ECO-CBET: GOALI: Condensing water from the air for building dehumidification and decarbonization using thermo-responsive desiccants

University Of Texas At Dallas, Richardson TX

Investigators

Abstract

2318720 (Shuang). Managing the humidity of buildings is essential for maintaining occupant comfort, reducing defects in moisture-sensitive manufacturing (e.g., semiconductors), and preventing foodborne pathogens in food preservation. Existing Heating, Ventilation, and Air-conditioning (HVAC) systems rely on either cold surface condensation or hygroscopic materials as desiccants to remove moisture from air. However, this is an energy-inefficient process due to the low-temperature setpoint essential for sufficient moisture condensation and the extra energy required to overcome significant enthalpy of vaporization in dehumidification. Currently, humidity control in buildings alone is responsible for 600 million tons of CO2 annually. Hence, efficient air dehumidification represents an excellent opportunity to reduce energy use and greenhouse gas emissions to facilitate the sustainability and decarbonization movement and counteract climate change. The vision of this convergent project is to initiate and establish high-efficiency dehumidification systems that directly condense water from the air through collaborative and interdisciplinary efforts in building sustainability, thermal transport, civil engineering, and chemical engineering. This fundamental research promoting more efficient building dehumidification will directly benefit national health and national manufacturing. Furthermore, the research is closely integrated with interdisciplinary environmental research training for college students and early-career scientists, which will benefit the STEM workforce. This project pursues energy-efficient dehumidification utilizing Thermo-Responsive (TR) desiccants with temperature-dependent adsorption isotherms—benefiting from the thermo-responsive switchable hydrophilicity below and above the Lower Critical Solution Temperature (LCST)—and high adsorption capacity. In addition, the thermo-responsiveness of TR desiccants breaks traditional desiccants’ fixed affinity to water, which allows for the release of water in liquid form and avoids the high energy requirements of water vaporization in traditional desiccants during the regeneration. The project will (1) develop durable TR desiccants with tunable LCSTs and optimum temperature-dependent adsorption isotherms for different dehumidification conditions, (2) improve the heat and mass transfer rate of TR desiccant wheels by optimizing the design parameters through modeling and experimental validation, (3) develop techniques to remove the adsorbed water in liquid form, and (4) evaluate the efficiency of the TR desiccant wheel in the dehumidification system by performing a hardware-in-the-loop (HIL) experiment. The proposed TR desiccant wheel with temperature-dependent adsorption isotherms leads to low regeneration temperatures and the potential to bypass the heat of evaporation. The unique property of desorbing the adsorbed moisture in the liquid form during the regeneration saves up to 6x energy compared to traditional approaches in HVAC application, which saves up to 30% carbon emission. Moreover, condensed water from the air can be collected and used to alleviate water scarcity in building operations in arid climates. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.