The material also binds less strongly to water molecules. That reduces the amount of heat needed to free the water molecules—making the process more efficient—and speeds up the process of adsorbing and desorbing water by 50 to 100 times, which helps make the chiller smaller. The materials also work with refrigerants other than water, which expands the temperature range at which cooling is possible.
Since current adsorption chillers can be two or three times larger than chillers that use electric compressors, “cutting the size of adsorption chillers by 75 percent could make them competitive,” says Yunho Hwang, a professor at the Center for Environmental Energy Engineering at the University of Maryland. The chillers could be particularly useful for cooling with hot water from solar water heaters, since adsorption chillers can use the relatively low-temperature such heaters produce, he says.
One challenge for such applications could be synchronizing demand for cooling with the production of heat—in some cases, it may be necessary to include a costly heat-storage system to make it possible to keep the chiller running after the sun goes down.
The PNNL researchers have been awarded $2.54 million from the Advanced Research Projects Agency for Energy to demonstrate the material in a cooling system. Under the grant, they have three years to optimize the material’s performance and incorporate it into a small demonstration chiller.