Membrane module design, construction, and testing for vacuum sweep dehumidification (VSD): Part I, prototype development and module design

There is an unmet market demand for membrane-based humidity control air conditioning systems. This paper hypothesizes that this unmet demand results from the lack of optimized membrane module designs for this application. Designing membrane modules for vacuum sweep dehumidification (VSD) of building air requires the minimization of vacuum pump work and the maximization of the percent reduction in absolute humidity. Because the operating conditions for VSD differ significantly from the typical membrane gas separation process, the resulting membrane module design was significantly different than the typical hollow-fiber module. Theoretical and experimental analysis determined that the design should focus on reducing the feed/retentate boundary layer resistance to mass transport. The development process evaluated three module geometries. Testing and evaluation of the module geometries, using an industry standard feed humidity for designing air conditioning systems, showed that membrane module design can produce VSD membrane systems with better performance and energy efficiencies than standard cooling coil systems. The best module tested (patent pending) had an overall module water-vapor permeance of 4700 GPU for feed humidities of 11-g/kg; producing a 26% reduction in absolute humidity with < 2.5% product loss and requiring < 6.2 compression ratio for the vacuum pump.