Not All Sustainability Efforts Are Created Equal: What should be considered outside ENERGY STAR® when trying to conserve energy in your laboratory?

We are pleased to see the progress research organizations are making toward reducing climate impact while increasing energy efficiency, but with an energy crisis looming, it may be time to take a step back and look at the sustainability measures currently in place within your laboratory, and re-evaluate which tactics will have the greatest impact.  Did you know that besides data centers, laboratories consume more energy per floor space than any other type of facility? 

ULT freezers are at the top of the list next to fume hoods as the most energy-intensive piece of lab equipment. While many have now obtained ENERGY STAR® certification or a My Green Labs ACT label, there are alternative solutions that may offer even greater conservation effect within a given floorspace.

Just recently, the SU780XLE was tested in a competitive benchmark study by a third-party testing house named Green Light Laboratories, LLC.  This Medline Scientific article nicely highlights lessons-learned from the testing.

When looking at a freezer’s energy efficiency ratings, it appears most useful to consider a freezer’s Watts/Liter/Day (W/L/Day) consumption because it calculates a freezer’s energy usage according to its capacity, allowing end users to accurately compare across competitive units. Table 1 demonstrates the SU780XLE’s excellent efficiency measurements and shows the additional energy conserved if your freezer temperature is raised to -70°C.

Set Temperature

Energy Consumption



8.864 kWh/day



7.744 kWh/day



6.710 kWh/day


Table 1. SU780XLE Energy Efficiency data collected and published by Green Light Laboratories.

Green Light Laboratories also calculated that the Stirling Ultracold SU780XLE has an industry-leading 47% usable capacity per footprint percentage as shown below in Table 2.

Usable Capacity

745.20 Liters

Published Net Capacity

780 Liters

Unit Footprint

1587.3 Liters

Published Net vs. Usable Capacity

34.8 Liters Smaller

Usable Capacity as % of Footprint


Table 2. SU780XLE Usable Capacity Percentage

Standard, cascade, compressor-based ULT freezers are designed with a large base to house the compressors and engine components.  However, because these compressors are so large, they consume available storage volume.  If you select a freezer using the alternative free-piston Stirling engine technology, such as the Stirling Ultracold SU78XLE upright freezer, the space reserved for the engine is much smaller and sits on top of the sample storage.  Not only will it save you energy, if paired with a high-density racking system, you will maximize storage space and hold up to 700*, 2-inch sample boxes, requiring the least amount of energy per sample.   

In addition, selecting a freezer, like the SU780XLE, provides operational flexibility.  Buying a freezer with a dedicated setpoint temperature or finding a ULT-dedicated power outlet for your freezer is becoming a thing of the past.  The SU780XLE runs on 110 or 220V and has the energy conversion built into the system; standard plug, standard outlet, AND it will maintain ANY setpoint temperature along the -20°C to -86°C spectrum.

Compared with traditional compressor-based ULT freezers, the SU780XLE generates 70–75% less heat. This reduced heat output lowers the demand on the building’s HVAC systems and should offer laboratories additional energy savings.

In summary, retiring your older ULT freezers and replacing them with a model like the SU780XLE employing 100% EPA SNAP-compliant natural refrigerants, you will not only reduce your energy consumption costs and associated carbon footprint, but also:

  • Reduce HVAC load
  • Limit your lab’s energy draw, but maximize storage
  • Maximize storage in a smaller physical footprint
  • Gain temperature flexibility along the -20°C to -86°C range; one system to do it all
  • Apply for regional energy utility rebates of up to $2500, depending on freezer location

[1] Freezer Challenge,

[2] Medline Scientific, Stirling Ultracold SU780XLE ULT Freezer: Reviewed

*To keep the vacuum release port unobstructed on the SU780XLE, it is recommended that one box be removed from the High-Density Storage Rack. This will reduce storage capacity to 699 2-inch boxes in the high-density configuration.

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