Third-Party Data Shows Stirling Uses Less than Half the Energy in Real Time

You can now view Stirling Ultracold’s ULT Freezers’ energy-efficiency in real time on the CSIRO Freezer Energy Monitoring Dashboard provided by the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia’s national science agency.  With the excellent help of our distribution partner, Bioline, this live feed continually monitors the power output of three ultra-low freezers. This live comparison shows our freezer using significantly less than half the energy of the competitors’ cascade freezers.  Now you don’t need to take our word for it, just go look at the data in real time!

Energy Monitoring Real Time
Full day hourly energy usage average of ULT Freezers. (source: www.energyhive.com)

You’ll note that the Stirling SU780 uses far less power than the other two freezers, even though it’s cooling a larger volume.  In fact, if you compare our 780L freezer (27.5 cu. ft.) with the cascade freezer listed at 386L (13.6 cu. ft.), you can calculate that the Stirling uses about a quarter of the energy per liter.

With a respected governmental research agency now monitoring and sharing this energy comparison data in real time for the world to see, there’s really no reason left to doubt the generous energy and cost savings delivered by Stirling freezers over cascade-compressor models.

Myth #3: Energy Efficiency Compromises Temperature Stability and Uniformity

This is my third blog post addressing the claim that “compromises” must be made when applying energy-efficient technology to ultra-low freezers…

It has been suggested that a cooling system has to be anemic to conserve energy and this will degrade the stability and uniformity of temperatures in the box. This is simply not the case for Stirling Ultracold ultra-low freezers, which offer dramatic energy savings without compromising overall temperature stability or uniformity of temperatures mapped at locations within the freezer cabinet.

Dispelling the Temperature Uniformity Myth
An independent biorepository tested our SU780UE upright ULT freezer by monitoring temperatures at eight specified locations within the cabinet during a 3-hour period after door opening. As shown below, the average temperature difference in the SU780UE varied by only +/- 4.2 °C in this spatial uniformity test:

Stirling Ultracold SU780UE temperature chart

Remarkable Temperature Stability
Over time, it should also be noted that the SU780UE temperature varies by only .2 °C in a steady state because the Stirling engine runs continuously, without stop-start operation. This is in contrast to compressor systems that generate a “sawtooth” temperature profile. As shown (below) in independent tests reported by the same biorepository, temperatures moved up and down around the setpoint when compressors turned on and off during normal operation of a leading brand cascade freezer:

leading cascade freezer temperature variation chart

Industry-Standard “Myth Buster” is Ready and Waiting
Thanks to the new EPA test standard for Ultra-Low Temperature Freezers, temperature uniformity performance can now be presented for “apple to apples’ comparison. The ENERGY STAR® “final test method” requires the mapping of temperatures in various conditions, at specified locations, within the interior compartment. This industry standard should lead to more meaningful evaluations for ULT buyers, once other manufacturers present their compliant test data. Unfortunately, we’re still the only ULT freezer manufacturer who has published EPA-compliant test data, as of this posting.

Myth #2: Energy Efficiency Must Compromise Reliability

This is the second of three blog posts confronting the claim that “compromises” must be made when applying energy-efficient technology to ultra-low freezers . . .

It’s not surprising that an ultra-low freezer technology offering an alternative to decades-old, cascade-compressor technology might create some skepticism when it comes to reliability.  And if that alternative consistently consumes less than half the energy of compressor-powered ULTs, as is the case with Stirling freezers, you might expect those defending the status quo to suggest that energy efficiency comes at a price to system reliability.  This is simply not true and I would like to address this myth . . .

The First Step to Recovery is Admitting There’s a Problem

It is surprising that anyone would suggest that the state of cascade-compressor freezer reliability even remotely resembles a healthy picture. When an executive of a prominent manufacturer once publically stated, “All freezers fail” he was referring to the disappointing failure rates of cascade-compressor freezers.  Many of these manufactures have built high failure rates into their selling narrative so that “redundant capacity” has become a prevailing industry standard.  In fact, cascade-compressor systems not only consume enormous amounts of electric power, but that power produces a significant amount of heat that negatively impacts their reliability.

The Stirling Engine: Two Moving Parts in Continuous, Non-Contact Operation

ULT-reliability-smOn the other hand, our Stirling cooling engine generates less than half the heat and has only two moving parts – a piston and a displacer. These two moving components are supported on gas bearings enabling non-contact operation and, unlike compressors; there is no wear during normal operation of the engine. The engine requires neither oil nor any other form of lubrication. The Stirling piston operates at a fixed frequency by an integral permanent magnet linear motor.  Unlike compressors that operate under stop-start conditions that degrade mechanical reliability, we purposefully designed our engine to run continuously with modulation, so that the damaging effects of current surges are avoided during on-off cycling.

Industry’s Best Standard Warranty

Free-piston Stirling engines of this design have been proven in numerous applications, have flown on the Space Shuttle and continue to cool the instruments on the RHESSI satellite.  More than 6,100 Stirling engines have been incorporated into laboratory equipment, including more than 2,450 ULT freezers operating in over 60 research facilities and institutions. The exceptional quality of the Stirling cooling engine provides the foundation of our 7-year standard warranty with all freezers, because we are willing to stand behind the reliability of our product.

The value of having “been around for a long time” in an industry isn’t what it used to be in these times of technological change.  In fact, that could be the real compromise in an industry marked by decades-old technology and lackluster reliability performance.

Energy Efficiency with No Compromise in ULT Sample Storage Performance

Neill LaneWhenever a new technology comes along promising a “breakthrough” in an established industry, a certain level of healthy skepticism should be expected and even encouraged. If that breakthrough turns out to be proven by data with significant field performance improvements, as is the case with our Stirling engine freezers using less than half the energy of cascade-compressor freezers, this skepticism can be raised to the level of mythology by those who feel the need to defend the status quo.

This is a first of three blog posts that I will be sharing to address several myths being spread about the “compromises” of applying energy efficient technology to ultra-low freezers . . .

Myth Makers Spreading Fear about Energy Efficiency
Some in our industry have suggested that ULT energy efficiency comes at a price that is too great and risks the safety of precious biological samples. This myth was vividly represented to us in a recent email message we saw from a competitor who said, “Since the system is energy efficient, heat removal efficiency and capacity is sacrificed.”

To put it simply, this is not true. The amount of heat that must be removed from a freezer cabinet, at a given temperature, volume and insulation, is the same for everyone. It’s a fact that one unit of heat can be removed by a Stirling engine using less than half the energy of even the best cascade-compressor system. This fact is supported by a recently published report from the Better Buildings Alliance Laboratories, performed for the U.S Department of Energy – who has some authority in these matters. This independent study showed that the Stirling Ultracold freezer saved 66% in energy usage when compared to the average ultra-low freezer, as measured in power consumption per cubic foot.

Some have also suggested that a cooling system has to be anemic to conserve energy and this will sacrifice ULT pull-down and recovery. So let’s tackle that myth by looking at actual data, surveyed from what we believed to be the best competitive ULT freezer on the market . . .

The Pull-Down and Recovery Myth
ULT pull-down comparison chartAgain, it’s simply false to suggest that energy efficiency must come at the expense of temperature pull-down and recovery, as would occur with frequent freezer door openings. Figure 1 shows the pull-down of the Stirling freezer compared with an industry leading cascade system. Pull-down is from an ambient temperature of 25°C ± 2°C with the freezers empty. The Stirling freezer cools to -80°C 18% faster than the cascade system and 34% faster to -86°C. In the case of the cascade system, the cooling system is clearly at the limits of its capability and can only just reach the setpoint. In the case of the Stirling freezer it is clear that the control system intervenes to hold temperature at the setpoint. The Stirling cooling system has the clear capability to go to lower temperatures.

ULT recovery comparison chartFigure 2 shows the recovery from door openings for the Stirling freezer compared with an industry leading cascade system. The inner and outer doors of both freezers are opened for two minutes in this comparison and the ambient is 25°C ± 2°C. Both freezers are empty – the most challenging condition for this test. The Stirling freezer recovers to the -80°C setpoint 29% faster than the cascade freezer.

There’s No Place for Myths with an Industry-Standard Test Method
Now that we have an industry-standard, ENERGY STAR® “final test method” from the EPA, ULT manufacturers can address these issues in a meaningful way, with objective data that provides real answers. It doesn’t serve our industry to put buyers in a position of deciding who to believe, when these questions can be answered by manufacturers presenting their EPA-compliant test data, as we have done.

I find it interesting that the myth makers represent ULT manufacturers who haven’t yet published their standardized test data to the EPA, as of the date of this posting.

Sustainability Rises in Importance at Upcoming ISBER Conference

ISBER logoThe International Society for Biological and Environmental Repositories (ISBER) is the leading professional society for individuals and organizations in the field of biobanking. At its 2015 annual conference in May, ISBER will run a symposium on biorepository financial sustainability through sound business planning. This will continue the discussion on financial sustainability in biobanking that started in 2014, which supported the creation of the sustainability grant opportunity by Conversant BIO that was announced this month.  The outcome of the grant opportunity will be a part of the larger symposium on business models for sustainability.

For this upcoming symposium, we have submitted an abstract to discuss the EPA’s new, industry-standard test method and share our EPA-compliant energy consumption test results for the Stirling SU780UE upright freezer. These results support our published specs, which have shown that Stirling freezers use less than half the energy of comparable, cascade-compressor ULTs. With the significant energy cost savings and reduced carbon-footprint achieved by using our freezers, both financial and sustainability benefits are attainable for biorepositories, which is a major focus of the upcoming ISBER conference.

For more details on the EPA’s ENERGY STAR standard for ULT freezers and why it’s important for organizations in the biobanking field, review our blog post.


If you’re attending the ISBER 2015 annual conference May 5-9 in Phoenix, you are invited to visit the Stirling Ultracold exhibit (booth #217) to see a demonstration of our ULT freezers.

Helping Research Organizations Move from HFC’s to Natural Refrigerants

Following up my last post about university campuses adopting sustainable strategies for ultra-low temp freezers, this post highlights how research organizations are making significant strides toward carbon-neutrality by using Stirling Ultracold ULTs with natural refrigerants . . .

As we also announced in our June 2014 press release, New -80C High Efficiency Ultra-Low Freezer Uses 100% Natural Refrigerants, the 27.5 cu. ft. SU780UE upright freezer uses about 10 grams of helium in its Stirling engine and about 90 grams of ethane in the thermosiphon.  The freezer is UL listed for safe hydrocarbon refrigerant use and the EPA’s Significant New Alternatives Policy Program (SNAP) has allowed Stirling Ultracold to sell freezers containing ethane in the U.S.

Although no other ULT freezer for sale in the United States offers 100% natural refrigerants in its cooling system, these refrigerants have been used as a replacement to HCFC’s and HFC’s outside the U.S. for many years.  In contrast, a typical ultra-low freezer using HFC refrigerants in its cooling system has a net effect that is up to 17,000 times more damaging to the ozone layer than the natural refrigerants used in the Model SU780UE cooling system.  Most surprising is the superior performance that natural refrigerants can also bring to ULT storage when properly applied.

ATMO logoThe adoption of Stirling freezers is becoming a part of corporate and institutional sustainability programs that are targeting conversion to hydrocarbon-based, natural refrigerants systems used in U.S. research facilities.  You can see an example of this on the ATMOsphere website, which features a presentation, entitled “Campus Conversion to Climate Friendly Refrigerants”.

Combining usage of natural refrigerants and the Stirling engine, which uses less than half the energy of cascade-compressors, the overall carbon footprint of a Stirling Ultracold SU780UE upright freezer is less than half that of any competing product. Research organizations are discovering the sizable sustainability gains that are possible, simply by replacing multiple ULT freezers running 24/7/365 in their laboratory facilities.

We’re pleased to see the progress that these research organizations are making toward sustainability and the use of natural refrigerants . . . and we’re very happy that our freezers have become a part of it!

Article Shares How Stirling is Helping Universities Achieve Sustainability Goals

We like spreading the word about the significant help our ULT freezers offer to research organizations and institutions pursuing sustainability goals . . . and it’s very encouraging when we find others who are talking about it, too. My next couple of posts will give a shout-out to some third parties and users of our products who are telling the Stirling sustainability story better than we can . . .

The Chilling Effect
ULT energy usage problemIn her article The Chilling Effect, Emily Byrd recently shared the challenges of Green Labs, a University of North Carolina committee devoted to bringing together students, staff and faculty interested in waste reduction and efficiency in labs on campus. Byrd writes about Green Labs’ latest initiative, the “National Freezer Challenge”, which is a multi-university competition that aims to improve sustainability in research facilities by changing how scientists use ultra-low temperature freezers. Efforts like the National Freezer Challenge are essential to raising consciousness about ULT freezers and energy use.

When people understand this issue they are so much more likely to seek solutions. This article shares a great example of this fact by pointing to a study of nine UNC campus buildings. The study concluded that the Genetic Medicine Building consumed more energy than the other eight combined because it houses more than 100 ultra-low temperature freezers.

Ms. Byrd’s article also refers to Duke University’s sustainability program and the success achieved by turning to Stirling Ultracold freezers. Citing Randy Smith, head of Duke’s Green Labs Committee . . .

“We bought a Stirling to test it, and it just blew our minds, really. There’s a lot of money to be saved when it comes to these freezers, and now Stirlings are the only new ones we’re allowed to plug in.”

It is gratifying to see UNC making progress on this issue and I appreciate Emily Byrd for publishing her account of the process. The word is getting out!

EPA’s New Industry Standard for ULT Energy Testing – Why it’s So Important

Neill LaneWe’re thrilled to share our new “ULTra Insights” blog with you and look forward to posting on a number of relevant subjects relating to lab energy management, sustainability, ULT technology and research freezer requirements.  I’m especially excited that our very first post is about such an important topic for our industry – energy testing standards.

For a few years now, we’ve stood by our claims of 50-60% energy savings with the free-piston Stirling engine cooled freezers, but all our competitors also claim that their ultra-low freezers are energy efficient.  Laying claim to “energy efficiency” in our industry, up until recently, has always been a matter of murky interpretation.  That’s because there hasn’t been an industry-wide standard for testing energy consumption of ULTs.  Now we have that standard thanks to the EPA!

Why Do We Need Another EPA Standard?
If we use one method for testing our freezers’ under certain conditions and other manufacturers use different testing methods/conditions, it becomes impossible for ULT buyers to compare “apples to apples” when it comes to energy consumption of our units.  To use an analogy, who’s to say that a new Toyota Prius really uses less gas than Lincoln Town Car if there is no EPA standard for testing miles per gallon?  Of course there is an EPA testing standard for automobile MPGs and we don’t question which car gets better gas mileage.  More importantly, we confidently know the quantitative difference in MPGs, which allows us to calculate fuel cost savings for the Prius.

Now we’re very happy to report that the EPA has collaborated with manufacturers to publish an agreed-upon industry standard for testing the energy consumption of ultra-low freezers.  You can actually go to the EPA’s ENERGY STAR® website and read this published standard for yourself.  This is a big deal for buyers of ultra-low freezers.

Why is a Testing Standard So Important to Ultra-Low Freezer Buyers?
Considering that current model cascade-compressor, ultra-low freezers consume the equivalent electric power of an average U.S. household; a clear metric for comparing energy consumption of models has significant financial implications for research facilities, many of which have 100s or 1000s of ULTs running 24/7.  With this new testing standard, there’s a real potential for ULT buyers to compare “apples to apples” for the first time, and be better informed when assessing freezer cost of ownership, sustainability and energy management, based on meaningful data.

Stirling Ultracold Energy Consumption Test Data is Already Available, but  . . .
Of course, this testing standard will only be meaningful if ultra-low freezer manufacturers publically share EPA-standard data for comparable models.  That’s why we have released standardized energy consumption test results for our model SU780UE ultra-low freezer, in response to the EPA’s request for data.  We recently announced this in our press release, Stirling Ultracold First to Submit Ultra-Low Freezer Test Data to the EPA.  (If you would to see full documentation of our “Stirling Ultracold Model SU780UE Ultra Low Temperature Freezer Test Results”, please contact Stirling Ultracold Sales.

The release of this test data complied with the EPA-published standard final test method and indicated that the energy consumption of our upright ultra-low freezer was 7.97 kWh/day over the steady-state period of the test and 9.24 kWh/day over the complete 24-hour test.

These results have confirmed our published specs and we now look forward to settling any doubts about our stated 50-60% energy savings compared to cascade-compressor ULTs, as other manufacturers submit their own industry-standard test data.  If you’re a buyer or specifier of ultra-low freezers, you should look forward to seeing their data, too.