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.

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Metal-organic frameworks (MOFs) are a new class of porous materials composed of a three-dimensional network of metal ions held in place by multidentate organic molecules. MIL-100(Fe) (molecular formula: Fe3O(H2O)2OH(BTC)2), as one kind of MOFs, has an excellent performance of water sorption due to the large specific surface areas and high porosity. The paper proposes an innovative application of MIL-100(Fe) as a new kind of moisture buffer material to control the indoor humidity passively. MOFs can moderate indoor moisture fluctuation, which will greatly reduce the energy consumption of HVAC systems and improve the building energy efficiency. In the paper, microstructure and moisture characterizations of MIL-100(Fe) have been carried out. The moisture buffer value (MBV) of MIL-100(Fe) has been measured and compared to the typical building materials. The results show that MIL-100(Fe) can absorb up to 15 g•m -2 •RH -1 at 8 hours, which is 33 times higher than the laminated wood. A novel lumped model for building latent load simulation has been developed. The energy saving potential by using MOFs in a typical office in different climates was calculated. The results show that a 5 m 2 MOF wall panel can remove most of the latent load in dry and moderate climates without any energy input; MOFs can be regenerated by night ventilation. In the hot and humid climate, the MOF materials can remove 73.4% of the latent load, and can be easily regenerated by using low-grade energy.

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