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Please check out our Laboratory Freezer section for more information or to find manufacturers that sell these products.
In the life science lab, most valuable samples and materials are stored in refrigerator freezers. Key specifications for choosing a lab freezer include usage/application, freezer type, configuration, temperature range, temperature stability, and energy efficiency. A freezer temperature range of –20 to –40 °C provides safe and stable storage conditions for many types of cells and reagents. The quality and suitability of the lab freezer, however, are often taken for granted when in reality the lab may be using an outdated or even a malfunctioning unit.
Upgraded features for sample storage
Freezers for enzymes and biochemicals are generally maintained at around –20 °C. Blood, biological samples, and vaccines typically require temperatures of –30 to –40 °C. Laboratory freezers often resemble the freezers that many people have in their homes, but with upgraded features like auto-defrost and programmable alarms for research applications. Lab freezer interiors have customized shelves and storage compartments for samples.
Laboratory freezer configurations and functions
There are numerous sizes and configurations of laboratory freezers available, including undercounter, freestanding, double-wide, and chest freezer models. An initial consideration in choosing a freezer model is the amount of space available in the laboratory. Upright freezers occupy a smaller footprint, and it is easier to locate samples inside, but chest freezers retain cold air better and recover more quickly when opened.
Freezers can also be configured for general purpose or specialized as for specimen freezers, vaccine freezers, enzyme freezers, blast-proof freezers, and so forth. Although a specialty freezer may be a very attractive option, a general-purpose freezer paired with custom containers may well be adequate for your laboratory’s needs.
Freezers function best in rooms that are not overly warm—to spare the compressor—and with at least several inches of clearance around all sides to allow air circulation. Rooms containing freezers should be well-ventilated, again to allow cooling of compressors. Avoid placing too many freezers in one room. Regular maintenance, including defrosting, vacuuming vents, and changing air filters, can prolong the use life of the unit.
Lab freezers with auto-defrost
Temperature stability is one of the most important features of a laboratory freezer. The choice of a manual or auto-defrost freezer will depend on the stability needs of the samples stored inside. In an autodefrost freezer, the coils are heated on a regular cycle, causing periodic temperature spikes. Keeping the freezer completely full can minimize the size of the spikes. An empty auto-defrost freezer can vary up and down by as much as 15 °C. If it is completely filled with samples, or even bottles of water, that variance can be reduced to as little as 3°.
Figure 1 - ArcticTemp Bio/Pharma –23.3 °C freezer from MIDSCI.
Auto-defrost freezers also consume more energy, and air circulation may dry out contents compared to a manual defrost freezer. Very small volume samples will be the most sensitive to temperature spikes in an auto-defrost freezer.
Design improvements in auto-defrost freezers can mitigate the heat spike effects of the defrost cycles. The ArcticTemp Bio/Pharma –23.3 °C freezer from MIDSCI (St. Louis, MO) (Figure 1) is an auto-defrost freezer that uses a large evaporator and coil heater to create shorter defrost cycles. Rather than having coils in the walls, it removes the heat by a forced-air evaporator coil. The defrost system activates on a time schedule, but terminates if the temperature inside the unit deviates from its setting of –23.3 °C.
Lab freezers with manual defrost
In a manual defrost freezer, refrigerant circulates inside the walls of the unit. This creates a stable temperature gradient with the coldest temperature close to the walls and less cold temperatures in the middle. A manual defrost freezer must be turned off for defrosting on a regular schedule. Laboratories that use them must therefore have a backup freezer for storage of contents during defrosting.
Lab freezers for life science laboratories
Life science laboratories are increasingly concerned with energy consumption. A manual defrost freezer is generally more energy-efficient than an auto-defrost model. To conserve energy, purchase a smaller freezer and keep it completely full rather than a large freezer partially full. Choose standard –20 °C freezers over ultralow freezers, and room-temperature or dry storage over frozen storage, wherever possible. Avoid opening the freezer and keep samples organized and clearly labeled so that they can be retrieved and stored quickly.
Figure 2 - 17CAF Freestanding General Purpose Freezer from Marvel Scientific.
The 17CAF Freestanding General Purpose Freezer from Marvel Scientific (Greenville, MI) (Figure 2) is an example of a general-purpose manual defrost freezer for life science applications. It has a 17.1-cubic foot capacity and features adjustable temperature control, automatic door closer, and a basic set of fixed shelves and door shelves for storage.
Explosion-proof lab freezers
Safety is also an important factor in choosing a freezer. Many people do not consider a freezer to be a safety hazard, but sparks from a fan, compressor, or internal light can ignite in the presence of oxygen or volatile chemicals. Freezers that are located in rooms with those substances should be spark-free or explosion-proof.
Terra Universal Inc. (Fullerton, CA) says that its line of explosion-proof freezers by Thermo Fisher Scientific (Waltham, MA) will prevent explosions inside and outside of the unit, even in when hazardous materials are present. Inside the freezers, wiring, splices, the thermostat, relay, and compressor motor are all contained in an enclosure approved for Class 1, Group C, and Group D hazardous environments. In addition, the surface temperature will never exceed the flashpoint of any material in those environments.
Temperature datalogger and alarm system
Temperature datalogging and an alarm are important features for laboratories that are involved in GLP and GMP research activities, and may be a very good idea for other labs. A datalogger and temperature alarm can prevent loss of valuable samples by tracking temperature variations inside the freezer and sounding an alarm if it goes out of a prespecified range. Some systems will also send an alarm e-mail.
Features to look for in a temperature logging and alarm system include Ethernet connectivity, onboard data storage, relay output for an outside security system, and programmable temperature limits and time delay.
Conclusion
In busy laboratories, it is not uncommon for the –20 °C freezer to become outdated or neglected. Freezers that are old, full of frost, or improperly inventoried can result in loss of samples. Freezer alarms that sound when no one is in the laboratory are useless, and should be replaced with systems that trigger a security alarm and “call for help” immediately. Specialized freezers are now available for applications like enzymes and vaccines, and computerized datalogging systems can bring laboratory quality control into the twenty-first century. A freezer may not be the most exciting equipment purchase a laboratory can make, but the peace of mind secure sample storage brings can be very rewarding.
Catherine Shaffer, M.Sc. studied Biological Chemistry at the University of Michigan; e-mail: [email protected].
Please check out our Laboratory Freezer section for more information or to find manufacturers that sell these products.