Sustainable, Cost Effective Ultra Low Temperature Freezers Update

Neill Lane, Global Cooling

Ultra low freezers powered by linear free-piston Stirling engines have been on the market for more than three years. More than 600 Stirling engine cooled portable, under counter, and large upright ultra low temperature freezers have been placed at universities, hospitals, pharmaceutical, and biotech sites throughout the world. The Stirling cooling engine uses helium working gas and is hermetically sealed at manufacture. The engine's two moving components are supported on gas bearings. The system uses no compressor, requires no oil and eliminates all contact between moving parts. The cooling engine modulates continuously to match the heat load on the cabinet, unlike the operation of cascade freezers where temperature is controlled by compressors cycling on and off.

More than 3,000 engines of this configuration have been built and incorporated in laboratory instrumentation applications over the last 15 years. Reliability has been good with current failure rates less than 1%. The free-piston Stirling engine attributes of high efficiency, compact size, long life and continuous modulation offer different benefits to the end user depending upon whether the engine is used in a small portable freezer or in a large standard size unit.

A 25 liter (0.9 cu. ft.) freezer using the Stirling engines weighs less than 20.5 kg (45 lbs.). This low weight allows the unit to be easily transported from one location to another. The unit has a universal power supply and can be powered with 110 or 220 volts at 50 or 60Hz; or 12V DC. Maximum current draw is less than 5 amps. For clinical trial applications and other dispersed deployment applications this ease of shipment and placement is unique. Traditional cascade compressor ultra-low freezers are typically much heavier and are configured to use either 110 or 220 voltage power, not both. The smallest commonly available conventional freezers are around 85 liters (3 cu. ft.) capacity and weigh between 68 and 113 kg (150 and 250 lbs.). Three to five times as heavy as the Stirling cooled unit.

The large, 780 liter (27.5 cu. ft.), Stirling cooled freezers offer a dramatic reduction in energy use, exceeding 50% in some cases, compared with the cascade compressor freezers. The full size Stirling freezer use less than 10kWh/day while storing 60,000 2ml vials. This unmatched low energy use results in significantly less heat rejected to the HVAC system, less infrastructure and back-up power, and quieter operation. Units have been field trialed at customer sites and compared with traditional cascade compressor units. Energy savings exceed 50% in some cases, recovery is comparable to conventional units and warm up from -80°C to -40°C, in the event of a power outage, is 75% longer.

Biography:

Neill Lane is President and CEO of Stirling Ultracold, Division of Global Cooling, Inc., Athens, Ohio. Previously he was a co-founder and the 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 funding and assistance to early stage, innovative technology companies, and for 10 years as President and CEO of Sunpower Inc., Athens, Ohio. Sunpower developed and manufactured Stirling engines and coolers for solar thermal electric power, household micro combined heat and power, radioisotope space power and cryogenic refrigeration. He led the development of Sunpower's in-house manufacturing and established its worldwide licensing activities. Mr. Lane was born and grew up in Zimbabwe and graduated with a degree in mechanical engineering from the University of the Witwatersrand, South Africa. He started his career as a lecturer in thermodynamics and has worked in clean energy.

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