Small, affordable, ultra-low-temperature vapor-compression and thermoelectric hybrid freezer for clinical applications

The storage of COVID-19 vaccines at low temperatures leads to the rising demand of ultra-low-temperature (ULT; between -40 degrees C and -86 degrees C) freezers. Current commercial ULT freezers are usually of large capacity and high cost and thus can be prohibitive for personal use. Cheaper, smaller-size ULT freezers would effectively address the needs of most point-of-use cold storage. Current portable freezers are mainly powered by thermoelectric modules. However, they require five or six stages to cool from room temperature to -70 degrees C with their low cooling capacity. In this work, we develop a small-size, low-cost, two-stage thermoelectric freezer in combination with a conventional compressor-based household freezer to reach -70 degrees C. Our design combines the high coefficient of performance provided by a vapor compressor and the accurate temperature control of Peltier coolers. The demonstrated hybrid ULT freezer could facilitate the transportation and storage of clinical products around the world and make vaccines more accessible to people in remote areas.