Evaluation of Membrane-Based Dehumidification Systems: Pressure Permeance of Dry Air in Commercial and Composite Membranes

Air conditioning typically accounts for 40% to 50% of a building's energy consumption, making it a significant target for energy efficiency improvements. As a result, reducing the energy use of air conditioning systems has emerged as a critical challenge in the built environment. In response, researchers have recently focused on developing advanced technologies that enable independent control of temperature and humidity, which are essential for enhancing occupant comfort and improving indoor air quality. Among these innovations, membrane-based dehumidification has attracted considerable attention for its potential to provide passive, energy-efficient moisture control. An effective dehumidification membrane should possess low permeance to dry air and high permeance to water vapor, allowing selective mass transfer. Measuring dry-air permeance is essential for evaluating the membrane's gas-separation capability and predicting its performance in practical systems. If dry air permeance is too high, excessive air from the supply side may leak to the permeate side, reducing airflow delivery and increasing operational demands. To offset this, more supply air would be needed, increasing fan power, equipment sizing, and energy consumption. This study evaluated the pressure permeance of commercial Nafion 212, Nafion 117, and a custom-made Carboxyl PI composite membrane under controlled vacuum recovery conditions. The findings indicated that the pressure recovery rates followed the order Nafion 212 > Nafion 117 > Carboxyl PI, with all membranes exhibiting acceptable gas barrier performance. These results support the application of composite membranes in energy-efficient Heating, Ventilation, and Air Conditioning (HVAC) systems and highlight the importance of dry air barrier properties in membrane design. Furthermore, the results suggest that excessive dry-air permeance may increase the risk of airflow crossover in practical HVAC applications, potentially raising auxiliary fan power demand. Therefore, membrane gas-barrier performance is not only a material property but also a critical parameter influencing overall HVAC energy efficiency.