A Matter of Degrees: Together, Forward, Warmer?

This piece is the first installment of a four-part series, ‘I’m Glad You Asked,’ an uncomplicated, unabashed exploration of the individual and collective actions needed to lay the groundwork for a climate and future-friendly laboratory.

Since rising to prominence in the late 1970s, ultra-low temperature (ULT) freezers have played an indispensable role within the life sciences. Depending on the size of your lab and its needs, you may have numerous ULT units, each of which housing samples built on years – if not decades – worth of research.

In fact, estimates show that a single ULT freezer stores product with an average value of $750,000, though many would contend that their samples are truly priceless. Needless to say, ULT freezers are entrusted to store the very biospecimens, enzymes and drugs needed to drive innovation and therefore human health forward.

When looking at the evolutionary arc of the ULT freezer, it becomes clear that much has changed over the course of the product’s relatively short existence. As seen in the 1980s, early chest freezer models, prized for their reliability, were able to reach temperatures of -75℃ using pure CFC refrigerants, an ozone-depleting compound now outlawed by the Montreal Protocol. Today, upright ULT units using hydrocarbon, or ‘green refrigerants’ are the norm, achieving temperatures upwards of -85℃.

While ULT units have been designed to require less energy through the use of more efficient refrigerant pumping mechanisms and compressor systems, they have yet to shake their reputation as the lab’s energy hog. In theory, advancements in insulation and temperature regulation technology should yield a product with a smaller energy footprint. Yet, studies have shown that a single ULT freezer today uses 20 kWh of energy daily, the equivalent energy consumption of the average U.S. single-family home.

When coming to terms with the sheer energy requirements of the ULT freezer, some turn to scrutinizing the freezer itself, while others are inclined to frame it as a ‘necessary evil.’ Fewer, though, explore the possibility that such a resource drain stems from an unquestioned practice, one rooted in cultural inertia as opposed to hard proof. How is it that we settled on -80℃ for sample preservation anyways, and what are the consequences of straying from the consensus?

As it turns out, the ‘minus 80’ standard is somewhat arbitrary. Allen Doyle, a longtime Sustainability Manager at both UC Davis and UC Santa Barbara, attributes the adoption of -80℃ to what he calls the ‘cold creep.’ With newer, more efficient models entering the market, labs were compelled to make use of default colder temperatures to ensure optimal sample integrity. Today, in recognizing the unchecked influence of cold creep, a growing list of laboratories across the U.S. have begun ‘chilling up’ their ULT freezers to the previous industry standard of -70℃.

While such a move warrants a larger lab or institution-wide conversation, the switch has proven itself a success for many. Labs have found that the 10 degree differential is capable of saving 1,000 kWh of energy per year, while also translating into further cost-savings and reduced wear and tear.

So then, what is there to be said about any potential impacts on sample preservation? Industry leaders in the ULT freezer space have suggested that nucleic acids, proteins, bacteria and viruses can be safely stored at -70℃ in most cases. Certainly, this switch should be assessed against the specific needs of your samples, though the variation is not all that drastic. For many older models which struggle to cool evenly but are still widely in use, temperatures tend to vary within this range as is.

As we look to charter a path towards the low-impact lab of the future, we will need to question and think critically about the assumptions that guide our work. Adjusting ULT unit temperatures alone will not suffice, nor will purchasing energy-star compliant equipment or scheduling regular de-icings (we recommend doing all of these!). Together, though, in concert with other actions that look to minimize resource usage and waste, such actions will serve as an impact multiplier.