The display on your -80℃, -20℃, or 4℃ cold storage units will almost always say just that - -80℃, -20℃, or +4℃. However, it is not uncommon for discrepancies between the temperature reported on your freezer and lab monitoring systems to arise. For instance, a freezer in the lab will display -80℃, however the monitoring solution reflects -75℃. This blog highlights how fluctuations in freezer temperature are common and other considerations to keep in mind for properly monitoring freezers in R&D labs.
Most freezers and refrigerators have a compressor (or compressors) that cool the unit. The compressor runs when the temperature gets too high, and turns off once the temperature has gotten low enough. The freezer insulation keeps the temperature from rising quickly, even when the compressor is off.
Uniformity generally refers to a state of consistency. In this context, we’re interested in temperature uniformity throughout different locations in the freezer. When analyzing temperature uniformity, temperature readings over time are averaged. Variation due to compressor cycles is not taken into account because while this affects temperature over time, it should affect all locations in the freezers in a consistent way.
In an ideal world, a ULT freezer averages -80℃ on all sides and in the middle. However, in reality, it might be -75℃ at the top, -78℃ at the side, and -82℃ in the middle. The University of California Riverside published a study in 2016 evaluating ULT freezer temperature uniformity and is very helpful in understanding what the temperature distribution can look like.
Image below is a figure from that study which illustrates a typical temperature profile:
Two common reasons why there may be a lack of uniformity in freezers being monitored could be:
Common factors include:
There are two key take-aways to keep in mind when working with freezers in the lab and how to appropriately monitor them for your business needs:
Takeaway 1: If precise temperature matters to your samples, understand the spots in your equipment with variable temperatures and advise scientists appropriately. If you’ve ever accidentally frozen a dozen eggs because you put them on the wrong shelf in your refrigerator at home - the same problem can happen in the lab.
Takeaway 2: For installation and maintenance of your lab monitoring system, be aware of how probe placement might affect the temperature data collected. If you are a TetraScience Lab Monitoring customer, read on for specifics. If not, request a demo to find out how the solution can streamline freezer monitoring in your lab.
Overall, freezer temperature uniformity should not affect the day-to-day usage of your alarm system. Your alert thresholds should be set above the highest average temperature typically seen in your freezer during normal operation.
Understanding temperature distribution is more important during installation or if you need to move, reposition, or replace the temperature probe.
If you are doing self-installation you should be aware of these temperature differences, and take the following steps to minimize issues due to normal temperature variation:
Keep in mind that every model of freezer is different! If you think the temperature you’re recording is too high or low on average, you can always try moving the probe to a different location.
The key takeaway here is not to panic when there is a difference in how temperature reflects when monitoring freezers in R&D life science labs! Fluctuations in the temperature and discrepancies reflected between the freezers and monitoring systems do not equate failure in either system. Knowing these intricacies can help alleviate worry, establish appropriate alert set points to eliminate alert fatigue, and generally bring peace of mind to scientists and lab managers. The key is to employ solutions that are built and battle-tested to support best-practices for how important lab equipment is not only used, but also properly monitored.