Metal-Organic Frameworks as advanced moisture sorbents for energy-efficient high temperature cooling

Abstract

Latent cooling load accounts for 30% of the total load of air-conditioning, and its proportion is even higher in many tropical and subtropical climates. Traditional vapour-compression air-conditioning (VCAC) has a low coefficient of performance (COP) due to the refrigeration dehumidification process, which often makes necessary a great deal of subsequent re-heating. Technologies using conventional desiccants or sorbents for indoor moisture control are even less competitive than VCAC due to their high regeneration temperature, long cycling time and bulky components. Here, we report a novel high temperature cooling system that uses porous metal-organic frameworks (MOFs) as advanced sorbents for humidity control. We directly coat MOFs on the surface of evaporator and condenser. The system has no additional components compared to a traditional VCAC. The evaporator can simultaneously remove both the sensible and latent loads of the incoming air without reducing the temperature below its dew point. The regeneration of wet MOFs is completely driven by the residual heat from the condenser. The MOF-coated heat exchangers can achieve a cooling power density of 82 W·L−1. We demonstrate that the system has a high COP, up to 7.9, and can save 36.1% of the energy required, compared to the traditional VCAC system with reheating. The amphiphilic MOFs used in the research have high water uptake, are made of low-cost raw materials and have high hydrothermal stability. They thus have the potential for being scaled up for large-scale applications in air conditioning.

Kinetic stability of metal–organic frameworks for corrosive and coordinating gas capture

“…The stability of MOFs towards water has been extensively investigated [58][59][60]82 because it is the most common coordinating and corrosive gas present in the atmosphere as well as in many applications like postcombustion gas streams, 6,83 gas sensing, 84 or in fuel cells requiring proton conducting materials. 85 Additionally, the capture of water vapor has several desirable applications including dehumidification, 73,86,87 heat transfer, 88,89 and atmospheric water capture. 41,[90][91][92][93][94] These applications all rely on cycles in which water alternatively fills the pores, and then is desorbed, creating a requirement for extensive cycling stability.…”

“…121 Additionally, Fe3O(OH)(BTC)2 (Fe-MIL-100) was investigated for latent cooling load reduction dehumidifying climate control air streams, and a MOF coating on a heat exchanger could be cycled 2000 times, while losing only 4.5% of the original capacity. 86 Carboxylate MOFs employing transition metals later or lower-valent than Fe 3+ are not candidates for water sorption applications due to stability concerns. Figure 4: Water Capacities of Porous Solids.…”

Water Vapor Adsorption–Desorption Behavior of Surfactant-Coated Starch Particles for Commercial Energy Wheels

“…12,17,18 Also, hybrid substrates such as synthesized silica gel-composite materials 19−21 and metal–organic frameworks (MOFs) have been reported. 22−26 Research on alternative desiccants such as starch, wheat, cassava, corn grit, and durian peel suggest that agriculture-based biomass possess unique water adsorption–desorption capabilities with additional benefits of low cost, high abundance, and sustainable nature. 27−29 Recently, Fathieh et al 30,31 conducted a sorption study on high amylose starch (HAS 15 ) using the component testing of an energy wheel, where the performance of HAS 15 and mesopouros silica gels (SG 13 ) with variable particle sizes were compared (commercial solid desiccants).…”

A close view of the organic linker in a MOF: structural insights from a combined 1H NMR relaxometry and computational investigation

“…Over the last two decades, metal organic frameworks (MOFs), also known as coordination polymers, have aroused increasing interest because of their high potential for applications in diverse fields, such as gas separation and storage, 1,2 energy storage, 3 catalysis, 4 and thermal energy conversion. [5][6][7] These hybrid crystalline solids are made of metal clusters linked by organic multidentate ligands that form extended three-dimensional porous frameworks with tunable pore size and shape through suitable chemical functionalities. Distinctive features of these versatile materials are extraordinarily large porosity and surface area, and unique adsorption properties.…”