Sustainable, Cost-Effective Ultra-Low-Temperature Freezers
Neill Lane, Stirling Ultracold, Division of Global Cooling, Inc.
Jason Thompson, Stirling Ultracold, Division of Global Cooling, Inc.
A new generation of ultra-low-temperature freezers powered by linear free-piston Stirling engines now reaching the market offer a dramatic reduction in energy use, exceeding 50 percent in some cases, compared with the cascade compressor systems used in existing ultra-low-temperature freezers on the market worldwide. A conventional full size (25 to 30 cubic feet) -80°C freezer uses about the same amount of energy as the average American household—more than 1 kW on average or more than 24 kWh in a day. High energy use results in significant heat rejected to the facility HVAC system, additional requirements for infrastructure and back-up power, and noisy operation. Depending on the electric power source, the freezer and HVAC system electricity use can cause production of up to 100 tons of carbon dioxide over the freezer life.
These new American-made freezers provide cooling at about twice the efficiency of a cascade system, thereby reducing electric power consumption, HVAC loading, electrical infrastructure and back-up power, and the noise generated by cooling fans. The Stirling cooling engine uses environmentally friendly helium as the working fluid and is hermetically sealed at manufacture. Two moving components are supported on gas bearings (similar to the operation of an "air hockey" table). The system uses no compressor, requires no oil, and eliminates all contact between moving parts.
Cooling is distributed to the interior of the cabinet through a sealed gravity-driven thermosiphon with no moving parts; a small amount of refrigerant (less than 20 percent of that used in a cascade system), evaporates at cabinet interior and condenses at the cooling engine. The thermosiphon operates isothermally so there is minimal temperature gradient in the evaporator and interior chamber walls.
The cooling engine modulates continuously to match the heat load on the cabinet, creating straight-line temperature performance, unlike the operation of cascade freezers where temperature is controlled by compressors cycling. Over the life of a conventional ultra-low-temperature freezer, the compressors are estimated to stop and start more than 180,000 times. In contrast, assuming no power outages, the free-piston Stirling engine may start only once in the life of the freezer.
The freezer cabinet employs vacuum insulated panels, and with the compact cooling system, offers the highest vial count per square foot of floor space for any freezer on the market. The freezer has a touch screen controller with a graphical user interface, a unique IP address, and an Ethernet connector so the user can observe the freezer performance from remote systems.
Biography:
Neill Lane is president and CEO of Stirling Ultracold, Division of Global Cooling, Inc. in Athens, Ohio. Mr. Lane was co-founder and president of Blight to Bright LLC, an Ohio developer of large-scale solar installations. He served as executive-in-residence with TechGROWTH Ohio, a pre-seed fund providing assistance to early stage technology companies, and as president and CEO of Sunpower Inc. in Athens, Ohio. Sunpower developed and manufactured Stirling engines and coolers for solar electric power, household micro combined heat and power, radioisotope space power, and cryogenic refrigeration. Mr. Lane led the development of Sunpower's manufacturing and worldwide licensing.
A native of Zimbabwe, Mr. Lane graduated with a degree in mechanical engineering from the University of the Witwatersrand, South Africa. He has worked in clean energy his entire career, from developing biofuels as a graduate student to leading the development of world's first solar thermal free-piston Stirling engine.