Given the cost of purchasing and running an ultralow temperature (ULT) freezer, as well as the importance of the precious samples they hold, properly maintaining this key piece of equipment is absolutely critical.
Key problems that can occur in ULT freezers and how to avoid them
Scott Masiella, director of product management at ULT freezer manufacturer Stirling Ultracold, identifies three main issues that can arise with these products: infrastructure constraints, excessive heat, and power supply challenges.
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1. Infrastructure constraints
Infrastructure challenges can include everything from floor space constraints to heating, ventilation, and air conditioning (HVAC) issues. Because freezers need adequate ventilation to run properly, users also need to ensure there is adequate space around the unit for proper airflow and access, which may present further challenges to those with limited space.
Depending on which model they purchase, users may require several inches of clearance around the freezer for proper airflow. However there are models available with a higher storage density that take up less space and that direct the heat they generate in such a way that users can position the unit directly against the wall. The higher energy efficiency of new models can also help manage many HVAC challenges.
Masiella adds that it’s important that users fully understand the conditions of the location where the freezer will be operated, as these units are designed to be used in locations with controlled humidity and temperature on flat, level, and stable surfaces.
2. Excessive heat
“All ULT models produce heat as a by-product of ultracold temperature production,” Masiella explains. “The more ULTs running in a facility, such as a biobank in a central warehouse, the more heat that builds up within the building interior.” High temperatures in the location where the ULT freezers are kept can have a big impact on their performance, he adds, meaning that HVAC systems need to work harder, resulting in higher energy costs and the possibility of freezer failures.
To prevent such issues, users need to make sure they know the ambient temperature operating range of the freezer models they are looking to purchase, so that the freezers’ location is kept within this range. According to documentation ULT freezer manufacturer Thermo Fisher Scientific provides with its freezers, “the ambient condition needs to be controlled between 15°C (59°F) and 32°C (90°F).”
Choosing a ULT freezer that is ENERGY STAR®-certified helps mitigate temperature-related issues as well, since such energy-efficient models produce less heat than those that do not have this certification.
3. Power supply challenges
As Masiella points out, depending on where in the world your lab is located, the high-voltage/ current power outlets necessary to run ULT freezers in your facility may have numerous power supply requirements. To avoid any issues caused by power supply challenges, Masiella recommends careful planning of ULT freezer power options and purchasing ULT freezers that have universal power built in and a wide voltage range. “By merely changing power cords, these models can automatically switch across voltages, including standard outlets from 110 to 240 volts,” he says.
Important steps to looking after your ULT freezer
According to materials provided to Lab Manager from a presentation by Dr. Alex Esmon, senior director, SBS GM Cold Storage Laboratory Products Division, Thermo Fisher Scientific, there are a few ways to ensure your ULT freezer is running at top performance:
- Keep the number of door openings to a minimum and ensure doors are kept open only as long as necessary
- Only open the inner doors that you need to open
- Keep samples close together, or “consolidate cargo”
- Keep a close eye on the unit display to ensure you stay on top of any temperature fluctuations, etc.
If you don’t have the time or experience necessary, and you’re storing particularly critical samples, Esmon notes it may be worth purchasing a maintenance contract for your freezers to ensure they’re always running at top performance. For those storing COVID-19 vaccines, many ULT companies have specialized service and support plans.
A few other ULT housekeeping tasks Esmon mentions are to consider the need to restrict access to the freezer and to make sure you enable the unit’s remote connectivity options. Such options could include connecting to an administrator’s smartphone or other device so the lab is notified right away if something is out of spec.
For long-term ULT freezer care, Esmon and Masiella’s tips include:
- Read and follow the user manual
- Keep filters, vents, and fans clean
- Ensure you regularly remove frost from gaskets and shelves
- Consider purchasing an extended warranty or service plan if your samples are irreplaceable
- Select a monitoring system that meets your needs
- Ensure your ULT service provider’s contact info is always close at hand
- Ensure proper door alignment and prevent ice buildup on a regular basis
- Defrost or de-ice freezers at least once a year
“Given the extreme temperature of ULT freezers, they often form ice on the gasket and around doors,” Masiella explains. “If not regularly cleared, ice buildup can prohibit the door from closing properly and allow outside air to enter the cabinet. Ice can also lead to damage to the door latch and door alignment.”
Ensuring proper sample storage in a ULT freezer
Both Masiella and Esmon highlight the importance of having a storage plan in place before users start their ULT freezers. Users should set up the shelves and racks in the required configuration in advance and document where samples/material will go beforehand, so that they don’t have to keep the freezer doors open for long periods searching for samples. Establishing proper sample management and tracking practices in advance is also critical to prevent this same issue.
“The longer the door is open, the warmer the samples inside will become, and the longer the freezer will take to return to the desired storage temperature,” Masiella says.
Before loading a ULT freezer, Esmon says that it should be run at the set temperature for at least 12 hours, and, once it’s ready to go, the unit should be loaded one shelf at a time, starting from the top shelf.
For better energy efficiency, a lower carbon footprint, and lower energy costs, users may want to consider using high-density racks and boxes to store samples, Masiella says, a practice also recommended by My Green Lab, an organization dedicated to increasing laboratory sustainability.
ULT freezer monitoring systems
All ULTs have some sort of monitoring system built in, but users can upgrade to more advanced options, offered by either the original manufacturer or third-party companies. When choosing a more advanced monitoring system, Masiella suggests users look for a system that includes cloud accessibility via remote devices for automatic temperature and temperature alarm monitoring as well as 21 CFR Part 11 and EN12830-2018 compliance for good manufacturing practice.
In terms of looking after their ULT freezer monitoring system, Masiella says users should re-calibrate the sensors used “to integrated electronics after extended use,” adding that “some systems have simplified the calibration procedure by using a sensor hot swapping process.”
By following a few key steps before turning on their ULT freezers, and some important housekeeping recommendations afterward, laboratory professionals can ensure these units have a long and happy life in the lab and that their samples are protected.
