A couple decades ago, all Ultra-Low Temperature (ULT) freezers, equipment commonly found in laboratories, operated at –70ºC. The proliferation of –80ºC units only occurred after these became available and manufacturers heavily marketed them without any evidence of a scientific need for their lower temperatures. ULT freezers are extremely energy-intensive, drawing as much energy as the average U.S. household, so this shift has led to large increases in the electricity consumption of research facilities.

The push to chill up freezers, back to –70ºC, has gained momentum in recent years due to increasing urgency around climate change. Research institutions around the world have begun to make the switch and, through these changes, have found that adjusting ULT freezer temperatures to –70°C can reduce energy use while maintaining performance. A study by the Center for Energy Efficient Laboratories (CEEL) found that this small temperature increase reduces energy consumption by an average of 37% for both standard-efficiency and energy-efficient ULT freezers without any noticeable effect on sample stability. Additionally, raising freezer temperatures actually can extend freezer lifetimes by placing less strain on the compressor system, decreasing the chance of freezer failure.

This campaign has also gained momentum on campus through efforts by the Harvard Office for Sustainability and Green Labs Initiative. Research groups from across the Univeristy have made the switch to –70 ºC.

The first group to do so was the Nocera Lab in the Chemistry and Chemical Biology department. Dr. Dilek Dogutan, principal research scientist in the group, described the process of switching their ULT freezer as very safe, quick, and easy to do, with no noticeable impacts on their research. The group was motivated to change their freezer temperature to “save energy and save money.” Dr. Dougtan emphasized that doing a “thorough job of inventory” and consulting manufacturers and material safety data sheets to identify which reagents would remain stable up to –70ºC was essentially all that was necessary for a successful adjustment.

Another group that has made the switch to –70ºC is the Hoekstra Lab in the Department of Organismic and Evolutionary Biology, whose efforts in implementing sustainable lab initiatives led to them winning the National Green Labs Freezer Challenge in 2017. Kyle Turner, Hoekstra group lab manager at the time, said that they were motivated to switch to –70ºC because of lab biology’s “large footprint environmentally in terms of energy use.” Upon hearing about the lab freezer challenge held by the non-profit My Green Lab, Turner found and compared data on research institutions across the country and the reagents they stored at –70ºC to the samples studied in the Hoekstra Lab, and found them to be extremely similar. The lab collectively decided to adjust both of their ULT freezers to –70ºC.

When asked about concerns with long-term sample stability, Turner said that there was no reason to believe that samples that need long-term storage would undergo any detrimental changes upon a 10ºC warming of their ULT freezers. Additionally, extremely sensitive samples, that a slightly warmer temperature could impact, are often processed more quickly.

Action on climate change will require drastic and wide-reaching efforts, but there are also simple changes that can have large impacts on reducing energy consumption, especially in energy-intensive places like research facilities. Switching to ULT freezers to –70ºC could save Harvard almost $700,000 per year and lead to a reduction of greenhouse gas emissions of around 1,476.35 MTCDE (metric tons of carbon dioxide) annually, equivalent to taking over 100 cars off of the road, eliminating 58 homes worth of energy, or burning 1,128 fewer barrels of oil every year.