Top five things to consider when preparing to purchase freezers for research labs

Top five things to consider when preparing to purchase freezers for research labs

By Selene Colon

Research laboratories require reliable and efficient freezers to store various samples, including biological specimens, enzymes, antibodies, and other temperature-sensitive reagents. Second only to fume hoods, your lab’s cold storage (refrigerators, freezers, cold rooms) is likely the next-biggest category of energy consumers in your lab space.

One way to reduce the energy consumption from your lab is adjusting your use and reliance on energy-voracious freezers. In favorable cases, the recent advent of room temperature sample storage prevents the degradation of biological materials, enabling safe storage at room temperature.¹ Using RTSS approaches, biomolecules such as DNA, RNA, and bacteria can often be stabilized at ambient temperatures, providing a cost-effective alternative to cold storage. Another way is to set your ultra-low temperature freezers -60 to -70°C instead of -80°C.

As recently as a few decades ago, the standard sample storage temperature was -60°C. The shift to cooler settings happened only after manufacturers marketed the ability to reach lower temperatures.² Independent groups and labs have shown that an increase in temperature provides sample preservation that is effectively the same as when samples are stored at -80°C but results in up to 30 percent less energy use in older ULT freezer models and up to 22 percent less in newer, more energy-efficient models.^2–6 A warmer temperature setting, such as -70°C, also reduces wear and tear on the freezers, which reduces maintenance needs.

It was once challenging to find an energy-efficient lab freezer or refrigerator—not so anymore. ULT freezer manufacturers have made great strides in energy efficiency with the traditional dual-stage cascade refrigeration systems. Moreover, new compressor-free freezers that use the Stirling cycle for cryogenic cooling reported a 50 percent reduction in energy consumption compared to conventional ULT freezers of similar size.⁷

In this article, I’ve focused on dual-stage cascade refrigeration systems, which represent most ULT freezers used in academic research laboratories. For a general comparison of dual-stage cascade and Stirling engine ULT freezers, see the Newlife Scientific website⁸ or this YouTube video. Here, I compare key parameters for researchers to consider to make well-informed decisions on cascade refrigeration systems, such as temperature stability, energy efficiency, capacity, maintenance requirements, and cost-effectiveness.⁹

1. Temperature stability – Temperature stability is a critical factor in preserving the quality and viability of samples. Single-compressor freezers use a single cooling system, which can lead to temperature fluctuations under moderate to heavy use. In contrast, dual-compressor freezers house two compressors that work in a cascade, two-cycle system or use the second compressor as a backup, ensuring greater temperature stability.
   Both energy-efficient and standard upright ULT freezers can reach and maintain ultra-low temperatures, typically around -80°C or even lower. However, energy-efficient models often use advanced cooling technologies and improved insulation to enhance temperature uniformity and stability. These advancements help ensure precise temperature control and minimize temperature fluctuations that could affect sample integrity.
2. Energy efficiency – Energy consumption is a significant consideration to minimize operating costs and environmental impact. With technological advances, single- and dual-compressor UTL freezers can be reasonably energy efficient. Energy-efficient upright ULT freezers are designed to reduce energy consumption while maintaining extremely low temperatures. They can incorporate advanced insulation materials, high-efficiency compressors, optimized temperature control systems, or any combination of these features to help reduce electricity usage compared to standard models, resulting in lower energy costs and environmental impact. Manufacturers report their energy specifications as either kWh/day (kilowatt-hours per day) or kW/h (kilowatts per hour). When comparing different freezers, make sure you are using the same consumption units.
3. Capacity – The capacity of a freezer is crucial for accommodating different sample volumes. Both energy-efficient and standard upright ULT freezers are available in numerous sizes and configurations to accommodate different storage needs. They offer adjustable shelves, storage racks, and compartments to optimize storage space for samples of different sizes and quantities. It’s important to note that smaller ULT freezers are generally more energy-efficient. However, the actual energy consumption depends on factors such as the insulation quality, cooling system design, usage patterns, and the specific brands and models compared. When choosing a freezer, it’s a good idea to consider the energy efficiency ratings provided by the manufacturer and the available storage capacity and interior configurations when comparing specific models.
4. Maintenance requirements – Regular maintenance is essential to ensure optimal performance and longevity of freezers. Single-compressor freezers generally require less maintenance as they have a more straightforward design and fewer components. Dual-compressor freezers are more complex systems and may require more frequent servicing and potential downtime for maintenance activities. Specific maintenance tasks related to energy efficiency, temperature control, and alarm systems may be necessary for energy-efficient models. Regular temperature monitoring, routine cleaning, and adherence to manufacturer guidelines are essential for all types of freezers to maintain their performance, longevity, and sample integrity.
5. Cost-effectiveness Cost is an important factor for research laboratories, which often operate under limited budgets. Single-compressor freezers generally have lower upfront costs compared to dual compressor models. However, dual-compressor freezers can offer long-term cost savings due to their improved energy efficiency. On the other hand, it is also true that energy-efficient models often incorporate advanced components and technologies that may require specialized maintenance or replacement parts, affecting maintenance costs. When evaluating their cost-effectiveness, consider the potential maintenance costs associated with energy-efficient freezers.

ULT freezers house some of a research lab’s most precious and expensive reagents, so ensuring you have the right freezer to meet your needs isn’t just a luxury, it’s critical. The choice between single- and dual-compressor freezers or high energy efficiency and standard efficiency depends on the specific needs and priorities of the research laboratory. Single-compressor freezers may be suitable for labs with smaller storage requirements and limited budgets. In contrast, labs may want to consider dual-compressor freezers for larger storage capacities and higher demands for temperature stability.

Careful consideration of temperature stability, energy efficiency, storage capacity, maintenance requirements, and cost-effectiveness is crucial in selecting the most appropriate freezer type. While outside the scope of this article, do check out the new “Stirling freezers” that may represent a step forward even beyond the most sophisticated two-stage ULT freezer. Ultimately, the chosen freezer should meet the laboratory’s sample preservation needs while optimizing energy consumption and operating costs. And remember that -70°C works just as well as -80°C and will save energy, money, and wear and tear on your unit.

Acknowledgments: I sincerely thank Charles (Chuck) Sanders, Borden Lacy, and Benjamin Spiller for their invaluable guidance in composing this article. Their feedback was instrumental in gathering the necessary information for this piece and is greatly appreciated. There are no conflicts of interest to declare. This article does not represent an endorsement of a particular freezer brand.

Selene Colon is the Assistant Dean for Research Logistics and Compliance for the Vanderbilt University School of Medicine Basic Sciences

References:

1. Wan, E. et al. Green Technologies for Room Temperature Nucleic Acid Storage. Curr Issues Mol Biol 12, 135 (2010).
2. Plug load test for ULT Freezers: 20-22% lower energy consumption at-70 ^oC compared to-80 ^oC. http://groencampus.ku.dk/detgoervi/konkreteprojekter/groenindkoebsaftale/.
3. Beekhof, P. K., Gorshunska, M. & Jansen, E. H. J. M. Long term stability of paraoxonase-1 and high-density lipoprotein in human serum. Lipids Health Dis 11, 1–3 (2012).
4. Jansen, E. H. J. M. et al. Long-term stability of parameters of antioxidant status in human serum. Free Radic Res 47, 535–540 (2013).
5. Going Green: Tips for Achieving a Sustainable Lab | Labcompare. https://www.labcompare.com/360359-Going-Green-Tips-for-Achieving-a-Sustainable-Lab/?ctid=1&cid=139.
6. Delaney, P., California, S., Zeng, E. K., Livchak, D. & Ruan, E. PG&E’s Emerging Technologies Program Ultra-Low Temperature Freezers: Opening the Door to Energy Savings in Laboratories PG&E’s Emerging Technologies Program. (2016).
7. Berchowitz, D. M. & Kwon, Y. Environmental profiles of stirling-cooled and cascade-cooled ultra-low temperature freezers. Sustainability 4, 2838–2851 (2012).
8. Holden Galusha. Dual-Stage Cascade vs Stirling Engine ULT Freezers. https://newlifescientific.com/blogs/new-life-scientific-blog/dual-stage-cascade-vs-stirling-engine-ult-freezers (2021).
9. Questions to Ask When Buying an Ultra-low Temperature Freezer | Labcompare. https://www.labcompare.com/590178-Questions-to-Ask-When-Buying-an-Ultra-low-Temperature-Freezer/?ctid=1&cid=139.

Website Sources:

kW vs. kWh: What’s the Difference? | Direct Energy Regulated Services

Purchasing Energy-Efficient Laboratory-Grade Refrigerators and Freezers | Department of Energy

A Guide to Selecting an Ultra-Low Temperature Freezers – The Lab World Group

Energy Efficiency and Considerations for Upgrades – International Laboratory Freezer Challenge

ULT Freezer Comparison: Dual-Stage Cascade vs Stirling Engine (newlifescientific.com)