Anultra low temperature (ULT) freezer is arefrigerator that stores contents at −80 to −86 °C (−112 to −123 °F).^[1] An ultra low temperature freezer is commonly referred to as a "minus 80 freezer" or a "negative 80 freezer", referring to the most common temperature standard.^[2] ULT freezers come in upright and chest freezer formats.

In contrast to short term sample storage at +4 to −20 °C (39 to −4 °F) by using standardrefrigerators or freezers, manymolecular biology orlife science laboratories need long-termcryopreservation (including "cold chain" and/or "colder chain" infrastructures) for biological samples likeDNA,RNA,proteins, cell extracts, or reagents. To reduce the risk of sample damage, these types of samples need extremely low temperatures of −80 to −86 °C (−112 to −123 °F). Mammalian cells are often stored indewars containingliquid nitrogen at −196 °C (−320.8 °F).^{[3][failed verification]} Cryogenic chest freezers can achieve temperatures down to −150 °C (−238 °F) to −152 °C (−242 °F)^[4] and may include a liquid nitrogen backup.

Biological samples in ULT freezers are often stored inpolymer tubes and microtubes, generally inside storage boxes that are commonly made of cardboard, polymer plastics or other materials. Microtubes are placed in storage boxes containing a grid of dividers that typically permit 64, 81, or 100 tubes to be stored. Standard ULT freezers can store approximately 350 to 450 microtube boxes.^[5]

ULT freezers are widely used in fish and meat preservation.^[6] The tuna fishing industry requires the use of ULT freezers.^{[citation needed]}

ULT freezers are commonly fitted with alarm systems that will remotely alert designated parties in the case of a freezer failure.^{[citation needed]}

The pull down time is defined as the necessary time to cool down the ULT freezer from ambient temperatures to the selected temperature of −80 to −86 °C (−112 to −123 °F). The time strongly depends on the type of insulation, the efficiency of the compressor system as well as the installed metal shelves within the freezer. At the start of the twenty-first century, ULT freezers were able to cool down within 3 to 5 hours. Warm up time is typically 1/8 °C per minute.^{[citation needed]}

Due to the low temperature, ULT freezers consume high amounts ofelectric energy^[7] and hence are expensive to operate. In 2010,Stanford University had more than 2,000 ULT freezers, which used an estimated 40 billion BTUs of energy and cost the university $5.6 million annually. Newer ULT freezers consume less energy.^[8] Nonetheless, a comprehensive report published in 2015 by the Center for Energy Efficient Laboratories (funded byPacific Gas & Electric,Southern California Edison, andSan Diego Gas & Electric utility companies as part of their Emerging Technologies program) found that laboratories in California consumed an estimated 800 GWh/year, with ULT freezers being the greatest contributor to that total.^[9]

At least as early as 2018, some scientists suggested that laboratories set freezers to –70 °C instead of –80 °C to conserve energy and decrease wear on the freezer's compressor.^[10][11]

Depending on the volume of the freezer, the opening frequency of the users as well as the number of samples, theenergy consumption starts from ca. 11 kWh/day and higher. The US government calculates 20 kWh/day.^[12] A study performed at theUniversity of Edinburgh showed that the New Brunswick U570 HEF model consumed slightly under 10 kWh/day.^[13] Without any data, theUniversity of Michigan claimed that "older model" ULT devices could consume "up to 30 kWh/day".^[14] A sales pitch written in 2023 quoted "16-22 KWh of electricity per day".^[15]

To reduce the energy consumption, theinsulation should be as efficient as possible. Additional inner doors reduce the loss of temperature when opening the main door. Icing within the ULT freezer should be reduced to a minimum. Modern ULT freezers employ variable speed drives for both the compressors and fans. This has reduced energy consumption a further 30% to typically 8.5 kWh/day.^{[citation needed]}

ULT freezers that employ thecascade refrigeration (CR) system use up to 20 times the energy footprint of household fridges, and used to refrigerate withgreenhouse gas fluids (typicallyhydrofluorocarbonR-508B).^[7] Modern ULT freezers employ HC (i.e.,hydrocarbon) gas mixtures: typically,ethane andpropane.^[16][17] This technology was developed in the mid-1990s,^[18] and improved efficiency by up to 30% over the conventional CFC or HFC gassed freezers.^[19][20] Alternatively ULT freezers may use theStirling cycle in reverse (A Stirling cooler) for refrigeration.^[7]

• Dry ice

• Cooling technology
• Cryopreservation
• Preservation methods

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