![Revco_-80_freezer_pl](https://upload.wikimedia.org/wikipedia/commons/6/6b/Revco_-80_freezer_pl.jpg)
An ultra low temperature (ULT) freezer is a
refrigerator
A refrigerator, colloquially fridge, is a commercial and home appliance consisting of a thermally insulated compartment and a heat pump (mechanical, electronic or chemical) that transfers heat from its inside to its external environment so th ...
that stores contents at between .
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.
ULT freezers come in upright and chest freezer formats.
Application
![ALSPAC_biological_samples_in_freezer](https://upload.wikimedia.org/wikipedia/commons/3/35/ALSPAC_biological_samples_in_freezer.jpg)
In contrast to short term sample storage at by using standard
refrigerator
A refrigerator, colloquially fridge, is a commercial and home appliance consisting of a thermally insulated compartment and a heat pump (mechanical, electronic or chemical) that transfers heat from its inside to its external environment so th ...
s or freezers, many
molecular biology
Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and physi ...
or
life science
Life is a quality that distinguishes matter that has biological processes, such as signaling and self-sustaining processes, from that which does not, and is defined by the capacity for growth, reaction to stimuli, metabolism, energy t ...
laboratories need long-term
cryopreservation
Cryo-preservation or cryo-conservation is a process where Organism, organisms, organelles, cell (biology), cells, Biological tissue, tissues, extracellular matrix, Organ (anatomy), organs, or any other biological constructs susceptible to damage ...
(including "
cold chain
A cold chain is a low temperature-controlled supply chain network. An unbroken cold chain is an uninterrupted series of refrigerated production, storage and distribution activities, along with associated equipment and logistics, which maintain qu ...
" and/or "
colder chain" infrastructures) for biological samples like
DNA,
RNA
Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...
,
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s, cell extracts, or reagents. To reduce the risk of sample damage, these types of samples need extremely low temperatures of . Mammalian cells are often stored in
dewars
Dewar's () is a brand of blended Scotch whisky owned by Bacardi, which claims the brand's "White Label" to be the top-selling blended Scotch in the US. Dewar's is also the world's most awarded blended Scotch whisky with more than 1,000 medals ear ...
containing
liquid nitrogen
Liquid nitrogen—LN2—is nitrogen in a liquid state at low temperature. Liquid nitrogen has a boiling point of about . It is produced industrially by fractional distillation of liquid air. It is a colorless, low viscosity liquid that is wide ...
at . Cryogenic chest freezers can achieve temperatures down to , and may include a liquid nitrogen backup.
Biological samples in ULT freezers are often stored in
polymer
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
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.
![Lab_Freezer_(149437499)](https://upload.wikimedia.org/wikipedia/commons/a/ac/Lab_Freezer_%28149437499%29.jpg)
ULT freezers are widely used in fish and meat preservation. The tuna fishing industry requires the use of ULT freezers.
ULT freezers are commonly fitted with alarm systems that will remotely alert designated parties in the case of a freezer failure.
Pull down time
The pull down time is defined as the necessary time to cool down the ULT freezer from ambient temperatures to the selected temperature of . 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.
Energy consumption
Due to the low temperature, ULT freezers consume high amounts of
electric energy
Electrical energy is energy related to forces on electrically charged particles and the movement of electrically charged particles (often electrons in wires, but not always). This energy is supplied by the combination of electric current and electr ...
and hence are expensive to operate. In 2010,
Stanford University
Stanford University, officially Leland Stanford Junior University, is a private research university in Stanford, California. The campus occupies , among the largest in the United States, and enrolls over 17,000 students. Stanford is consider ...
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.
Nonetheless, a comprehensive report published in 2015 by the Center for Energy Efficient Laboratories (funded by
Pacific Gas & Electric
The Pacific Gas and Electric Company (PG&E) is an American investor-owned utility (IOU). The company is headquartered in the Pacific Gas & Electric Building, in San Francisco, California. PG&E provides natural gas and electricity to 5.2 milli ...
,
Southern California Edison
Southern California Edison (or SCE Corp), the largest subsidiary of Edison International, is the primary electricity supply company for much of Southern California. It provides 15 million people with electricity across a service territory of app ...
, and
San Diego Gas & Electric
San Diego Gas & Electric (SDG&E) provides natural gas and electricity to San Diego County and southern Orange County in southwestern California, United States. It is owned by Sempra, a Fortune 500 energy services holding company based in San Dieg ...
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.
In recent years, some scientists have began suggesting that laboratories set freezers to –70 °C instead of –80 °C to conserve energy and decrease wear on the freezer's compressor.
Depending on the volume of the freezer, the opening frequency of the users as well as the number of samples, the
energy consumption
Energy consumption is the amount of energy used.
Biology
In the body, energy consumption is part of energy homeostasis. It derived from food energy. Energy consumption in the body is a product of the basal metabolic rate and the physical activity ...
starts from ca. 11 kWh/day and higher. To reduce the energy consumption, the
insulation
Insulation may refer to:
Thermal
* Thermal insulation, use of materials to reduce rates of heat transfer
** List of insulation materials
** Building insulation, thermal insulation added to buildings for comfort and energy efficiency
*** Insulated ...
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.
Refrigeration cycle
ULT freezers that employ the
cascade refrigeration
A cascade refrigeration cycle is a multi-stage thermodynamic cycle. An example two-stage process is shown at right. (Bottom on mobile) The cascade cycle is often employed for devices such as ULT freezer
An ultra low temperature (ULT) freezer is ...
(CR) system use up to 20 times the energy footprint of household fridges, and used to refrigerate with
greenhouse gas
A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse ...
fluids (typically
hydrofluorocarbon
Hydrofluorocarbons (HFCs) are man-made organic compounds that contain fluorine and hydrogen atoms, and are the most common type of organofluorine compounds. Most are gases at room temperature and pressure. They are frequently used in air conditi ...
R-508B).
Modern ULT freezers employ HC (i.e.
hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...
) gas mixtures: typically,
ethane
Ethane ( , ) is an organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petr ...
and
propane
Propane () is a three-carbon alkane with the molecular formula . It is a gas at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used a ...
. This has also improved their efficiency by up to 30% over the conventional CFC or HFC gassed freezers.
See also
*
Dry ice
Dry ice is the solid form of carbon dioxide. It is commonly used for temporary refrigeration as CO2 does not have a liquid state at normal atmospheric pressure and sublimates directly from the solid state to the gas state. It is used primarily a ...
References
{{DEFAULTSORT:Ult Freezer
Cooling technology
Preservation methods