The concept of a humidity pump is inspired by a heat pump. A humidity pump is a device that can transport moisture through the inverse gradient of vapor concentration, i.e., the vapor can be transferred from a relatively low-humidity space to a high-humidity space. For example, in summers, the humidity pump will transfer moisture from cool and less-humid indoor condition to a hot and humid outdoor condition; vice versa, in winters.
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 moisture control technologies, for example, 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 (e.g. silica gel, zeolite etc.) for indoor moisture control are even less competitive than VCAC due to their high regeneration temperature, long cycling time and bulky components.
Desiccants play an important role in the humidity pump. Traditional desiccants such as silica gel and zeolites possess low adsorption capacity and poor regeneration ability and this limits the development of the adsorption dehumidification system. Though a composite desiccant (silica gel-based, carbon-based, etc.) has been prepared by impregnating hygroscopic salt to enhance the adsorption capacity, hygroscopic salts are unstable and deliquesce easily under high humidity. Metal-organic framework (MOF) is a new type of porous crystalline material formed by self-assembly of inorganic metal ions and organic ligands. MOFs possess many good properties like huge internal surface area, large micropore volume, physicochemical and chemical variability as well as low regeneration temperature. Although traditional inorganic porous desiccant has been investigated for a humidity pump, the application of MOFs in humidity pump is still worth investigating owing to its high potential in moisture transfer.
In the present study, a humidity pump based on MOFs is fabricated, and its working principle and operation mode are introduced. The performance and impact factors of the device have also been investigated by experiments under different conditions. The localized moisture control ability of the device has been tested experimentally, which provides an important insight to precise moisture control in a confined space.
More on this project
P. Hou, K Zu, M. QIN*, S. Cui, A novel metal-organic frameworks based humidity pump for indoor moisture control, Building and Environment, 107396, 2020