Controlled environment agriculture allows the production of fresh food indoors from global locations and contexts where it would not otherwise be possible. Growers in extreme climates and urban areas produce food locally indoors, saving thousands of food import miles and capitalizing upon the demand for fresh, tasty, and nutritious food. However, the growing of food, both indoors and outdoors, consumes huge quantities of water - as much as 70-80% of global fresh water supplies. The utilization of liquid desiccants in a closed indoor agriculture cycle provides the possibility of capturing plant-transpired water vapor. The regeneration/desalination of these liquid desiccants offers the potential to recover fresh water for irrigation and also to re-concentrate the desiccants for continued dehumidification. Through the utilization of solar thermal energy, the process can be completed with a very small to zero grid-energy footprint. The primary research in this dissertation focused on two areas: the dehumidification of indoor environments utilizing liquid desiccants inside membrane contactors and the regeneration of these desiccants using membrane distillation. Triple-bore PVDF hollow fiber membranes yielded dehumidification permeance rates around 0.25-0.31 g m-2 h-1 Pa-1 in lab-scale trials. A vacuum membrane distillation unit utilizing PVDF fibers yielded a flux of 2.8-7.0 kg m-2 hr-1. When the membrane contactor dehumidification system was applied in a bench scale controlled environment agriculture setup, the relative humidity levels responded dynamically to both plant transpiration and dehumidification rates, reaching dynamic equilibrium levels during day and night cycles. In addition, recovered fresh water from distillation was successfully applied for irrigation of crops and concentrated desiccants were successfully reused for dehumidification. If applied in practice, the liquid desiccant system for controlled environment agriculture offers the potential to reduce water use in controlled environment agriculture by as much as ~99%.

<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>

Master of Science / Department of Mechanical and Nuclear Engineering / Steven J. Eckels / Membrane dehumidification and evaporative cooling applications have the potential to significantly improve the energy efficiency of air conditioning equipment. The use of wire mesh media in such membrane applications is feasible but has not been studied extensively. Therefore, the aim of this work is to investigate the heat and mass transfer performance of several different wire mesh media in membrane based dehumidification and evaporative cooling. There were six wire mesh membranes tested in an experimental facility. The wire mesh membranes vary with respect to percent open area, wire diameter, pore size and material. Two non-permeable, solid membranes were also tested in the facility and compared with the wire mesh membranes. The test section of the experimental facility consists of a narrow air duct and a plate apparatus. The membrane samples were fashioned into rectangular plates and installed into the test section. The plate membranes separate liquid water and air flow streams. The inlet air temperature and humidity are altered to produce condensation or evaporation at the membrane surface. The average convective heat and mass transfer coefficient of the air boundary layer is measured for each of the experimental plates. Membrane based dehumidification and evaporative cooling were accomplished using the wire mesh media. However, the wire mesh membranes did not exhibit any significant differences in their performance. The mesh plates were compared with the solid plate membranes and it was discovered that the solid plates exhibited significantly higher heat transfer coefficients during condensation conditions. This result most likely is due to the formation of large water droplets on the solid plates during condensation. The experimental data is then compared to analytical predictions of the heat and mass transfer coefficients developed from several heat transfer correlations and by invoking the heat and mass transfer analogy. The experimental data is also compared directly with the heat and mass transfer analogy. It was found that the data did not compare well with the heat and mass transfer analogy. This result is attributed to the fact that the membrane surface limits the amount of direct exposure to the gas-liquid interface.

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