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There are several types of laboratory freezers and applications. For example, ultralow-temperature (ULT) freezers with temperatures ranging from –20 °C to –86 °C are designed to meet the cold storage needs of critical samples such as blood and biological samples (see Figure 1). If storing reagents, the packaging indicates at what temperature they should be stored. A general freezer may be appropriate depending on the temperature range. Less frequently, stock chemicals may also require freezer storage. When looking for a lab freezer, consider the factors below to help optimize cold storage needs. Ultimately, a laboratory’s specific protocol and application will dictate the type of freezer and temperature range necessary for storage.
Figure 1 – StableTemp –86 °C ultralow-temperature upright freezer (Cole-Parmer, Vernon Hills, IL).Space requirements
Capacity is an important factor in selection and is usually determined by the amount of racks or boxes a freezer can hold (see Figures 2 and 3). Use of freezer storage boxes and racks helps with organizing a freezer, making it easier to store and retrieve items. Do not discount these items when looking for a freezer, as they optimize freezer space.
Figure 2 – Colored cardboard freezer boxes (Argos Technologies).
Figure 3 – PolarSafe 100-Place EPS microtube racks (Argos Technologies).It is important to find the optimal location for the freezer. When floor space is not readily available, undercounter units are a good option. If the freezer needs to be installed in a hazardous zone, choose an explosion-proof model appropriate for the environment and certified with the necessary ratings. Under no circumstances should space in a laboratory freezer be taken up with food or lunchboxes.
Installation location and environmental conditions
The exact requirements for the installation will depend on the specifications, which should be listed in the freezer’s manual. Most units cannot exceed a specific elevation from sea level or cannot be used in high ambient temperatures. Humidity levels in the lab must also be within the freezer’s capabilities. Without adhering to the environmental specifications, the unit will not work properly and will never reach the desired temperature setpoint. Also, the freezer must be operated indoors, as rain can produce a significant risk of electrical shock or fire. The ideal location will have no direct sunlight, be well-ventilated, be situated away from any other heat-producing equipment, and be placed as far as possible from any walls or items indicated in the freezer’s manual. It is best to consult with the factory to make sure the freezer will fit the intended environment.
Auto and manual defrost options
A freezer with auto defrost will save time but also consume more energy. It may also give less stable temperature uniformity as the defrost cycles. If temperature stability is important, choose a manual defrost model. A manual defrost freezer should ideally be defrosted once a month or whenever ice builds up on the gasket of the freezer door. If ice does form on the gasket, there will be a gap that allows air in through the door, disrupting temperature performance. To defrost, make sure the unit is unplugged, and have a temporary storage solution in place for items that need to be stored during the defrost. Then, keep the freezer open for a few hours and let the unit defrost. Accelerate the process by scraping ice away with a plastic scrapper. Make sure the freezer is completely defrosted and wipe up any water left inside. Also, make sure no water remains on the floor or under the unit. Plug the unit back in and power it on until it reaches the desired temperature.
Temperature monitoring and data loggers
Many freezers are now outfitted with high and low alarms, and many laboratories have also started using data loggers to continually monitor freezer conditions to avoid losing critical samples. These loggers can contact the user by phone or e-mail to alert them of an alarm or possible power outage (see Figure 4). Other freezer monitoring features include backup cooling systems that use carbon dioxide and ambient temperature alarms.
Figure 4 – Digi-Sense traceable data-logging refrigerator/freezer thermometers with TraceableLIVE wireless capability and calibration (Cole-Parmer).Calibration
Many freezers are either factory calibrated or calibrated by a calibration service. Some freezers can also be calibrated onsite with the use of a calibrated thermometer, and then changing the offset temperature of the freezer until the freezer display reads the same temperature indicated on the thermometer. A freezer should be calibrated as frequently as the standard operating procedure (SOP) indicates, but usually once a year is sufficient.
Cleaning
Clean a freezer at the frequency stated in the manual; once a month is standard. Clear any dust on, around, and inside the freezer. Use the cleaning agent suggested in the manual, but typically a neutral detergent is all that is required. Check the condenser filter to see it is cleaned once a month, or if the model has a condenser alarm, whenever that is activated. Typically, the condenser filter can be washed with water, completely dried, and then reinstalled. However, there are instances where the filter needs to be replaced. (Note: Before cleaning, make sure the freezer is unplugged to avoid electrical shock.)
Maintenance
The amount of maintenance required depends on many factors, and these are outlined in the freezer’s manual. In units with a backup battery for alarms, the batteries may need to replaced every few years. Some parts might be considered consumables or require lubrication. It depends on the manufacturer. If an alarm is activated, best practice is to consult the manual for the proper remedy. Some repairs may need to be handled by a trained professional. Onsite repair is the preferred method.
Disposal
Many different states and agencies have rules dictating the appropriate way to dispose of a freezer, especially older models. Consult local government agencies to legally and appropriately dispose of the freezer to avoid fines and safety hazards.
Summary
A laboratory freezer is one of the most expensive purchases for a laboratory. Reviewing best practices and following the steps outlined in the freezer’s manual can provide optimal storage of valuable samples for many years.
Michael Steinert is product marketing manager, BioSciences, Cole-Parmer, 625 East Bunker Ct., Vernon Hills, IL 60061, U.S.A.; tel.: 847-549-7600; e-mail: [email protected]; www.coleparmer.com