Most biological materials from simple biomolecules like oligonucleotides and proteins to complex entities like cells and tissues are sensitive to heat. In order to store these materials for analysis and characterization, they have to be stored in ultralow temperature (ULT) freezers that go as low as -80°C. In some cases, users may even consider cryogenic freezers that can go as low as -150°C for longer periods of sample storage. Previously, we have discussed the operating mechanisms of ULT freezers and, subsequently, their role in storing and transporting SARS-CoV-2 vaccines that are based on mRNA or proteins. Here, we will provide a guide into the factors to consider when purchasing ULT freezers and ongoing innovations to improve their functionality.
Factors to consider when purchasing a ULT freezer
A variety of factors come into the picture before purchasing ULT freezers. Besides cost, other considerations include freezer capacity, physical footprint, and energy efficiency.
Capacity: The capacity of the ULT freezer is an important factor to consider because it impacts the total amount of biological materials that can be stored. Generally, the larger the freezer volume, the more costly it will be to buy and operate. Therefore, if only a small storage volume is needed, a smaller ULT freezer is preferred as it will lead to lower long-term operating costs and smaller physical footprint.
Physical footprint: Lab space can be limited, and it is best if the ULT freezer takes up minimal space so additional space can be freed up for other lab purposes. Upright ULT freezers have less physical footprint compared to the chest design. Upright ULT freezers also tend to have larger volumes and are therefore preferred for most labs. However, for labs that may have researchers who face physical challenges in height and mobility, the chest design is much more inclusive.
Energy efficiency: ULT freezers are typically equipped with designs such as double doors, gasket seals and polyurethane heat insulation to maximize energy efficiency. However, depending on the type of refrigerant and compressor they have, they can differ significantly in terms of their energy consumption. For instance, Thermo Fisher Scientific lists ULT freezer products with up to a 50 percent difference in their energy consumption (8 versus 12 kWh/day), which can lead to significant differences in long-term operating costs.
Temperature uniformity: Biological samples such as patient tissues are precious and can be hard to come by, and thus it is of paramount importance that ULT freezers are able to provide uniform temperature. One of the most important factors affecting the temperature homogeneity is recovery time to -80°C after warm air outside the freezer rushes in during door opening. It is preferable to get ULT freezers with multiple inner doors for different storage shelves instead of a single inner door for the entire freezer. This way, only the temperature of the shelf of interest is affected during door opening, and it consumes less energy to reset the freezer’s interior temperature.
Backup cooling: Cooling technology in ULT freezers normally uses the cascade refrigeration system which requires electricity. However, when electrical supplies are disrupted, cooling ends and the integrity of stored biological samples will be compromised. Hence, it is also useful to consider whether ULT freezers have a back-up cooling system or if such a system can be added at an additional cost. The typical choice of back-up cooling system is liquefied nitrogen (maintains temperature down to -80oC) or carbon dioxide (maintains temperature down to -70°C).
Noise: As a result of the intensive fan-cooling needed, ULT freezers can be a significant source of noise in the lab. Noise can distract researchers and even reduce their productivity. ULT freezers come with different noise levels. Generally, the larger the freezer, the louder the noise they generate as they need to be cooled down more substantially to provide uniform temperature. Manufacturers usually provide the noise level generated by ULT freezers—as a point of reference—a normal conversation generates about 60 decibels although the enclosed area of labs can amplify the noise intensity.
User interface: Newer designs of ULT freezers can be connected to Wi-Fi and be remotely controlled. This can be useful in situations where it is important to monitor freezer temperature during non-working hours or in situations when the pandemic disrupts in-person lab activities. Some user interface options include buttons and touchscreens that researchers can use to access freezer information like voltages and numbers of door openings, and adjust settings like the set temperature, allowable temperature range, and alarm.
Innovations in ULT freezers
ULT freezers are essential pieces of equipment for biological research. Over the years, their designs have become more innovative to enhance their reliability to preserve sample integrity while reducing operating costs and improving ergonomics.
Sample integrity: There is an increase in the numbers of biobanks for storing precious biological samples for analysis. These endeavors require reliable ULT freezers to protect the integrity of samples. Newer freezer designs come with back-up cooling in case of electrical disruption or failure and remote access for alarm notifications. Furthermore, by incorporating more efficient fan cooling technology and frost-resistant gasket door seals, door opening recovery time is reduced to provide uniform temperature. For instance, newer ULT freezer products from Eppendorf use vacuum insulation panel technology that reduces heat transfer from the external environment into the freezer much better than conventional materials like polyurethane and foam beads. Most ULT freezers still come with start-stop compressor systems but companies like Stirling Ultracold have come up with helium-charged piston engines that run continuously to eliminate surge currents and mechanical failures that could compromise sample integrity.
Environmental sustainability: With increasing awareness of the carbon footprints from research labs, manufacturers are also improving their designs. The compressors used are more efficient now and are even equipped with learning algorithms to optimize energy consumption. Users can look out for certification such as that from ENERGY STAR® to identify products that are more environmentally friendly. Refrigerants used in ULT freezers nowadays are also mostly free from harmful greenhouse gases like chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFC). Additionally, high-quality materials used as insulators and gasket seals also help to reduce the energy consumption needed to maintain freezer interior temperature.
Ergonomics: Noise from ULT freezers can be a significant source of disturbance in enclosed lab spaces. Manufacturers like Arctiko have managed to reduce noise level to just 49 decibels. Other ergonomic designs include having access panels at eye level to enable comfortable inspection, introducing castor wheels to facilitate relocation of freezers, and shaping door handles in the form of a hand grip for easy door opening.
Easy maintenance: Manufacturers have also introduced innovative materials with anti-frost properties to reduce frost and ice build-up that can be cumbersome to remove while adversely affecting temperature uniformity.
A variety of ULT freezer products exist on the market. Depending on their needs and preferences, users have diverse models to choose from based on the scale of their lab operation, budget, space, and institutional environmental policies.