Solar Refrigerator Air Conditioning Adsorption Refrigeration Unit Refrigeration No electricity

It will soon be possible to cool the building more practically, using solar water heaters and generator waste heat. This is because researchers at the Pacific Northwest National Laboratory have developed a new type of porous material. These materials can improve a process called adsorption cooling that can be used in refrigerators and air conditioners.

Thermal compression: The presentation at a conference shows that there is a new material (light green) that can be compressed into a metal foam. This material is used to improve the technology, using thermal energy to drive the cooling process.

Adsorption chillers are too large and expensive, and this is true for many applications, such as in home use. Peter McGrail was responsible for this research. He predicted that the material could reduce the adsorption refrigerator by 75% and the price by half. This will allow them to compete with traditional, compressor-driven chillers.

All refrigerators and air conditioners need to evaporate a refrigerant, which can absorb heat. The difference between them is how to compress the refrigerant so that it can be recycled for cooling. The difference is that most of the technologies used in air-conditioning are electric-driven compressors that mechanically compress vaporized refrigerants, whereas the adsorption-type refrigeration units use heat to compress the refrigerant. Adsorption refrigeration units are generally not efficient enough, much lower than refrigerators using electric compressors, and they are bulky and expensive. But they also have the advantage that they can be cheaply run because they only require very little electricity. "If you have excess heat, you can run for free," McGellar said.

To date, these units have been limited to applications where there is a lot of waste heat, such as industrial and power plants, or where electricity is not always available. Reducing their size and cost, they can attract more applications, including at home, where they can operate using hot water from solar water heaters, McGellar said.

The key is to improve the solid adsorption material. In an adsorption refrigeration unit, the evaporated refrigerant is adsorbed on a solid surface, such as silica gel. Silicone can hold a lot of water, only a small space, it can essentially be used as a sponge for water vapor. When the silica gel is heated, it releases the water molecules into a container. As the concentration of water vapor in the container rises, the pressure rises until the water condenses.

McGellar is replacing silicone and uses an engineering material that requires the creation of nanoscale structures that can be assembled on their own to form complex three-dimensional shapes. This material has more pores than silica gel, giving it a larger surface area allowing water molecules to adsorb. Therefore, it can capture 3 to 4 times more water, which is based on weight, compared to silica gel, which helps to reduce the size of the chiller.

The combination of this material with water molecules is also not very strong. This reduces the amount of heat required to release water molecules, making this process more efficient and accelerating the process of water adsorption and desorption, which can be 50 to 100 times faster, which helps to make the unit smaller. The refrigerant that can be used in this material is not only water, it expands the range of possible cooling temperatures.

Since current adsorption refrigeration units are two to three times the size of electric compressor chillers, “reducing the size of adsorption refrigeration units by 75% will make them competitive,” said Yunho Hwang, who is Professor at the University of Maryland Environmental Energy Engineering Center.

This kind of refrigerator is particularly beneficial, and the solar water heater can be used for the cooling of hot water, because the adsorption refrigeration unit can use a relatively low temperature, such as the temperature generated by the water heater, he said.
There is a challenge. For such applications, it is the need for simultaneous cooling and production heat. In some cases, it may be necessary to include an expensive thermal storage system to keep the chiller running after sunset.

Researchers at the Pacific Northwest National Laboratory have received $2.54 million from the Advanced Research Projects Agency for Energy to demonstrate this material in the cooling system. Relying on these funds, they have three years to optimize material properties and integrate it into small demonstration units.