(415f) Hollow Fiber-Based Membranes for Water Vapor Recovery – Materials to Module & Prototype

It is almost 99 years since Willis Carrier introduced the first refrigeration compression-based air conditioning that made the indoor environment more comfortable. The demand for air conditioning is still booming, with a market of 5.5 billion units by the end of 2050. Around 40% of world energy in commercial and residential buildings is consumed by heating, ventilation, and air-conditioning units (HVAC), and more than 75% in the Kingdom of Saudi Arabia. Simultaneously about 10% of greenhouse gases released to the environment are by cooling units. As the impact of global warming increased steadily, demand for energy-efficient and environmentally friendly dehumidification units for air conditioning escalated; after all, it is the dominant energy-consuming segment in HVAC units. At present, dehumidification is based on vapor condensation and desiccant-based absorption, which increases overall capital and maintenance costs, the need for ample spaces, and, not the least, high energy utilization of up to 55% of the energy supplied to HVAC units. The available technologies offer a coefficient of performance (COP): the ratio of latent heat removed to pump energy supplied of 0.5 to 0.9. Membrane-based dehumidification is portrayed as a substitute due to its lower footprint and miniaturized prototype dimension, primarily when hollow fibers are employed.

In our research, we have developed a polyetherimide (ULTEM) hollow fiber using our in-house pilot-scale spinning machine. These support fibers were coated with different active layers proving high water vapor transport capability to the fibers. Some of the examples for the active layers prepared are Sulfonated Penta block copolymer (NEXAR), eco-friendly amino acid-based ionic liquid encapsulated in carbon capsules (ENIL), and naturally abundant polyphenols. Each unique material has its characteristics and helps to transport water vapor from the shell to the lumen side at a higher rate with the help of smaller vacuum pressure of up to »650 mbar saving energy. The materials have shown water vapor permeance between »4800 GPU to 13,000 GPU with a selectivity of »133 to 47300. The range of permeance and selectivity helps their applicability not only in HVAC units but also for a specialized application like natural gas dehydration, where high selectivity of membranes is necessary.

As a dehumidification unit for an HVAC system with 500 CFM of humid inlet air with 80-90% humidity at 33.5°C, about »6 m² of membrane area is needed. An in-house ROTA-Me centrifuge prepared the modules »30 cm long and »6 cm in diameter, carrying »500-700 fibers. The hollow fiber configuration with the advantage of miniaturization with higher packing density would give the final unit dimension of 0.28m x 0.2m x 0.2m, which is relatively small and portable. The Modules were tested in natural conditions for more than 380 days continuously. They showed a decline of » 7% in water vapor transport with COP of 2.45. The proposed material and prototype have vast potential in dehumidification for air conditioning and domestic and industrial dehydration process, offering a sustainable solution and benefits for the community.