ULT freezers represent some of the most energy-demanding pieces of laboratory equipment available and are ubiquitous in virtually every laboratory environment. When new, ULT freezers operating at their standard set points of -70°C or -80°C consume approximately 16 to 22 kilowatt hours (kWh) per day. After years of service this amount may climb to over 30 kWh per day, an amount in excess of the energy usage of the average American home according to the U.S. Energy Information Administration. For large organizations and academic institutions that may have thousands of freezers on-site, operational costs can be astonishing and even marginal improvements in efficiency can have substantial return.
When considering laboratory cold storage needs, researchers require short- and long-term sample storage solutions that maintain both reliable storage conditions and accurate temperature control. For many lab managers, however, minimizing both energy consumption and operating costs is of primary importance. Fortunately, through simple best practices for cold storage coupled with manufacturer-driven innovations in design and compressor technology, enormous savings can quickly be realized.
A place for everything
Keeping your ULT freezer organized can be a challenge. However, consider that for every minute an upright ULT freezer door is open, it takes approximately 10 minutes for the freezer to recover to its set point. If your inventory is organized, you will greatly reduce the running time of your freezer and minimize the risks of compromising valuable samples by exposing them to fluctuating temperatures. There are several options available to assist in sample organization, including customized racking options, secondary storage containment, and electronic inventory systems that utilize bar codes or radio frequency identification. Software inventory control systems such as RURO’s FreezerPro software may also assist in tracking samples both in and out of your freezer while streamlining workflow and identifying old or unneeded samples that should be disposed of. For researchers who desire a fully automated solution, systems such as SmartFreezer by Angelantoni Industrie combine inventory management software with a fully robotic vial retrieval system. These systems have the ability to store thousands of samples and retrieve them quickly without the risk of accidental handling mishaps and without compromising the temperature of the containment area.
Keeping your ULT freezer properly filled can also keep operating costs down. Freezers that are too bare have little thermal mass and also may lose cold air rapidly when the door is open. This can be remedied by filling empty space with frozen gel packs or bottles full of ice. Conversely, freezers that are overfilled may lead to wide temperature variations due to passive natural convection potentially damaging sensitive samples. Keeping an accurate inventory and properly disposing of unneeded samples will keep your freezer operating at peak efficiency.
Choosing the right size of ULT freezer for your lab may not be as simple as it seems. While smaller freezers would seem to be more efficient, in fact, small ULT freezer units operate with much higher intensity (energy consumption per cubic foot) than larger freezers do. This is owing to smaller freezers having a larger surface-to-volume ratio, coupled with the fact that smaller compressor motors are less electrically efficient and smaller compressors are less mechanically efficient than larger ones. Considering that a small 3 cu. ft. ULT freezer may operate with intensity up to 600 percent greater than a comparable larger model, it is advisable to purchase freezers with capacities of 20 cu. ft. or larger to maximize energy efficiency within the laboratory environment. If your laboratory needs are not so great as to require a full-size freezer, you may consider sharing resources with another lab and gaining some valuable floor space.
In considering size, you should also examine the sample sizes you are working with. If you are storing 0.5 mL samples using 2 mL screw-top vials, your storage is not particularly efficient. In this case, lab managers may wish to encourage or subsidize the use of micro-vials and 96-well plates. These are readily available from most distributors and can increase your sample storage capacity by nearly 60 percent.
Out with the cold, in with new
One of the fastest ways to achieve cost and energy savings is through the retirement of old or outdated ULT freezers. Technological improvements in compressor design, insulation, and cabinet design have resulted in considerable improvements in sample storage efficiencies. Be aware, however, that freezer efficiency will decrease over time owing to inadequate maintenance, seal degradation, coolant loss, mechanical failure, and degraded lubricants. In many cases, unmaintained ULT freezers may be drawing up to four times as much power as a newer or well-maintained freezer. These freezers are often neglected, sitting in hallways, and filled with unneeded or forgotten samples. Regular testing of your lab’s freezers will quickly identify those in need of repair or retirement. In addition, regular maintenance is highly recommended for your cold storage equipment if you want it to age gracefully. While many small repairs, when performed early, may be relatively cheap to service, if you wait too long you may be faced with an expensive compressor rebuild or replacement.
If you are engaged in a new build, it might be advisable to consider process cooling with a chilled water loop. Ultra-low temperature freezer manufacturers (such as Panasonic) that offer optional water cooling within their cascade cooling cycle can offer dramatic savings and reduced ecological footprint for your lab. Such systems operate by removing heat from the condenser across a heat exchanger and channeling it out of the system through exiting water. This translates into less heat generation by the freezer unit, allowing for substantial savings in air-conditioning costs for the laboratory. Further, the extracted heat can be used elsewhere in the lab for water or environmental heating systems.
To properly manage your cold storage needs, it is necessary to plan for the future. Consider involving your lab in the development of a plan toward continuous improvement. This may mean developing a freezer rebate program to assist with the retirement of aging equipment or creating incentives to clean out existing space. In addition, seek expert advice from manufacturers when purchasing and maintaining equipment that is energy efficient and offers long-term investment benefits. Finally, make certain you engage all the key stakeholders in developing a management plan for your ULT storage needs; small contributions from everyone involved can amount to substantial overall savings.
For additional resources on cold storage, including useful articles and a list of manufacturers, visit www.labmanager.com/cold-storage