New research at Pacific Northwest National Laboratory (PNNL) has uncovered a new way to create an improved metal-organic framework (MOF) for adsorption cooling.
Adsorption cooling systems depend on a solid adsorbent and a refrigerant, which transform heat into energy for cooling when they interact. This process can be driven by waste heat from an industrial plant, for example, or heat from the sun, but the compatibility of the adsorbent and refrigerant influences how well it works.
The new study, published in the Journal of the American Chemical Society, tested how R134a performed at the atomic level with MOFs manipulated to contain a high pore volume and density of open metal centers. The researchers noted a dramatic increase in the efficiency of their pore-engineered MOFs.
“By increasing the saturation limits, we allow more ﬂuorocarbon to be taken up by the sorbent per cycle of adsorption and desorption based on specified chiller process conditions,” says PNNL materials scientist Radha Kishan Motkuri, who has developed fluorocarbon and water-based adsorption cooling systems for 10 years, and who led the research team.
“This increased throughput translates to a 400 percent increase in the theoretical working capacity to cycle between adsorption/desorption state points. Ultimately, correlation of its bulk sorption performance under realistic chiller conditions results in modeled cooling capacities that are at least 40 percent larger than that of the parent MOF.”
The system uses the same refrigerants and evaporator/condenser components as conventional refrigeration and air conditioning systems, which enables them to be integrated.
According to an article on the PNNL website, the electric-powered compressor can be turned off when heat is available, for example, from a solar panel or geothermal resource, to run an MOF-based thermal compressor. Sorption-based cooling systems thus could ease the stress on electricity supplies.
The research builds on PNNL’s “MARCool” technology, which created a new class of solid-state cooling technology and won a 2017 R&D 100 Award.