The Costs of Mechanical Ultra-Low Temperature Freezers

ULT sample storage freezers are a crucial component of a number of laboratories, biobanks, and clinics across the globe. These units enable the medium to long-term storage of various biological samples for example cell extracts, proteins, RNA, or DNA.

While sample storage freezers are found everywhere, they are normally not considered until they are necessary or worse, until they have malfunctioned. This means that a number of researchers may not be aware of the environmental impact and energy costs of their freezer.

How Much Does it Cost to Run an Ultra-Low freezer?

The upright mechanical or ‘minus 80’ freezer is one of the most commonly used types of storage freezer. Frequently referred to as a ‘ULT’ or an ‘ultra-low freezer’, they are similar in design to household freezers. They normally utilise a refrigerant like propane (R290) or ethane (R170) to function and are powered by motors or compressors.

A fixed temperature of -20 °C or -40 °C can be maintained by a standard upright mechanical freezer, but the majority will run at approximately -80 °C. Mechanical freezers can maintain lower temperatures than this, but it can cause significant strain on the motor and may result in failures.

To maintain temperatures as low as this, a consistent power supply is necessary. Phil Wirdzek, the President and Executive Director of the International Institute for Sustainable Laboratories, explained that the traditional ULT freezer utilises approximately 20 kWh of energy per day, the same amount of energy as a single-family home.

The energy and running costs can quickly add up, considering that research facilities and laboratories normally run dozens, if not hundreds, of these freezers at once.

An upright, mechanical ULT freezer can vary in average running costs from £570 ($750) to £750 ($1000) each year according to a number of factors. Frequent upkeep and maintenance through defrosting can decrease this expense, but not significantly.

These prices do not account for the extra expense of the removal of warm air and HVAC systems. This can increase the cost even more and is a serious consideration for storage facilities and laboratories that have a limited budget. A significant environmental impact is also caused by constant energy usage.

Turning Up the Heat

Elevating the temperature is a well-known solution to the environmental and financial expenses of ULT freezers.

Many supporters of cheaper, smarter ULT freezers state that there is no need for them to run at such a low temperature. They argue that various kinds of samples can remain viable at -70 °C, and that raising the temperature by just 10 °C can prove to be effective.

Many argue that even -80 °C is not low enough for the long term storage of delicate samples as this is still much higher than the glass transition point of water (-135 °C), the boundary at which essentially all biological functions cease. This is the only method of defense against the natural degradation of cells for the most crucial samples.

An alternative to this substantial power usage and environmental concern may be to decrease the temperature.

Getting Colder

LN2 travels through a heat exchange system in a variable temperature nitrogen vapor freezer, where the freezer is cooled by the vaporization energy of the LN2. Consistent temperatures from -20 to -150 °C can be achieved with just a 5 °C change in temperature variance from top to bottom.

This makes sure that even the most delicate cells are protected by decreasing the speed of biological functions to a crawl, far beyond the abilities of the majority of upright freezers.

Contemporary nitrogen vapor freezers, like the MVE Variō™, need a fraction of the mechanical units’ energy. In standard use conditions, the power consumption is only 8 W per day or approximately 1% of an upright freezer’s usage.

A lack of power will not harm the integrity of stored samples due to the optional battery backup which can manage all critical functions. Nitrogen vapor sample freezers could in theory store frozen samples indefinitely, as long as the LN2 supply is maintained.

There are also no extra HVAC requirements because of the negative thermal load, and no HFC or CFC refrigerants. In comparison to a conventional compressor or mechanical freezers, LN₂ sample freezers are beneficial for both the environment and financial constraints.

With an enhanced focus from the scientific and biomedical community on decreasing environmental impact, it may be the time for more researchers to change from a mechanical to a nitrogen vapor sample freezer.

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Last updated: Jul 1, 2020 at 2:48 AM

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