Trying to keep biological samples extremely cold—say, –50 to –80° Celsius—takes an ultralow-temperature (ULT) freezer. As we know, ultra-low temperature (ULT) freezers are specifically made to work between -86°C and -45°C, but they often work at a set temperature of -70°C or -80°C. These freezers can last for about 12 to 15 years.

What is an Ultra Low Temperature freezer (ULT Freezer)?

Ultra Low Temperature freezers are designed for storage of biological materials such virus, bacteria, eukaryotic cells, blood and semen.  These freezers are used in blood banks, hospitals, epidemic prevention services, research institutes, and biomedical engineering facilities.They play a critical role in maintaining the integrity of biomedical samples and some vaccines.

There is a variety of available styles and sizes available when it comes to low and ultra-low freezers. Choices include chest-style, upright, and under the counter styles. Sizes range from five to 49 cubic feet. The temperature range for an ultra-low freezer is -45°C to -86°C .

• There are two basic types of ULT freezers —upright freezers and chest freezers. The latter is more efficient than the former, but is generally not preferred because of usual space limitations. In fact, chest style freezers account for less than 5% of ULT freezer sales. Yet, these freezers have a longer service because they have an efficient design which requires only minimum usage of compressor. The same efficiency makes it possible to reach temperature set points more rapidly and this is maintained continuously.
• The twin ULT freezer equipped with separate compressors is a popular option. Dual compressor systems cycle high stage and low stage refrigerants to maintain a set point temperature. If a compressor fails a ULT freezer will have a hard time maintaining set point temperature. Back-up systems are available to maintain set point until a repair is done. Dual compressors help separate the work load needed to maintain the system and prevent oil logging..ULT freezers equipped with vacuum insulated panel lining provides a good option for space-constrained environments. These freezers come with more capacity and have a small footprint. Owing to the lower thermal conductivity of a partial vacuum, a VIP panel is generally thinner compared to the traditional foam insulation required to obtain the same level of thermal insulating properties. The integrity of the VIP panels should be protected. Temperature fluctuations can cause cracks, which can affect the partial vacuum conditions and thus reduce the insulating properties. Cracks can also occur in the insulation and lead to failures if there is frequent opening and closing of door of a VIP insulated freezer.
• Two compressors is yet another ULT freezer option. In majority of freezers, twin compressors do not work as backups. These are independent compressors, with one functioning as a high stage compressor device that cools down the temperature of low stage condenser. However, this is an expensive option and is yet to become a standard option in the industry. Despite this fact, some manufacturers justify the high price in view of improved performance.

Refrigeration systems can be a single high-power compressor hermetically sealed or two cascade compressors. The two cascade solution, is two refrigeration circuits connected so that the evaporator of one cools the condenser of the other, facilitating the condensation of the compressed gas in the first circuit.

Air-cooled condensers are generally used in laboratory refrigeration systems. They consist of tubular batteries (copper or copper-aluminium) arranged to provide as much surface heat transfer as possible. In Ultra freezers, the circulation of the cooling air is forced by an engine driven fan and the expansion of the refrigerant fluids is obtained by capillary tubes.

Evaporation takes place through steel plate heat exchangers, located inside the chamber, or by means of a coil. In chest freezers, the copper or copper-aluminium coil evaporator is placed along the walls and bottom, while in the upright freezers it runs along the walls and at the top. The coil in the cabinet eliminates the efficiency issue in the heat exchange of freezers with the coil in the insulation cavity.

Refrigerant fluids used in the ULT freezers

• After CFC’s were banned, ULT freezers switched to HCFC refrigerants. Currently, freezers which are the most energy efficient use hydrocarbon refrigerants (HFCs).
• The ULT freezer industry is trending towards using highly efficient, but flammable, refrigerants such as R170 Ethane, and R270 Propane. The United States and France do not yet allow flammable refrigerants despite the many years both have been in use elsewhere. ULT freezers using flammable refrigerants are popular in the European pharmacy industry, but not yet available in the United States due to regulatory  restrictions. ULT freezers using flammable refrigerants are 50% more energy efficient than models using conventional refrigerants after pull down, and have decreased potential for oil logging.

Which accessories can an Ultra Freezer have?

The accessories generally supplied include:

a CO2 and/or LN2 emergency system (both with independent power supply, probe and battery).

To track room temperature, freezers are optionally equipped with a charted weekly temperature recorder, which have almost completely been replaced by digital ones.

In line with current international standards, the recorder is mandatory for freezers at -45° C and -86° C for the storage of blood plasma.

Other accessories include: various kinds of steel containers, drawers and racks for storage of cryoboxes, microplates, blood plasma and test tubes designed for low and very low temperature storage.

Handling goods inside the ultra freezers requires you to wear suitable protective headgear, leather gloves to protect your hands, overalls and smocks.

How Long does it take for ULT Freezers to Cool?

• The pull down time is the time it takes to get to -80°C after set-up or installation. After a power failure, the time it takes to reach -60°C is called the holdover time.
• After a door opens ULT freezers are designed to recover the temperature as soon as possible. Every time an upright ULT freezer door is opened it takes 10 minutes to recover its
• temperature back to its setpoint.
• Flammable refrigerant gas helps pull down faster, and saves around 15% electricity.
• Warm up can be slowed down by having effective insulation, door gaskets, and a claw door. All three are important.
• Quality manufacturers supply graphs to show how their systems compare to others with data on pull down, heating up, power consumption. Pull down and warmup numbers vary widely, with some systems taking 3 times as long as others. Be aware of the location inside the freezer where temperature was measured in the manufacturers’ data, as pull down times measured in the middle of a chamber can vary considerably versus measuring at the top or bottom.

Ultra-low temperature freezers find wide application in:

• research universities
• medical centers and hospitals
• blood banks
• forensic labs for long-term evidence storage
• establishing performance specs for parts used in extreme cold environments

As to more specific examples of the above, ultra-low temperature freezers are used to store biological samples such as DNA/RNA, plant samples and insect artifacts, autopsy materials, blood, plasma and tissues, chemicals, drugs and antibiotics.

Manufacturing firms and performance testing labs use ultra-low temperature freezers to determine the ability of products and machinery to perform reliably under severe low temperature conditions such as found in Arctic and Antarctic regions.

These myriad applications suggest that ultra-low temperature freezers may house multiple and different experiments, some of which may require frequent checking while others remain undisturbed for lengthy periods of time. And in fact if they do, this becomes a feature that can be applied to your selection process.

The function and life of an ultralow-temperature (ULT) freezer depend on proper usage and preven- tive maintenance. Some elements of proper use  start at the very beginning of ownership and others last until a ULT’s  last days. However,  getting them  all right ensures getting the best performance from start to finish.

Some of the keys steps to using a ULT the correct way only take minimal effort. Part of that is knowing the right steps. “Having a checklist is a good thing   to do,” says Buckner Richardson, Vice President of In- ternational Sales at NuAire. Those steps should lead a lab manager to use a ULT as designed, and it all begins with where it goes.

Freezer location

Proper usage starts with  the  placement  of  a  ULT  in a lab. If the room is hotter than 90°F (32°C), it is much too hot for a ULT. “This happens in laboratories without air conditioning,” says Richardson, “and the freezer cannot breathe.”

Respectable ULT manufacturers  test  how  much heat a ULT can endure. “The manufacturer puts an air-cooled ULT in a room at 110°F (43°C) and tracks performance until the freezer fails,” says Richardson. “NuAire has had one such an occurrence with a ULT operating in a high temperature environment for a year, but they are designed for no hotter than 90°F (32°C).”

Despite the guidelines that go with any ULT, buyers still put some of the units in the improper location. When it comes to placing a ULT where it’s too hot, Richardson says, “that is a common mistake.”

The temperature is one part of placement, but there is more. If there is more than one ULT in a room, it creates even more heat, and the ULTs need space  for ventilation. That means following the manufac- turer’s guidelines for spacing. NuAire, for example, recommends clearance of 8 inches (203 millimeters) above a ULT and 5 inches (127 millimeters) on the sides and back. The NuAire guidelines add: “Avoid side by side spacing unless a ULT  freezer is located  in a specially designed freezer farm. There should be no storage on top of a ULT freezer.”

If the options for placing a ULT cannot meet the envi- ronmental requirements, water-cooled condensers may be added. That can overcome some of the con- straints. Even then, as many placement guidelines as possible should be followed. At the very least, a lab manager should keep a ULT out of direct sunlight.

Still, there are other aspects of proper use to consider.

Intended use

When asked about some of the most common errors in using a ULT, Richardson says, “One big mistake that we’ve seen in the field is deliberate abuse.” By that, he means using a ULT as a flash or blast freez- er. “Sometimes, a blood bank, for example, wants to freeze plasma of cryoprecipitate as quickly as pos- sible,” Richardson explains. “Someone takes some- thing at room temperature or warmer and puts it in a ULT, when he or she requires a blast freezer.”

If someone needs a blast freezer, that is what he or she should acquire. The use of a -80°C ULT as a blast freezer damages the ULT. “What goes in a ULT should be frozen,” Richardson says. “If you load a ULT full of warm samples and expect them to be rapidly frozen, you can get away with that for a while, but eventual- ly, the ULT wears out.” He adds, “It’s a fairly common event we have noticed.”

Even though a high-performance ULT can handle a limited number of unfrozen samples, that doesn’t make it a good idea. In general, a best practice is to avoid placing warm samples in a ULT.

As Richardson points out, “You can break a com- pressor in a few years by abusing a ULT.” As a re- minder, he adds: “A −80° freezer is to store samples essentially indefinitely.”

Electrical source

To maximize the life of a ULT, there’s another element of use to keep in mind—the plug. A manufacturer will note the proper power for a ULT. For example, most ULTs  operate around 220 volts at 60 hertz on   a 15Amp, single-phase circuit. NuAire guidelines state that “some customers need 115V with 20Amp single-phase circuits. Very few freezers can maintain even -57°C at 115V and 15Amp, the exception being small, low interior volume freezers.”

To take advantage of a ULT’s potential,  samples  must also be placed appropriately inside. “We have found a large number of laboratories use the racks they have, which do not appropriately fit the freez- er resulting in lost storage space,” Richardson notes. “Spend the money on the right shelves to fully utilize the freezer.”

Used to store precious, often irreplaceable samples, ultralow-temperature (ULT) freezers are an essential workhorse of laboratories worldwide. When used and maintained properly these specialist units typically provide 10–12 years of highly reliable service, but to get the best out of them it is important that they are treated with respect. This includes locating them wisely, ensuring they are provided with a power supply of the correct voltage, and performing essential preventive maintenance functions to keep them running optimally. We spoke with Adam Christensen, technical support/service trainer at NuAire, who shared with us his expertise in ULT freezer preventive maintenance.

“For maximum performance and efficiency, it’s recommended that a ULT freezer is checked and calibrated periodically by a qualified service technician,” he says. “However, regular cleaning and maintenance is relatively straightforward and can easily be performed by the end users. We suggest adopting a number of simple practices to extend freezer life. By making these routine it’s possible to detect and correct any potential sources of failure in timely and efficient manner.”

Minimize frost or ice build-up

“Although gradual formation of frost or ice within the inner chamber is inevitable, this can be kept to a minimum,” explains Christensen. “The room in which the unit is situated should have an ambient temperature no higher than 32^oC, while exposure to direct sunlight and drafts or heating/cooling vents should be avoided. It’s also important to provide suitable spacing around the unit for effective ventilation.”

Further steps to lessen frost or ice build-up include minimizing the number and duration of door openings and checking that the door latches securely upon closure. “Periodic removal of frost or ice build-up from the door gaskets and inner chamber can be achieved by scraping,” notes Christensen. “The vacuum relief port should also be cleared regularly.”

Defrost the chamber regularly

“We recommend fully defrosting the chamber at least twice a year depending on usage and environmental conditions,” says Christensen. “This involves transferring all contents to another ULT freezer, switching off the unit, then wiping it out with a non‐chloride detergent once it has defrosted. This can be a good time to inspect door gaskets and make sure they seal properly, to clear out old stock, and to re-organize existing samples to maintain correct airflow and afford better accessibility. The unit should then be allowed to operate empty overnight before being reloaded.”

Keep the condenser clean

By transferring heat from inside the ULT freezer to outside, the condenser has one of the most important roles to play in ULT storage. Christensen explains that dust accumulation on the condenser filter can compromise its performance, adding that the condenser coil also requires regular preventive maintenance. “We suggest cleaning the condenser filter every two to three months, more frequently if the environment is particularly dusty, and the condenser coil at least once a year,” he notes.

Wipe down the door gaskets

“If frost and ice build-up isn’t removed from the inner and outer door gaskets, they can tear,” says Christensen. “This compromises the performance of the unit. Leaks are usually indicated by a streak of frost at the point of gasket failure, but by wiping down the gaskets with a soft cloth at least once a month, tearing can be avoided. Furthermore, frost and ice build-up around gasketing can wear out the outer door latch since it makes it hard to close the door.”

Understand freezer alarms

ULT freezers are often fitted with alarms to indicate a variety of sub-optimal operating conditions. These can include high temperature, power failure, low battery life, prolonged door opening, and system monitoring failure. According to Christensen, knowing what the different alarms mean facilitates swift remedial action. “It is imperative that alarms are not ignored and that a plan of action is in place for situations that require operator input. This includes labeling each freezer clearly with the details of a point of contact and back-up contact and having spare ULT freezer space available should there be a need to transfer samples to an alternative unit.”

Freezer alarms will still occur during a power outage since the display and buzzer are powered by a battery. Christensen says this should be replaced by a certified technician every 2.5 years, when the battery timer will also be reset. “The battery life of NuAire freezer alarms can be checked by entering the function code menu, however it is sufficient to simply have the battery replaced once the 2.5 years expires and the light is illuminated,” he adds. “Checking the battery timer in the function menu can be incorporated into routine cleaning and maintenance schedules to provide end users with additional peace of mind.”

A wide range of ULT freezers are available, yet they all have one thing in common—they require care and attention to keep them performing at their best. Just a few simple preventive maintenance steps will ensure the longevity of sample material while maximizing the lifetime of these vital pieces of equipment.

•  Sample Safety

ULT freezers have been designed with sample safety as their priority. When labs use faulty equipment, thousands of dollars’ worth of specimens can be destroyed. ULT freezers provide temperature stability in the internal chambers, which preserve the most valuable samples.

Keeping specimens intact provides staff with peace of mind. Most freezer models are equipped with a seven-point contact silicone gasket, which prevents heat leaks. Also, this feature will preserve the specimens in a power failure. Additionally, ULT freezers are designed to quickly recover the low temperatures after the doors have been opened. Modern lab freezers will ensure your stored samples remain in stable condition.

• Energy Efficiency

• More Size Options

Ultra-Low temperature freezers are sold by a variety of manufacturers in different models. No matter your storage needs, there are several ULT freezers to choose from to find the perfect fit for your lab. For a lab with a large volume of specimens and frequent use, an upright ultra-low temperature freezer permits easy access. Moreover, upright freezers have adjustable inner shelves and compartments, and usually cool much faster after it’s been opened.

There are also medium-sized “chest” ULT freezers. These freezers guarantee safe, long-term storage for samples. Chest-sized ultra-low temperature freezers are perfect for labs that don’t need to remove samples from storage on a frequent basis.

ULT freezers come in even more compact options. For a smaller volume of materials, you can select a tabletop or under-bench model. Before choosing a size, take your clinic’s specimen intake into account. While most ULT freezers feature adjustable shelving and removable pieces, it’s important to ensure your freezer will meet your storage needs.

• Keep Your Samples Secure

Keeping your samples secure is highly important. Most of the ultra-low temperature freezers on the market come with a range of security features. Security features are vital for a ULT freezer with many users.

There are ULT freezers available that can only be accessed with an authorized keycard. With some, an alarm feature can be activated that will alert staff of an unauthorized user.

Some freezers even have fingerprint scanning, which guarantees your samples will not be compromised.

When you have precious samples to protect, sometimes an Ultra-Low Temperature (ULT) freezer is an absolute requirement. Whether it’s the first time you’re buying one or you have to replace an old unit, there are several important factors to consider. These units are understandably far pricier than regular freezers, and you need to know you’re getting the very best freezer for your needs.Here we’ll look closely at the factors you need to consider when purchasing a ULT freezer.

Capacity

Of course, one of the most important features is how much a freezer can hold. All of our ULT freezers come in a range of sizes.

You also need to decide if you want a chest freezer or an upright freezer. An upright freezer is more convenient in terms of accessibility, so may be preferred if you need to frequently access samples. However, upright freezers are a little less efficient as during door openings, the cold air is more likely to escape, due to the tendency of colder air to flow downwards. As such, if accessibility is less of an issue, such as with long-term storage, you may want to go with a chest freezer.

The choice may also depend on the space you’re working with as the footprint of a chest freezer will be larger than that of an upright freezer with the same capacity. When considering how much space you have available to house the freezer, you need to account for ample room for ventilation. A suggested minimum clearance is 5” at the back and sides and 8” on top of freezer.

While the size and shape is important, so is the way in which samples may be stored. For example, having adjustable (or at least removable) shelves is a plus as it gives you flexibility in what size samples you can store and helps you utilize space better. It’s also important to note what size racks the unit can hold and how readily available these are. For example, So-Low offers a range of racks for upright and chest ULT freezers.

Cooldown Time

When it comes to cooldown time, there are two main parameters to consider. It’s helpful to know the pulldown time, which is how long the freezer takes to get to its setpoint temperature after installation or setup. Secondly, you’ll want to consider how quickly the freezer will return to its setpoint temperature after a door opening. This is especially important if you anticipate frequent door openings.

Another important factor is how long the freezer will stay within a given temperature range in case of a power failure. After all, you need to know how long you have before your samples are compromised. Some manufacturers will be able to send you graphs showing such temperature data.

Backup Systems

Speaking of power failures, it’s prudent to look at whether or not backup systems are available for a given unit. For example, there’s an automatic backup system available for So-Low freezers that uses CO2 or LN2 to lower the temperature of the freezer if it reaches a specific temperature.

American BioTech (ABS) Supply Ultra Low Temperature Freezers come with a battery backup for electronics (such as alarms and controls) during power outages.

Temperature Stability or Differential

Most ULT freezers have a set temperature differential which indicates how far the actual temperature might deviate from the setpoint temperature. The reason for this is to give the compressor a break between cycles. This decreases wear on the compressor, extending the lifespan of the freezer.

You may want to know how much the temperature might vary from the setpoint at various points across the chamber. Knowing the minimum and maximum temperatures can help you decide if the freezer is even suitable for your application, and if so, what an appropriate setpoint temperature is to ensure the integrity of your samples (by guaranteeing they’ll be kept at a particular minimum temperature).

For example, if the maximum temperature is 2°C above the setpoint and you need your samples to be at a maximum of -70°C, then the setpoint temperature should be at least as low -72°C.

Some units enable you to set the temperature stability yourself. For example, ABS Ultra Low Temperature Freezers are typically set to +/-5°C (the range can be set by the factory or the user). The manufacturer does recommend not setting the differential any tighter than +/-3°C as the rapid cycling will increase wear on the compressors and decrease compressor life.

Alarm System

Temperature deviations can spell disaster for your samples, so you want to know if anything has gone awry. Having sufficient warning systems in place can give you chance to address the issue before it’s too late.

Some units come with visible and audible alarms that signal things like temperature fluctuation or power failure. For example, freezers in the So-Low ULT range, such as the So-Low Ultra Low Mini-Freezers (below left), have audible and visual alarms that signal when there is an electrical or mechanical failure.

The alarm on the So-Low Platinum Series Ultra Low Freezer (above right) also has an over and under-temperature setting.

Running Costs

According to a 2014 US Department of Energy report, at the time of the study, a 25 cu ft. -80oC freezer used around 20 kWh per day, which is about the same amount of energy as a small house. However, that was five years ago and advances in compressor design, better insulation, and improved cabinet organization have enabled manufacturers to improve the efficiency of ULT freezers.

That being said, energy costs remain high, so it’s important to look at the financial impact of running a ULT freezer, especially if you plan on purchasing multiple units. According to a 2016 report by the University of California Riverside Office of Sustainability, an average new unit consumes 17 kWh per day. In contrast, an energy-efficient unit consumes on average 8.86 kWh per day. This ties in with Energy Star’s listings, with the most efficient ULT freezer on the list consuming around 7.52 kWh per day.

Aside from looking at energy consumption, it’s a good idea to look out for key features that will improve the efficiency of a unit, such as double-walled doors and additional insulation in critical areas.

Voltage Requirements

A ULT freezer is a powerful machine so it’s worth checking the required voltage and wiring conditions for a given unit. The larger an ultra-low freezer is, the more likely that it will only be available in higher voltages.

There may also be potential issues with voltage fluctuations, especially if your lab is in an older building. If the voltage is too high, it could cause failure of components due to overheating. Too low a voltage increases the amperage which can again lead to overheating. In either case, the lifespan of the machine will be reduced.

Some manufacturers will provide a recommended maximum voltage fluctuation, for example, 10% of the nominal voltage. Certain units come with features that overcome voltage issues such as a voltage stabilizer for fluctuating voltages or a voltage booster for low line voltages. The latter is a feature of the ABS Ultra Low Temperature Freezers

Warranty Options

As with any expensive piece of equipment, you’ll likely want a guarantee that you’re not going to have to spend money on repairs, at least in the short term. Most manufacturers offer at least a one-year warranty as standard, and some have option to pay for an extended warranty.

In So-Low’s case, the initial 12-month warranty comes with your purchase and includes parts and labor (including compressor issues). An optional extended warranty can be applied to the compressor for up to four years (five years in total from the purchase date), although this doesn’t cover labor costs.

With American BioTech Supply, units typically come with a two-year parts and labor warranty and a three-year compressor parts warranty.