Freezer physics: when flexibility fights stability

29 October 2025 Tags: freezer freezer layout temperature monitoring temperature stability

Following the recent freezer disaster, I settled on a replacement from Labcold. The price is not dissimilar to the Liebherr model, but the technicians in our teaching lab have told me that they have a lot of Biocold freezers, and that, other than the necessity of regular defrosting, they never had a failed unit—and they go in and out of these freezers a lot. SLS provided me with a quote very quickly, Labcold confirmed availability and estimated delivery date, and the delivery was executed by the most professional delivery team I have experienced in a while.

Cooling systems: a tale of two technologies

Straight away I noticed one major difference. The older Liebherr model has "cooled shelves", which are fixed. The Labcold model uses a fan-based cooling system, and the advantage is that the layout of the interior is much more flexible. For example, to fit our cryo boxes I bought a relatively expensive metal racking system that allows storage of 3 × 2 boxes. However, when the Liebherr freezer came in 2 1/2 years ago, the frames were too high for the fixed shelves of the Liebherr, so I had to retire them intermittently and had to buy new racks for 2 × 2 boxes, which then wasted quite a bit of space. I was rather pleasantly surprised that the flexible shelving system of the Labcold model means that I can now use a combination of the old and new racks, making the use of the interior much more efficient.

The empty freezer cooled down quite rapidly to the pre-set temperature of -20°C. Once fully loaded, our internal temperature probe reported an internal temperature around -19°C, but that can be easily adjusted. All in all, the new freezer seems to work well.

The physics of cold air (and the price of flexibility)

However, the better flexibility also comes with a significant downside: once opened, even if briefly, the temperature drops very significantly. Without the cooled shelves that keep the freezer cool, the heavier cold air simply drops out of the bottom. The temperature probe confirms that this is not just registered by the freezer-internal probe, but by the probe in liquid as well. The time of keeping the freezer open has to be kept at a minimum, which is somewhat frustrating, because the main purpose of the freezer is to hold stocks of strains. With more efficient racking we have some space, but we cannot store consumables in the freezer, because going in and out means more temperature variations than with the Liebherr model. It also means that the temperature variations when the freezer is closed are indeed larger than with the Liebherr model.

The bottom line

It is quite important to consider purpose, layout, and other parameters of these larger pieces of lab equipment before purchase so that a fully informed decision can be made. Each cooling technology comes with its own trade-offs: cooled shelves offer superior temperature stability at the cost of inflexibility, while fan-based systems provide adaptability but demand disciplined access protocols. In the end, there's no universal "best" freezer – only the best freezer for your specific application.