Ultra low temperature freezer

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Ultra low temperature freezer

An ultra-low temperature freezer is used for long-term storage of critical biological samples such as deoxyribonucleic acid (DNA), ribonucleic acid (RNA), proteins , vaccines , cell extracts or reagents in molecular biology or life science laboratories. These samples must be stored at extremely low temperatures of −80 ° C to −85 ° C to avoid the risk of damage to the ingredients.

principle

In biological research, it is often necessary to collect samples and keep them for later study and analysis. If the process of storing them is not effective, i.e. if the cold chain is not properly followed, biological samples, for example, can be damaged during the period in which a sample was taken and analyzed. These samples are usually stored at low temperatures, including refrigeration (−40 ° C), freezers (−50 ° C to −80 ° C), and liquid nitrogen (−170 ° C). This goes far beyond short-term sample storage in standard refrigerators (+4 ° C) or freezers (−20 ° C). They can be classified into three types based on the temperature range of their operation as follows:

  • Freezer at −60 ° C: For storage of plasma, biological material, vaccines and reagents
  • Freezer at −86 ° C: For storing biological products, serum, vaccines, bacteria and biological samples such as cryopreservation
  • -105 ° C to -150 ° C freezer: Typically used in research institutes, biotechnology, blood banks, hospitals, university laboratories, and military companies

The temperature profile in the cooling room is recorded so that it can be understood whether sufficient cooling was guaranteed at all times.

Cascade cooling system

Schematic representation of a cascade cooling process with two cycles

ULT Freezers use a cascade cooling system to provide effective cooling conditions for the safety of the stored samples. Each cooling section is managed by its own microprocessor controller. If one of the systems fails, an internal control system issues an audiovisual alarm and the damaged system is stopped. Then the second system turns on to maintain the internal temperature. The system uses two compressors . Low temperature laboratory freezers, which generally operate at around −40 ° C, use a single compressor. A second compressor is required to cool the cooling chamber below this point to −80 ° C. The energy efficiency and longer life of the compressors can be achieved by automatically switching off the low stage compressor when the set temperature (desired temperature) is reached, while the high temperature stage compressor remains on continuously.

functionality

In operation, the heat exchange coil is cooled when the first stage (high temperature) compressor starts. Then, when a second level (low temperature) compressor operates, its cooling system condenses in the first and second level heat exchanger coils. The system reduces the temperature of the refrigerator to below −80 ° C or −90 ° C. When the power is turned on, the display temperature is higher than the set temperature. This will cause the first stage compressor to start to run the refrigeration system. This lowers the temperature at the condenser of the second stage cooling system and the refrigerant temperature of the second stage. At this stage, the second stage cooling system begins to work.

Coolant

Greenhouse gases were previously used as coolants , preferably fluorocarbon R-508B, now environmentally friendly refrigerants such as R-290 ( propane ) or R-170 ( ethane ). Lately, the shipping of frozen and ultra-frozen substances in dry ice boxes has become the standard. Transport containers with regulated cooling for temperatures down to −80 ° C are now also available for shipping at −20 ° C.

Vaccines

Some of the vaccines against the COVID-19 disease - caused by the SARS-CoV-2 virus - that are currently being developed must be transported and stored frozen at −70 ° C. Appropriate ultra-low temperature freezers must be available for this. Suppliers such as Va-Q-tec or Binder specialize in such ultra-low temperature freezers.

Air freight

One difficulty with transporting vaccines is that airplanes are only allowed to transport a limited amount of dry ice, as it sublimates into gas over time and displaces the breathable air in the cabin - even if the cabin is always supplied with fresh air from outside. According to a DHL whitepaper on vaccine transport, all wide-body aircraft can transport a maximum of one ton of dry ice in cooled and thermally insulated containers. The FAA has allowed during the Covid-19 pandemic the airlines to carry into the cooling containers up to 6800 kg of dry ice per aircraft. One condition for this was that the crews were informed about the symptoms of carbon dioxide poisoning and the corresponding precautionary measures. As an alternative, DHL uses Cryoport's capsule containers , which use liquid nitrogen to keep goods cool down to −150 ° C for up to 10 days. In contrast, there are so-called active containers, such as envirotainers , which use electric motors to cool their contents.

swell

Web links

Individual evidence

  1. ↑ David Berchowitz, Yongrak Kwon, Environmental Profiles of Stirling Cooled and Cascade-Cooled Ultra-Low Temperature Freezers, 2012 Sustainability, Volume 4, Issue 11, pp 2838-2851, doi : 10.3390 / su4112838
  2. ↑ Ultra-low freezers with climate-neutral refrigerants , binders. Retrieved November 25, 2020.
  3. ↑ Delivering pandemic resilience , DHL, September 2020. Accessed November 23, 2020.
  4. ↑ Health ministers decide on vaccination strategy , Tagesschau, November 7, 2020. Accessed November 9, 2020.
  5. ↑ Va-Q-tec: The main thing is to stay cool Zeit.de, December 2, 2020
  6. ↑ Alison Sider and Peter Loftus: United Begins Flying Pfizer's Covid-19 Vaccine. In: Wall Street Journal. November 27, 2020, accessed on December 22, 2020 .
  7. ↑ Airlines scramble to prepare for ultra-cold COVID-19 vaccine distribution , Reuters, November 18, 2020. Accessed December 21, 2020.