Ever since the development of vapor-compression refrigeration in the early 20th century, chemists have constantly been tinkering to find more efficient and cost-effective refrigerants. Until the late 1980’s, the most common refrigerants were chlorofluorocarbons, or CFCs. CFCs are organic compounds made up of carbon, chlorine, and fluorine (derived from methane, ethane, and propane), and are best known by their DuPont brand name: Freon. However, CFCs were found to be contributing to the depletion of the ozone layer, and in 1987 the multi-national Montreal Protocol on Substances that Deplete the Ozone Layer was agreed upon, which involved phasing out CFCs as refrigerants.
As CFCs were phased out throughout the 1990s, their primary replacements as refrigerant were hydrofluorocarbons, or HFCs. HFCs contain hydrogen atoms instead of the chlorine atoms found in CFCs. One of the most prolific HFCs, 1,1,1,2-tetrafluoroethane (known more commonly as R-134a), is used by Powers Scientific in all our refrigerated chambers. HFCs are an upgrade over CFCs in that they are much less destructive to the ozone layer. However, they are not a perfect solution. As concerns about climate change continue to grow, HFCs have come under scrutiny for their global warming potential (GWP). As the levels of HFCs in the atmosphere continue to increase, so does the climate risk. To keep this emergent environmental danger in check, world leaders met in Rwanda last October to make a deal to lower HFC usage. They agreed to lower the worldwide usage of HFCs by 80-85% by 2047.
Over the next 30 years, new refrigerants and new refrigeration techniques must step up to fill the demand that will be left by the phasing out of HFCs. These new refrigerants will need to be able to quickly break up in the atmosphere and reduce the global warming impact compared to HFCs. HFO-1234yf, a hydrofluoroolefin, has starting to be used in some car air conditioners as a replacement for R-134a. HFO-1234yf has a GWP that is only 1/335 of the GWP of R-134a, and has a lifespan in the atmosphere that is 400 times shorter than HFCs. There are some concerns about the potential flammability of HFO-1234yf in some applications, so its use beyond the automotive industry is currently limited.
In addition to using new refrigerants in traditional vapor-compression refrigeration systems, there is also the option to use new refrigeration systems entirely. Powers Scientific has begun using thermoelectric coolers (also called Peltier coolers) in several of our Drosophila chamber models. Thermoelectric coolers work by running a direct electric current between two parallel semiconducting plates. As the current travels between the plates, it carries heat from one side to the other. If the “cold” side is connected to an area to be cooled (say, the inside of a refrigerator), and the “hot” side is connected to a heat sink, then this system can produce results like a traditional vapor compression system without requiring any gases or even any moving parts at all.
There are several advantages to using a thermoelectric cooler over a traditional vapor compression system. First, the thermoelectric cooler has no moving parts, so maintenance is easier. They have long lifetimes so they need to be replaced less often. Also, there is no possibility of breakdowns associated with leaking refrigerant since the entire system is liquid-free. Further, it can provide very tight temperature control. The only downside is the they are not capable of generating large changes in temperature from the ambient (at least not efficiently), so they are currently limited to applications that don’t require large amounts of cooling. Since drosophila experiments are often carried out from 18°C to 25°C, which is close to ambient temperature, thermoelectric coolers can meet the temperature requirements of the research while eliminating the chance of mechanical failure and providing an overall eco-friendlier unit.