Benefits of metal–organic frameworks sorbents for sorbent wheels used in air conditioning systems

Abstract

• Properly selected MOFs can absorb more moisture per cycle than silica gel. • MOFs can be regenerated at lower temperatures than commonly used sorbents. • MOF-based dehumidification can require less energy than silica-gel based system. • Three different mechanisms for improved energy performance in MOFs are articulated. • MOF-841, Co 2 Cl 2 (BTDD), Al-fumarate and CAU-23 performed best of the MOFs analyzed. Sorbent wheels are used in air conditioning systems to aid in dehumidification. The sorbents conventionally employed in these devices have linear, Type I or II water sorption isotherms requiring high regeneration temperatures. Metal Organic Frameworks (MOFs), a new class of sorbent materials, can be regenerated at much lower temperatures thanks to their Type IV or V isotherms and steep adsorption step. In this work we investigate the benefits of using MOFs as sorbents in dehumidification wheels in air conditioning systems. We first develop a first-principles model of a typical system in the Modelica language and validate it with experimental data . We then investigate the effect of replacing the most commonly used solid sorbent, silica gel, with each of several systematically selected MOFs. Our results show that the best performing MOFs of the candidates tested (Co 2 Cl 2 (BTDD) (Co), Al-fumarate (Al) or CAU-23 (Al)) can regenerated at temperatures as low as 40–60 °C depending on ambient conditions, in contrast to 80–140 °C for silica gel. Also, energy requirements of a MOF-based sorbent wheel can be from 1/2 to 1/8 of the energy required for silica gel-based systems depending on ambient conditions.