Buying and Maintaining an Ultralow Temperature Freezer

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September 05, 2019

With a typical service life between 12 and 15 years, it is not often that you need to purchase an ultralow temperature (ULT) freezer, but when you do, you will want to make sure it has all the features necessary to protect the integrity of your samples, is a good fit for your lab, and operates efficiently.

Types of ULT freezers

There are many factors to consider and decisions to make before you buy an ULT freezer. Among the first will be if you want a chest or upright freezer. Chest freezers are more efficient and last longer than uprights. Temperature set points are often reached more quickly, and they are easier to maintain. That said, the footprint of a chest freezer is an issue with space-constrained labs, and less than 5% of ULT freezers sold are chest style, according to Nuaire.

Refrigerants

Reduced energy consumption is among the benefits of using hydrocarbon refrigerants, which have been the industry standard since CFCs were banned. Hydrocarbon refrigerants also enable more efficient refrigeration systems that dissipate less heat to their surroundings and can reduce the air conditioning requirement in many labs. Green refrigerants R170 (Ethane) and R290 (Propane) are increasingly touted as even more efficient options; however, these highly efficient refrigerants are potentially flammable and their use is often restricted.

Temperature regulation

Once you set up your freezer, you will likely want to cool it down from room temperature to the set temperature quickly so that you can start using it. However, pull-down time can range from 9 to 26 hours, according to a 2016 analysis from University of California, Riverside. Pull-down time can be impacted by the refrigerant used, the type of insulation, the efficiency of the compressor, as well as the positioning of shelves in the freezer.

Warm-up time is the time it takes to reach ambient temperature from –80°C. This data will be important in case of power outage or freezer malfunction. The UC Riverside analysis found that if the power was cut and the freezer door remained closed, it took about 9 hours for samples to reach –50°C and two days for samples to reach 0°C in all three of the freezers that were evaluated. Many manufacturers provide data on how their systems compare to others regarding pull-down, warm-up, and power consumption. You should ask to see this data.

Twin compressors, innovative door gasket designs, and a slew of insulation options (including foam as well as foam combined with vacuum insulation panels) all help maintain temperature and ensure energy efficiency. Make sure to carefully review the specifications for the freezers you are considering to determine if these innovative features are worth the additional expense.

Temperature uniformity

You should also request data on temperature variation inside the ULT freezer from vendors you are considering. When looking at the test data, make sure to find out about the location of the testing probes and how loaded the freezer was during testing. The UC Riverside group found variability in temperature in all three freezers it studied, with the warmest spots typically at the top part of the freezer, especially along the door.

Capacity

Balancing your capacity needs, or anticipated storage volume, and space realities can be tricky. The internal storage volume of an ULT freezer can range from 200 L to 800 L, with larger capacity freezers, not surprisingly, having larger footprints. Labs with limited space often need to consider smaller freezers, though energy consumption per cubic foot is higher for small freezers when compared to large freezers. To manage an abundance of samples, large labs typically have multiple freezers and keep them in specially designed freezer farms.

In order to meet your storage demands, an assortment of racks, storage boxes, as well as freezer boxes is available. Make sure the accessories you select are designed to withstand ultra-low temperatures.

Location, location, location

Where you plan to put the freezer should be decided upon before beginning the purchasing process. Obviously, the freezer you purchase must fit in the provided space, but it also needs to make it from your loading dock, through your lab doors, and to its preferred location.

ULT freezers can generate a considerable amount of heat and noise. As a result, adequate ventilation is critical. A minimum space of 203 mm on top and clearance of 127 mm on both sides and the back is recommended. In addition, some models are noisier than others, so if your freezer will be located in or near a quiet area, you should ask vendors about their freezers’ decibel ratings.

Preventive maintenance

There are a number of steps you can take to keep your freezer in tip-top shape, which will help ensure optimal performance as well as minimize energy consumption.

Frost and ice buildup is inevitable with ULT freezers. To stay on top of the buildup, inspect the door seals and gaskets every time you open the freezer. Scrape away any accumulated ice every few weeks at a minimum, and wipe down the gaskets with a soft cloth at least once a month. Dust build-up is also unavoidable, but it must be addressed, as dust accumulation on the condenser filter can compromise its performance. Dust around your freezers regularly, cleaning condenser filters every two to three months and the condenser coil at least once a year.

Monitoring

Many freezers come with dedicated alarm and back-up systems to alert users to sub-optimal operating conditions including high temperature, power failure, and open door. According to Nuaire, alarms in and of themselves are not enough to prevent catastrophes. All labs should have a plan in place to deal with problems, and each freezer should be labeled with point-of-contact details and information on an alternative unit if samples need to be moved.

24/7 Monitoring Systems Provide Peace of Mind and More
Although most freezers come with alarms these days, the alarm systems from freezer manufacturers can be simplistic. Companies like Elemental Machines provide more robust systems that are often used to supplement existing systems.
“In many cases, the alarm from the freezer manufacturer just sounds in the laboratory or manufacturing environment,” explains Sridhar Iyengar, Ph.D., Founder/CEO of Elemental Machines. “Our alarms are nearly infinitely configurable. It is one thing to set a local alarm when a reading goes out of specification and hope there is someone in the lab to hear it. It is quite another to send an alarm via text to a variety of team members reliably, 24/7, through power outages, internet outages, etc.”
The Element-T from Elemental collects temperature readings every 15 seconds, which, with a little effort, can tell you more than just the temperature inside. You can monitor the compressor cycles of the freezer and see when the compressor is on or off. If a compressor is working too hard, the freezer may need to be defrosted, or it may be failing.
Another thing you can tell is when the door is opened and how long it remains open. “This information can be used to understand utilization,” Iyengar says. “If you have a freezer farm of 100 freezers, are they all being used or are there some that are never opened? Could you save money by decommissioning some of these freezers? We did a study with one of our customers to find out. They found two freezers that were never opened over a two-month period.”
The Element-T can be used in newer as well as older freezers. It is wireless, battery-operated, and requires no mounting screws. It has a magnet inside that is typically used to affix it to any freezer or fridge. It automatically connects via Bluetooth to the portable gateway and starts sending data to the Elemental Cloud within a minute. The thermocouple is placed inside the freezer or fridge to be monitored. The thermocouple wire is very thin (~500 microns), so it does not interfere with the door opening or closing, nor does it interfere with the door seal. According to Iyengar, a typical installation takes less than a minute.