In ultralow-temperature freezers, there’s one big question: How low to go?
The standard in ultralow-temperature freezers is –80° Celsius. It’s so common that many scientists even call them –80 freezers. Does that make –80 °C a magic number? According to some top experts, there’s no magic in –80. “The important thing to remember about –80 °C is that it was not chosen based on scientific evidence,” says Allison Paradise, executive director at My Green Lab (Los Gatos, CA). “There is no evidence that –80 °C stores samples better than –70 °C.” That’s the driving force behind the –80 takedown. It might be time to turn up your freezer’s thermostat.
When asked about the source of –80 °C as a standard, Star Scott, green lab program coordinator at the University of Georgia, Athens, says, “It was industry-driven.” When technology made it possible to make a freezer colder, –80 °C came on the market, with higher price tags. “Researchers adopted this newer technology as ‘better,’ assuming that it would be better for their samples, and it became a standard,” Scott explains.
If –80 °C is not a magic number, what makes –70 °C any better? It is cold enough, but not colder than necessary, which is wasteful. Paradise and her colleagues compared the energy used in ultralow-temperature freezers (ULTs), and showed that going from –80° to –70° saved 20–50%. The average was 37%. “On a standard ULT freezer, this is equivalent to about eight kilowatt-hours per day,” Paradise points out. This is equivalent to the carbon sequestered by a two-acre forest annually.
Sample safety
Although scientists, universities, industry, and government labs strive to get greener—at least more than they have in much of the past—the reason for sticking with –80 °C on a ULT is usually explained as a safety precaution, keeping samples safe. Is everything safe at –70 °C? Maybe not everything, but certainly many samples.
Scientists at the University of Colorado Boulder, University of California Davis, University of California Riverside, and University of California San Diego have shown the sample types that they are storing at –70 °C or warmer. Scientists can explore this database online (http://bit.ly/2xGTqV6). “The database is not science-based, but shows cold-storage temperature practices that these labs are using,” says Kathryn Ramirez-Aguilar, manager of the green labs program at the University of Colorado Boulder.
In some cases, –80 °C is complete overkill. “Many samples stored in these units, such as DNA, can actually be stored safely at –20 °C,” says Scott.
Setting new standards
Given that many samples can be stored safely at –70 °C and it saves so much energy, is everyone making the switch? No. In a 2016 study, Paradise and her colleagues found the average ULT temperature to be –77.5 °C. Although that is a little warmer than –80 °C, it could mean that some scientists have turned up the thermostat or that enough older ULTs are still in use that can’t get down to –80 °C. “Based on the work we do in labs, I think the vast majority are still set to –80 °C,” Paradise says. “We’re still trying to get the message out that –70 °C is the new –80 °C.”
Scott adds that most of the ULTs on her campus are set at –80 °C. ‘The reason for this is that most researchers would rather be ‘safe than sorry,’ and I don’t blame them,” she says. “They really don’t have the time—or energy or desire—to research storage temperatures, and while we provide them with as much information as we can, much of it is anecdotal and not from published peer-reviewed journals.” She adds that if researchers paid their own electric bills, the scientists might be more likely to turn down the ULT dial.
Some universities are gaining ground in the –80 °C. “At CU Boulder, approximately half of all our ULT freezers are set at –70 °C, because we have many very engaged scientists who care about their environmental footprint,” says Ramirez-Aguilar. “As a result, the standard at CU Boulder has become both –70 °C and –80 °C.”
In addition to setting the thermostat up on older ULTs, ENERGY STAR recently released a standard for these freezers. So, scientists can pick an ULT that is super-efficient.
Getting more labs thinking about ULT energy use spawned Paradise and her colleagues to develop The North American Laboratory Freezer Challenge. “In 2017, we had over 200 labs participate and we saved an estimated 2.7 million kilowatt-hours per year,” she says. They will run the challenge again in 2018.
It’s time for the –80 °C takedown. Check the list of samples that stay safe at –70 °C, and turn down the dials where possible.