Cryogenic storage: liquid nitrogen or mechanical freezer?

17 April 2024

In short, cryogenic storage is all storage that takes place below -130°C degrees. In fact, it has been proven that at a temperature of -130°C degrees or colder, all living organisms come to a standstill. Below this temperature, the aging process stops and cells can be stored indefinitely. The most well-known forms of cryogenic storage are: liquid nitrogen and mechanical freezers. But what are the advantages and disadvantages of these forms and what options are available? Together with our director Robert van der Kuijlen we discuss these options so that our customer can make the best choice.

Greater safety margin with liquid nitrogen

Liquid nitrogen (here in after referred to as LN2) has been used for cryogenic storage for many years. In the liquid phase, this form offers a uniform temperature of -196°C. This means that the temperature remains stable over an extended period of time. Robert adds: ''This temperature of -196°C gives users confidence in storing their precious research. In fact, should something fail or the LN2 supplier is temporarily unable to deliver, it will take some time for the temperature to reach -130°C. Without opening the lid, the samples still remain safe for several days.''

Store in liquid or vapor phase?

It is commonly chosen to store samples in the liquid phase due to the certainty of -196°C, which provides a greater safety margin. Robert: ''However, keep in mind that more LN2 is consumed in the liquid phase because more evaporation occurs when removing a rack. We have seen in recent years that more and more customers are choosing to store their samples in the vapor phase.''

A 1995 article wrote about the possibility of cross-contamination in the liquid phase. ''Because of this, more and more people are choosing vapor phase storage instead of fully immersing the samples in LN2. In the former case, any possibility of cross-contamination is eliminated, but the safety margin is reduced in case the LN2 supplier is temporarily unable to supply,'' Robert mentions.

Difference between automatic and manual filling of LN2

In cryogenic storage in LN2, we distinguish between automatic and manual filling. In the case of automatically filled tanks, a system automatically replenishes the LN2 vessel. In the case of manually filled vessels, it is up to the user to replenish the vessel himself.

Manually filled storage vessels have a smaller neck opening. The small neck opening makes the LN2 less likely to evaporate because the static evaporation rate is reduced. Automatically filled tanks are more convenient and offer much greater storage space. They do consume more liquid nitrogen due to the larger neck openings and pre-cooling of lines during automatic replenishment.

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Automatically Manually

Assure safety

It is common knowledge that liquid nitrogen is dangerous to work with. In addition, LN2 has the property of evaporating even if the container is sealed airtight. Also, LN2 extracts oxygen from the air. ''You cannot smell it, you cannot taste it, you cannot see it, but if you're working and the oxygen level is too low, it becomes dangerous. So being alert to this is important,'' Robert says. ''The area where the LN2 is located should also have O2-meters. As an additional safety measure, it is recommended that there is always someone outside the room watching the user, in case the alarm in that room does not go off.''

Due to the constant evaporation of LN2, it also remains a continuous process to refill the LN2 vessels. As a result, LN2 must be purchased and budgeted on a consistent basis. Robert: ''Liquid nitrogen certainly provides a greater margin of safety in temperature. So one has to take into account the cost aspect, safety aspect and the fact that liquid nitrogen is not as user-friendly.''

Mechanical cryogenic freezers as alternative

Ensuring the safety of lab technicians is important, and some organizations want to get rid of liquid nitrogen for that reason. As an alternative, we offer a -150°C mechanical cryogenic freezer. First, the freezer provides a nice uniform temperature of -150°C. That means a safety margin of 20°C in case of a power failure, for example. Robert adds, ''With liquid nitrogen, the user can store in the vapor phase, but this comes at the expense of storage space. With mechanical cooling, this does not apply. Therefore, the 200 liters available can be fully utilized by the user for the samples. Also, getting material in and out is easier with our -150°C freezer than with a LN2 vessel. This is because the freezer is only one meter high and therefore user-friendly.''

Furthermore, a cryogenic freezer is safer because there is no liquid nitrogen involved. Robert: ''After installing the cryogenic freezer(s) in the room, it is important to ensure that the ambient temperature is correct. Despite the fact that our -150°C freezer is energy efficient, heat dissipation must be taken into account. As a result, it is important that the room is properly conditioned. This will affect the power consumption. Finally, the freezer produces a noise level around 55 dB.''

View our solid -150°C cryogenic freezer with good storage space from our own brand Labselect:

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Precautions for cryogenic freezers

Should the freezer fail, for example, due to a power outage, the freezer will start to heat up slowly. Robert: ''Should the freezer fail, for whatever reason, I always recommend being prepared for this. First, I recommend connecting the freezer to the building’s emergency generator. Second, to connect a LN2 backup system to the freezer. In the event of a failure, LN2, in vapor form, can be injected into the freezer to keep the material below the critical temperature of -130°C. This does require a LN2 fill tank to be ready with LN2.''

Calculating the Total Cost of Ownership
Robert concludes: ''We offer both options at Poly Temp so whether a LN2 storage tank is needed or a mechanical freezer, it is entirely up to the customer. Both systems offer cryogenic temperatures for storage of valuable samples.

We do recommend that a longer-term TCO calculation be done and factored into the final decision.

The calculation compares these forms of cryogenic storage. Liquid nitrogen requires a specially equipped room and supply of nitrogen, compared to our cryogenic freezer with power costs and climate control systems. Of course it is possible to present the issue to us and we are happy to do the calculation together with our customer.''

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