To keep an ultralow-temperature freezer working for many years, just follow the directions
Keeping biological samples really cold—say, –50 to –80° Celsius—takes an ultralow-temperature (ULT) freezer. At a cost of a few to many thousands of dollars, it’s worth taking care of a ULT freezer from start to finish. By following directions along the way, a ULT freezer can perform accurately for a long, long time.
How long a ULT freezer does its job properly begins at the very beginning. The freezer’s location from the very start impacts how long it lives. Most ultralow-temperature freezers pull air in from the front and release heat from the rear. So, adequate clearance is needed between the freezer and the wall to allow heat to escape. This also means that, to ensure proper air circulation, boxes or spare racks should not be stored on top of the freezer.
With so many makes and models of ULT freezers, though, consult the user’s manual for details on use and maintenance. Reading a few of these starts to remind me of the warning labels on a ladder—a long list that probably arose from more than one person using the device incorrectly. As an example, most ULT freezer user manuals want operators to keep the device safe from exposure, that is, a ULT freezer should not sit out in the rain. Maybe that’s not really shocking, but it could be if that rule is ignored.
Speaking of shocking, all ULTs expect a voltage within a specific range. Each one also gives the range of environmental conditions, such as external temperature, that it can endure. Follow these directions to extend the life and ensure the performance of a ULT. Most of this, though, should be pretty straightforward.
The biggest question
A crucial question is: What should the temperature setting be? There’s no consensus on this—not even close, especially when talking about a specific situation. Instead, scientists are left with something like: Set the temperature as high as it can be and still keep samples safe and improve the odds of long-term performance by the ULT.
So, the best temperature setting depends on the sample. The ongoing debate about –70 versus –80° also shows that energy use comes into the discussion. Here, the ULT’s design also matters. “Setting the temperature to –70 on some freezers will often increase the stress on the engines or compressors. Some newer freezer designs allow for operation at various temperatures by controlling compressor speed. This is coupled with new refrigerants that operate at lower pressures, reducing stress on the freezer motors,” says Joe LaPorte—director product group at Panasonic Healthcare Corporation of North America (Wood Dale, IL).
To select the best temperature setting, look around. Talk to colleagues. Talk to service technicians about what they’ve seen. Don’t just assume that every ULT needs to be set at –80 for the years and years of its life.
Stay cool
For a ULT, cool is not enough. It needs to stay cold, super cold. Don’t expect it to do that on its own. Sure, a new ULT will probably run flawlessly for years with little attention, but don’t count on that.
The “NuAire Ultra Low Temperature Freezer User Manual” even states: “Your ULT unit should be cared for by dedicated personnel.” It adds, “Every 2 to 4 hours, the unit’s working status should be inspected and recorded on a daily basis.”
Part of the regular care includes cleaning. “Taking care of freezers involves actions such as defrosting or removing frost buildup when it is needed, cleaning coils and filters, and keeping door gaskets free of frost or ice so they can make a good seal when the door is closed,” says Kathryn A. Ramirez-Aguilar, University of Colorado Boulder’s green labs program manager. “The CU Green Labs program has put together a preventative maintenance checklist for lab members to use and post on their ULT freezer.” That checklist is freely available at: https://www.colorado.edu/ecenter/sites/default/files/attachedfiles/ult_freezer_basic_maintenance_checklist_with_colors_12162015.pdf.
Regular care can easily extend the life of an ultralow freezer. Frost buildup makes it more difficult for the freezer to maintain ultralow temperatures. Couple that frost with a heavy layer of dust on a freezer’s filters and it’s more difficult to move out heat energy. The net result is greater stress on the compressors and longer running time, which can contribute to a reduced freezer life as well as consuming more energy.
As Ramirez-Aguilar points out, “It is possible for lab members to do the actions described on the checklist themselves.” Also, the CU-Boulder Facilities Management HVAC shop provides free preventative maintenance of campus ULT freezers. With this service, Ramirez-Aguilar explains, “freezers are examined one or more times a year for ice buildup, door gaskets are examined for damages and proper sealing, filters and coils are cleaned, electrical connections are examined, and the amperage of compressors and fans are checked.”
NuAire recommends monthly cleaning. If scientists follow that rule, lab freezers must look a lot different than they did in my day, and so they should! More important, regular cleaning might remind scientists to keep up with other ULT maintenance.
A ULT’s manual will describe an ongoing to-do list. This includes a schedule for cleaning the condenser filter, defrosting and testing as needed. Back to the lists of warnings, one will likely be: Do not take apart the ULT. That is, MacGyvering is not recommended. Instead, call a service technician.
As LaPorte concludes: “Maintenance of the freezer plays a big part not only in its long-term reliability, but also in its performance.” So, here’s to a long life for all ULTs. It’s easy: Just follow the directions.
Mike May is a freelance writer and editor living in Texas. He can be reached at [email protected]