Water Vapor Compression Technologies for Vacuum Membrane Dehumidification: Challenges, Requirements, and Future Directions

Vacuum membrane dehumidification (VMD) has emerged as a promising high-efficiency alternative to conventional condensation-based HVAC systems, offering the ability to decouple sensible and latent cooling loads. Despite its potential, practical implementation remains hindered, in part, by the lack of specialized water vapor compressors capable of operating under deep vacuum conditions. This study investigates the technical requirements and thermodynamic limitations of water vapor compression technologies specifically for VMD applications. Building latent loads were first simulated using EnergyPlus with a Department of Energy (DOE) reference large hotel building in a hot and humid climate (Miami, FL) to establish peak latent load design conditions. A thermodynamic model was then developed in Engineering Equation Solver (EES) to quantify the volumetric, thermal, and efficiency demands on the compressor across a range of operating conditions. Results indicate that even under favorable suction pressures (1,240 Pa), a single floor's latent load requires large-scale industrial compression hardware with a volumetric flow rate of 25.1 m3/min. At deeper vacuums (250 Pa), the required volumetric flow rate surges nearly fivefold, necessitating multiple parallel industrial units to serve just one floor. Furthermore, single-stage direct compression to atmospheric pressure leads to prohibitively high discharge temperatures (exceeding 780 degrees C) and low latent coefficients of performance (COPL < 1.0). In contrast, partial compression strategies, such as Sub-Atmospheric Condensation Systems (SACS) and Dual-Module Humidity Pumps (DMHP), maintain manageable discharge temperatures and high COPLvalues (exceeding 9.0 at a 70% isentropic efficiency). These findings demonstrate that while the development of dedicated vacuum compressor hardware remains a critical R&D need, low-pressure-ratio architectures currently offer the most viable pathway for energy-competitive VMD implementation in buildings.