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How Ultra-Low Temperature Free-Piston Freezers Can Protect Your Research

Ultra-Low Temperature Free-Piston Freezers

Having a reliable ultra-low temperature (ULT) freezer in your research laboratory not only stores research samples safely but also protects fragile specimens from degradation during an unexpected power outage. A power outage or a refrigeration system failure can put years of specimen samples in jeopardy.

In 2012, during Hurricane Sandy, researchers at the New York University (NYU) School of Medicine lost electrical infrastructure to their research laboratory which cut off supply to their freezers. Despite their valiant efforts carrying samples on dry ice down 18 flights of stairs, the extended power outage destroyed 25 years of specimens contained in their freezers [1].

When the Stirling engine has no power to operate, the thermosiphon stops working which generates 50% less heat in the interior of the freezer than older style cascade compressor ULT freezers [2]. As the freezer warms up slowly, researchers have significantly more time to find or repair back-up systems or alternative freezers before research samples are destroyed or rendered unusable.

Stirling freezers have no current surge associated with start-up of the freezers and a backup alarm that can alert the laboratory when there is an energy failure. When the system is back on a steady operation, the temperature remains constant within less than half a degree of the set point.

Current ULT freezers have similar cascade or auto-cascade compressor cooling technology. However, the Stirling freezer does not use cascade compressors to keep the inside freezer at or below minus 800C refrigeration.

The unique ULT freezer is a combination of an electrically driven free-piston Stirling engine and a thermosiphon that cools the system more energy efficiently. By taking advantage of the latest ULT freezer technology, you can safeguard research hours invested in collecting and storing samples and thousands of dollars in funding grants.

How Stirling Freezer Technology Works

Unlike cascade compressor ULT freezers, the Stirling freezer technology is driven by a free-piston engine with two moving parts supported by non-contact gas bearings.

The Stirling engine cold head is connected to a thermosiphon that contains the cooling medium (refrigerant) and wraps around the cabinet interior. No oil or other form of lubrication is used in the engine so oil clogging in the tubes doesn't restrict the flow of the refrigerant.

The ULT free-piston freezer offers the highest density per square foot of floor space of any freezer on the market. The upright freezers configuration means they can be placed on the floor for easy access and the cooling engine and electronics is housed in a mechanical compartment at the top of the freezer and is not exposed to spillage.

Energy Savings & Maintenance Costs

Conventional cascade compressors can have as many as 24 moving parts which are expected to fail one or more times over the life of the freezer and can be costly to repair.

However, the free-piston engine Stirling ULT freezer uses no life-limiting bearings and seals and there are no moving parts or valves in the thermosiphon.

Research laboratory testing has found the full size 780-litre Stirling ULT freezer is more energy efficient than other ULT freezers, using between 41% and 49% of the energy of cascade freezers at minus 800C [2].

Additionally, due to its lower energy use during operation, Stirling freezers produce less carbon dioxide than a cascade freezer during its manufacture and operation leaving a smaller carbon footprint [2].

In the event of freezer engine failure, the standard seven-year warranty offered is longer than the best available five-year warranty offered on cascade compressors.

The Stirling cooling engine technology offers fundamental technology and field proven reliability benefits over cascade compressors, delivering peace of mind to research laboratories in protecting valuable research.

To find out more about Stirling Ultracold freezers or to speak to one of our friendly and experience technicians, please contact us via our online contact form.


[1] Zolia-Pazner, S. Saving Specimens After Sandy, NEJM 2013; 368: e27.

[2] Lane, N. Ultra-Low Temperature Free Piston Stirling Engine Freezers (Whitepaper) 2013 Stirling Ultra-cold.

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