From the ongoing research into refrigerants and lubricants, another type of refrigerant additive has emerged. Lubricants called nanolubes, which are based on the use of nanoparticles, show some promise to be a cost-effective efficiency booster for air-conditioning systems. These new additives use tiny particles—composed of either metal oxides or carbon—that are no larger than a virus cell. The metal oxides used are classified as advanced or technical ceramics, not to be confused with traditional ceramics that are commonly associated with pottery or tile. Traditional ceramics are silicate-based and crystalline in nature, giving them their brittle, nonconductive characteristics. Advanced ceramics, on the other hand, can exhibit a plethora of superior characteristics, including thermal conductivity. Because these additives are more thermally conductive than refrigerant oil, it’s plausible that they have the potential to improve heat transfer in refrigeration systems by a large enough margin to make a significant difference in overall efficiency.
Mark Kedzierski from NIST has also been researching nanolubes. He was part of a research team that documented an enhancement to the heat-transfer rate of a system by as much as 275 percent by adding copper-oxide nanoparticles. According to Kedzierski, this type of refrigerant additive is attractive because the nanoparticles are very cheap. The challenge is to produce a solution that’s concentrated enough to be poured into a refrigeration system without having to drain and filter out any of the existing oil. NIST, with funding from the US Department of Energy, is working to commercialize this technology. Kedzierski says it will likely take another couple of years to figure out whether a viable product can be commercially produced.
NIST is not alone in its attempt to commercialize nanolubes. ACTA Technology—a Boulder, Colorado, start-up—is aiming to commercialize its own product made from charged carbon nanotubes, which are about four times more conductive than copper. Ed Clancy, the chief technical officer at ACTA, claims that in lab tests, his product has improved the thermal conductivity of an oil and refrigerant mixture by 194 percent. However, at the moment, ACTA has been unable to secure additional funding, so development has been paused. It is, however, pursuing another additive for use in ground-source heat pumps. Clancy told us that adding nanoparticles to the fluid in this case increased heat transfer by 48 percent.
Additionally, Kedzierski mentioned that there may be some competition from abroad—reportedly, a team in China claims to have improved the efficiency of a refrigerator by 9.6 percent using titanium-dioxide nanoparticles.