Vacuum membrane-based air dehumidification (MAD) is potentially more efficient than refrigeration cycles. Air permeance through a membrane is inevitable, especially when there is a large pressure difference between the supply and permeate sides. Given the high specific gas volume under vacuum conditions, removing the permeating air from the dehumidifier is crucial for the stable operation of the vacuum compressor. Energy-efficient air removal techniques are still lacking, thereby hindering the development of MAD technology. This paper proposes a novel MAD approach using a vacuum mixing condenser. The cooling water directly condenses moisture from the vacuum compressor without any heat exchanger. The permeating air and water mixture in the condenser then experiences a quasi-isothermal pressurization process through a multiphase pump, enabling continuous dehumidification and air removal with low power consumption. The fundamentals of the proposed approach are illustrated, and mathematical models are built. Influences of air permeance rate, cooling water flow rate, condenser pressure, membrane area, and gravitational work are investigated. The results show that a COP of 8~12 is achievable to dehumidify air to 50%RH, 25 °C. The vacuum compressor consumes about 80% of the power. A low air permeance rate, low condenser pressure, large membrane area, and high gravitational work positively impact the COP, while the cooling water flow rate has a more complex effect. The proposed dehumidifier can use less selective membranes for higher permeability and cost-effectiveness.

Light-driven air dehumidification technology using photo-thermal materials capable of absorbing solar light to excite photo-induced drying process will be next-generation air dehumidification technology to implement near-zero carbon building air conditioning. To fulfil this goal, a bespoke natural light harvesting configuration to deliver high-intensity solar light radiation is promising. This research proposes a novel sun tracking, light concentration and transmission system for high-intensity solar light delivery. The system includes a dual-axis sun tracking unit coupled with a double-Fresnel lenses for sun tracking, light concentration and collimation to maximize solar light collection and a tubular light transmission system with a thoroughly assessed internal surface coating material, micro-silver, having excellent transmission efficiency throughout whole solar spectrum, especially infrared spectral region-a major spectrum for moist desorption. A numerical model was developed to characterize solar light transmission through the system; a prototype was constructed and installed on a mobile lab through roof and tested under real outdoor conditions. The experiment showed in the investigated incidence angle range of 53o-67o the transmission efficiency maintained 0.94–0.97 for straight section of tubular transmission system, but it decreased to 0.52–0.70 for a 90o curved section, identifying geometric curve as a major source of transmission loss; the light concentration achieves up to 2.83 times higher output light intensity. The model was validated by experimental data and a case study showed for monthly global horizontal irradiance of 150×103 -160×103 Wh/m2 in summer at Hull, the delivered solar energy exceeds 200 × 10³ Wh/m². The seasonal solar light delivery capability of the system is governed by both the solar irradiance and solar geometry.