split-system heat pumps feature single-speed compressors and fans. To meet forthcoming minimum energy rating requirements, reduce operational costs, and increase environmental sustainability, the seasonal heating and cooling efficiencies of heat pump systems must be improved. Variable-speed equipment offers significant advantages for load modulation and has the ability to increase the seasonal performance greatly. Additionally, novel electrical motor technologies, such as permanent magnet (PM) motors, can reduce the power consumption of the motors by up to 25-55% compared to the widely used permanent split capacitor (PSC) motor or electronically commutated motor (ECM). In this study, a low cost ducted single-speed heat pump system with a cooling capacity of 10.55 kW was analyzed to quantify the impact of fan and compressor motor efficiency on seasonal coefficient of performance (SCOP). Furthermore, single-speed components were replaced with variable to evaluate the performance increase. The single-speed heat pump was experimentally tested, and the results were used to tune a detailed model for further performance analyses. The efficiency was evaluated in heating and cooling mode according to AHRI Standard 210/240 and with an energy savings and cost analysis, that details the SCOP and costs for different locations. The conversion of the fan motors to high efficiency PM magnet motors increased the SCOP by up to 6%. The impact was dependent on the initial motor efficiency and the operational mode. The indoor unit fan motor has a large impact on SCOP in cooling mode and a low impact in heating mode because of the motor waste heat’s impact on capacity. The conversion to a fully variablespeed system greatly increased the performance, with a 72% increase in cooling SCOP and a 19% increase in heating SCOP. The energy savings and cost analysis concluded that the fan motor conversion from single-speed to high efficiency motors is economically viable, but the financial benefit of the upgrade to variable-speed depends on the intended location of use.  </p>

An air‐cycle air conditioning system, using a typical automotive turbocharger as the core of the system, was designed and tested. Effects on engine performance were kept to a minimum while providing the maximum amount of cooling possible and minimizing weight and space requirements. A test stand utilizing shop compressed air was developed to measure component performance. An unmodified automotive turbocharger was tested initially as a baseline in a Reversed‐Brayton Cycle air cooling system. Once the baseline was established, another aircycle machine, assembled from commercial turbocharger components chosen individually to optimize their performance for cooling purposes, was tested to improve the overall cycle efficiency. Finally, once the air‐cycle air conditioning system was optimized, it was tested on an engine to simulate more realistic operating conditions and performance. The shop‐air test stand experiments showed a peak dry‐air‐rated (DAR) coefficient of performance (COP) of 0.38 and a DAR cooling capacity of 0.45 tons for the baseline turbocharger, and a peak DAR COP of 0.73 and DAR cooling capacity of 1.5 tons for the optimized system with a modified turbocharger. The on‐engine testing was limited due to a thrust bearing failure in the ACM. However, the data collected at lower engine load and speed indicates a DAR COP of 0.56 and a DAR cooling capacity of 0.72 tons. On‐engine testing was planned to include operating points where the stock turbocharger was utilizing turbine‐bypass to limit boost pressure. While it wasn't possible to continue testing, it is expected that DAR COP and cooling capacity would have increased at higher engine load and speed, where turbine‐bypass operation typically occurs.

<p>Air conditioning, space heating, and refrigeration account for approximately 40% of the electricity usage in the U.S. residential and commercial building sector. To improve energy utilization and reduce energy consumption in space conditioning applications, advanced heat pumping technologies are needed. The chemical looping heat pump (CLHP) is a promising thermodynamic cycle that has shown the potential to achieve a cooling coefficient of performance (COP_c) increase of over 20% relative to conventional vapor compression (VC) systems.</p> <p><br></p> <p>The overarching goal of this study is to evaluate the chemical looping heat pump concept for residential applications, including thermodynamic potential, as well as technical and economic feasibility before developing and deploying a pilot scale system. The evaluation process includes advanced thermodynamic modeling for better assessments of working fluids and systems, techno-economic analysis for initial cost assessment of the scaled-up system, and small-scale experiments for proof-of-concept.</p> <p><br></p> <p>A working fluid screening process was developed to identify suitable working substance pairs for CLHP systems. The key metrics for evaluating the working fluids are associated with the possibility of phase change after a chemical reaction, reversible cell potential and power consumption, and cooling capacity of the system. Such metrics were applied to several fluids to assess their suitability. It was found that isopropanol/acetone working substances showed the highest cooling capability for a given power consumption. Even though this approach was applied to particular organic fluids (e.g., alcohols and ketones), this analysis can be generalized to other single-component fluids, multi-component fluids, and several chemical designs.</p> <p><br></p> <p>A modeling framework to estimate operating cost, capital cost, and levelized cost of energy was developed to enable a direct early-stage comparison of a CLHP with conventional VC systems. The models were helpful in understanding the influence of key factors such as efficiency, unit utilization (annual cooling and heating delivered, kWh_t/yr), and price of electricity ($/kWh_e) with the goal of determining target markets for initial CLHP products. The LCOE of CLHP could be less than that of VC in the case of high utilization (≥  20,000 kWh_t) with high performance improvements (COP_CLHP/COP_VC = 1.3) even though the capital cost of the CLHP is nearly 1.5-2 times higher than VC.</p> <p><br></p> <p>The key process of a CLHP cycle, which is electrochemically driven phase transformation, was experimentally demonstrated based on the advanced test rig and electrochemical cell. A polymer electrolyte membrane flow cell with a self-fabricated membrane electrode assembly and flow channels was employed to drive the reaction. The breakdown voltage analysis indicates that ohmic and mass transfer overpotentials account for more than 90% irreversibilities of the reactions. In addition, the results showed the possibility of phase transition of 20-30% at current density of ~0.003 A/cm² and the cell voltage of 0.025 V. The extent of a chemical reaction can be further improved by increasing the current and reducing the flow rate.</p> <p><br></p> <p>A semi-empirical cycle model was leveraged to predict realistic system performance. The model includes an electrochemical cell model with other component models in a CLHP cycle. The Second law efficiency was 50% of the Carnot limit with a cooling capacity of 2.24 mW (cooling density of 1.6 W/m²) at sink temperature of 40 °C  and source temperature of 23 °C. The cause for the precipitous drop in COP_c with increasing current density was overpotential, which requires further research on the optimization of membrane and catalytic materials as well as a geometry of flow channels to minimize the losses. Higher efficiency can theoretically be achieved at an elevated fluid temperature as long as an electrochemical cell can achieve a greater degree of conversion.</p> <p><br></p> <p>There are several challenges that should be reconciled in a future operational device and cycle at scale. Additional research on both material- and system-level performance is indispensable to meet practical size requirements. Nevertheless, this study is intriguing in terms of the possibility of developing a high efficiency device with the ability to use more environmentally friendly working fluids. Broadly, this CLHP research can contribute to accelerating the development of the newly emerging field, which is thermal systems coupled with electrochemical processes, that can maximize system efficiency using low-GWP fluids.</p>

<p dir="ltr">Building cooling and ventilation account for nearly 10% of the global electricity consumption. In fact, a recent study even showed that, globally, dehumidification consumes more energy than sensible cooling. One high-efficiency dehumidification technology is selective membrane dehumidification. Selective membranes allow water vapor transport but block air transport. There are two overarching gaps in the literature that are addressed in this dissertation: (1) vacuum membrane dehumidification (VMD) has been rigidly defined as an isothermal process and (2) literature on one of the most efficient VMD system designs, which I will refer to as the “dual module humidity pump,” is limited to ideal thermodynamic modeling (no experimental demonstration or practical system modeling in the current literature).</p><p dir="ltr">This work presents a novel system concept, referred to as the “Active Membrane Energy Exchanger” (AMX), which specifically couples VMD and air cooling into one process to provide the first non-isothermal VMD system concept. The present study provides a wholistic understanding of the benefits and limitations of the AMX approach through both thermodynamic system modeling and experimental protype development and demonstration.</p><p dir="ltr">System models developed in Engineering Equation Solver were used to compare the energy performance of the AMX to other HVAC technologies. These models showed that the AMX could achieve up to 25% annual cooling electricity savings in commercial buildings and up to 60% annual cooling electricity savings in 100% outdoor air applications. Experiments showed that combining cooling and dehumidification increased membrane permeance by up to 40% and increased dehumidification performance by 3-6%. Further demonstration showed the prototype could remove up to 45% of the humidity in the humid air flow but struggled to reject all of that vapor to the exhaust air (mass transfer imbalance). This discovery enabled a practical thermofluid model to estimate theoretical and practical COP limits, which were approximately 40 and 10, respectively. Additionally, a global sensitivity analysis on the new model showed that mechanical design is far more limiting to the performance than material design.</p><p dir="ltr">In summary, this dissertation develops and demonstrates a novel air conditioning technology, from system modeling to prototype demonstration. This work was funded and guided by industry partners, and the results of this dissertation are a major step towards real-world implementation.</p>

No description available.

This paper examine a passive cooling system for a humid climate. This system will be divided into two parts, a radiative system and an evaporative system combined into a roof pond system. Performance of the radiative system will be enhanced through the use of a selective cover which will make use of an atmospheric window between 8 and 13um. An attempt will also be made to thermally isolate the radiative system from convective gains with the evaporative system. The evaporative system will consist of a water, solvent and dye layer over the selective cover of the radiative system. The performance of the evaporative system will be enhanced by virtue of the increased vapor pressure made available through the use of solvents. The main solvent to be examined shall be methanol. The increased vapor pressure shall sufficiently increase the rate of evaporative cooling to a point where useful cooling is obtained even under high humidity conditions. It was found that a solution with a 0.8 mole fraction of methanol in the evaporative system could cool a sufficiently large water storage to 45°F using a 300 m2 roof pond. This is a heat sink which if used to provide cooling and dehumidification, will provide 576000BTU of cooling. This is the equivalent of a 3 ton unit operating 16 hours a day. It was found that a water layer thicker than 0.1 mm would radiatively isolate the selective cover, making the concept of a liquid thermal protection useless as a means of providing only convective protection. However, as a selective cover, teflon was found to make the best use of the 1-13um window. As a result, this would provide 33 BTU/ft2-might as compared to 11 BTU/ft2-night for a black cover. It was also found that a green of blue and yellow or red dye mixture, when dissolved in water, would provide a black surface throughout the visual and infrared range.

2023 / The increasing incidence and intensity of days and spells of extreme heat is expected to continue with climate change, with interconnected and cascading consequences across multiple scales and sectors. In particular, high temperature exposures directly affect population health (e.g., increased risk of hospitalization and death) and cooling energy demand (i.e., the use of residential air conditioning (AC) as adaptation). Heat extremes are often amplified in urban areas due to the thermodynamic properties of the built environment. While we have a strong understanding of the relationship between heat and energy demand, energy and AC, and the impacts of heat on morbidity and mortality, there remain notable knowledge gaps in the dynamics that underpin these relationships, and only a handful of studies are able to explore their linkages together, especially at fine spatial scales. In this dissertation, I combine econometric and epidemiological methods to provide further insights into several dimensions of the intersection of heat, electricity, AC, and health in urban populations, and holistically assess these linked relationships together. In my first chapter, I characterize the response of urban electricity demand to temperature at fine temporal resolution across a subset of world cities, and quantify the impacts of future heat adaptation on net and peak energy demand under mid-century warming. Temperature-demand response functions and future demand impacts are heterogeneous across temperate and tropical cities, highlighting the important role that the structure of electricity demand plays alongside distributional temperature shifts in evaluating the impacts of climate change on future energy demand. In my second chapter, I construct fine spatial resolution estimates of any residential AC across a large set of US metropolitan areas. Inter-urban availability of AC exhibits a strong latitudinal gradient, while intra-urban AC is systematically unequally distributed within cities. This inequality is also negatively correlated with social vulnerability (SVI) and surface urban heat island intensity (SUHI), suggesting that differential AC compounds existing heat health disparities. In my third chapter, I additionally compute individual and ZCTA-level estimates of AC use on extreme heat days alongside individual probability of AC in California cities, and evaluate the differences in the moderating effects of these related attributes of heat vulnerability on heat-related hospital admissions. AC prevalence and AC use are correlated, but both measures of adaptation are only weakly correlated with social vulnerability within cities. The spatial distribution of health risks from extreme heat echoes spatial patterns of increasing social vulnerability, and both AC prevalence and use significantly modify the association between extreme heat and a number of health outcomes. However, effect estimates differ between AC prevalence and AC use, suggesting that AC ownership does not necessarily reflect AC usage, and, crucially, that there remain additional unobserved dynamics driving the heat-adaptation-health relationship. Identifying the underlying factors and determinants of population heat health vulnerability at the local scales in which impacts and adaptation decisions take place is necessary as cities and municipalities develop and refine heat resilience policies and climate adaptation strategies aimed at reducing heat health inequities and improving community well-being.

<p dir="ltr">Dehumidification is pivotal in contemporary society, especially for electronics and buildings. Electronic devices face operational risks due to moisture-related failures, with substantial economic impacts estimated between $0.5 and $5 billion annually from electrostatic discharge (ESD) alone. Around 20% of building electricity consumption is cooling-related, of which more than 50% is usually latent load (removing water in the air). Innovative water vapor-selective membranes offer a distinctive solution for managing latent loads, as the ideal energy requirement for separating water vapor with a membrane is much smaller than the energy required for condensing it out of the air. Vacuum membrane dehumidification (VMD) is a promising alternative dehumidification technology for its quick operation and excellent energy savings. It applies selective membranes that enable water vapor to pass but not air.</p><p dir="ltr">This work consists of investigating VMD systems in electronics and building dehumidification. Electronic devices, essential in modern society, face operational risks due to moisture-related failures, with substantial economic impacts estimated between $0.5 and $5 billion annually from electrostatic discharge (ESD) alone. Lack of relative humidity (RH) control is a leading cause of failure, with the critical RH threshold for clean electronic surfaces recognized at 60%. This study investigates Vacuum Membrane Dehumidification (VMD) as a novel dehumidification strategy, targeting the efficient control of RH within small electronic enclosures to mitigate moisture-induced failures. This work involves constructing a thermodynamic model for the VMD system, followed by the assembly of a physical prototype for empirical validation. The model integrates enclosure dimensions and membrane properties to simulate performance across various environmental conditions. Experimental validation of the model is conducted under controlled conditions to establish its accuracy. The results reveal that the VMD system achieves effective moisture removal with a Humidity Removal Fraction (HRF) of 30-65%, significantly influenced by the ambient RH and vacuum pressures. Energy optimization studies compare the VMD with conventional methods, illustrating superior performance in energy efficiency. The VMD system not only demonstrates its efficacy in RH management but also suggests a potential reduction in the operational energy requirements of electronic devices. This work establishes a foundation for membrane-based dehumidification technologies in electronic enclosure design, with broad applications across various sectors dependent on electronic systems.</p><p dir="ltr">The building dehumidification work is the first to integrate dual-module VMD with a residential vapor compression system, exploring recirculation air’s impact on energy consumption. Two membrane module designs (flat-sheet and hollow fiber membrane) are explored. A parametric study is conducted to assess the energy consumption of systems at different operation conditions. A practical way to size the membrane based on design conditions like AHRI 340/360 is introduced. Up to 17% of energy savings could be achieved in extremely humid weather conditions.</p>

Through the use of multiple-input/single-output (MISO) modeling, the propagation paths of sound within a reciprocating refrigeration compressor have been investigated and ranked. By investigating the nature of sound propagation within reciprocating compressors, it is hoped that compressor manufacturers can effectively formulate strategies for compressor sound reduction. From experimental data of compressor far-field sound output, suspension spring forces, and internal pressure fluctuations, a MISO model has been developed. From this model, the importance of the suspension system to the compressor far-field sound spectrum has been identified. In the frequency range above 800 Hz, forces passing through the suspension system appear to be the dominant contributor to shell excitation and sound radiation. Based upon this finding, it is recommended that modified suspension systems be considered as an avenue for compressor sound reduction efforts in the future. / Master of Science

published_or_final_version / Business Administration / Master / Master of Business Administration