There are a lot of factors to consider when shopping for an ultra-low temperature freezer. Below we're going to explore a few of the most vital things to keep in mind when looking for a ULT freezer, new or used.
Capacity is undoubtedly one of the most vital factors by which to shop for freezers. Freezers come in a huge range of sizes, all the way from small benchtop models that barely break 28 liters to massive units that can hold nearly 1,000 liters. Most freezers on the used market hover between 500 and 700 liters. You'll need to have an idea of how much space your lab's samples will require, then you can start shopping around for ULTs in that range.
If you're at all familiar with ULT freezers, you'll know that they come in two configurations: upright and chest. Each configuration has its advantages and drawbacks, but for most labs, upright freezers are the most appropriate options. In fact, upright units make up over 95% of all ULT freezer sales. There are two reasons for this: (1) they take up much less floor space than chest freezers and (2) are much more convenient to use. If your lab, like virtually all others, is running low on free space then an upright freezer would be the best option for you.
That said, there are cases in which a chest freezer would be prudent. If you (1) have enough space to accommodate one and (2) don't intend on opening it very frequently, then a chest freezer is a great option. Their orientation makes them more efficient and allows them to recover to set temperatures after being opened faster than upright units.
Data collection is one of the main aspects in which ULT freezers have vastly improved over the years. The earliest models contained only chart recorders that manually graphed the temperature on a circular sheet of paper. Nowadays, chart recorders are all but obsolete thanks to the spread of digital data collection, onboard software to view records, and USB exporting. Chart recorders are still included simply for the sake of redundancy.
A useful rule of thumb is that the more critical your samples are, the more sophisticated your freezer's data logging system should be. With higher-end systems come more onboard storage, higher-resolution records, and other features that may prove essential to scientists with critical samples.
For those on the other end of the spectrum, who have no need for records of any kind, there are ULT freezers without any data logging at all. Opting for one of those is a good way for such buyers to save costs.
ULT freezers must use two compressors in a configuration called "cascade refrigeration" to reach the temperatures they do. While highly effective, cascade refrigeration setups require a lot of power. In fact, most of them require 220V power outlets -- something that not all facilities are equipped with. If your facility only has 110V outlets, you'll have to purchase a power converter as well.
It's recommended that you keep each of your freezers on a dedicated power outlet. Putting anything more than a single freezer on an outlet can easily flip a breaker.
Last but not least, it's important to keep logistics in mind. Many ULT freezers won't fit through standard doorframes. You'll need to keep your facility's doorframes, room size, etc. in mind when picking one out. Furthermore, according to biocompare.com, ULT freezers need at least half a foot on all sides for proper circulation, so their total footprint is considerably larger than just their dimensions. Take a freezer with a 9 sq. ft. footprint, for instance. Accounting for a 6 inch buffer on all sides of it brings that total footprint to 16 sq. ft. — a 77% increase!
Additionally, paying to ship a ULT freezer is not cheap. You should expect to pay between $700 and $1,000 for shipping if you buy from an auction. Purchasing from a dedicated lab equipment dealer is generally a few hundred dollars cheaper.
(If You're Buying Used) Age
Freezers are built to last. Oftentimes, buying a used freezer that's several years old can still yield a great ROI. But no freezer lasts forever. Here are a few things to keep in mind so you don't buy a unit that dies sooner rather than later:
Firstly, if a listing doesn't indicate whether the seller ever actually tested the freezer, don't even consider buying it. Ideally, there should be photos showing the freezer's temperature reading at -86°C, or at least some temperature sufficient for your samples.
Secondly, it's wise to consider your timeframe. If you only need a ULT temporarily, you could likely get by with one that's 10+ years old. No need to buy a freezer that still has another 10 years of life in it if you only need it for 1 year.