Water Transmission Mechanisms in Advanced Ionic Membranes for HVAC Applications.

Ionic membranes are widely used in the electrochemical applications such as electrolysis and fuel cells. Recent advances in these membranes have led to new markets for ionic membranes, that can provide high water permeability in heating, ventilation, and air conditioning (HVAC) applications. These materials can be useful in many applications to help provide more efficient building technologies and higher indoor air quality through devices such as ionic liquid heat pumps (ILHPs), ionic liquid desiccants (ILDs), and energy recovery ventilators (ERVs) and water-based evaporators (WBEs). Water transmission mechanisms behind the water transport is not well understood, since different functional membranes provide transmission in different ways. Water transportation can be a function of ionomer structure via the building blocks of the backbone, or from the functional groups on the side chains or from subtle features in membrane design and composition. In this work, we studied the permeation properties of different advanced ionic membranes. Membranes that show high water selectivity, and permeances exceeding 4x10 5 g/(day*m^2*Pa) are presented. Principal mechanisms driving the water transmission such as sorption, diffusion, and pervaporation (permeation/evaporation) are described and identified for different classes of membranes. High performance membranes are identified for optimum applications for different HVAC systems.