Researchers at Zeo-Tech GmbH in Unterschleissheim, Germany, have developed freezer boxes and mini refrigerators for mobile and stationary use that are designed to operate more efficiently in their respective application areas than current technology allows. As it is powered by heat, the adsorption-based cooling process can utilise a range of different energy sources. Mobile freezer boxes are already being tested in practice. Once they are charged via a normal power socket, they can be stored loss-free until used, when the cooling process is started at the touch of a button. After a short cooling time they reach deep freeze temperatures which are maintained over 24 hours.

Active cooling means that contents are kept cold longer than in conventional boxes that use ice packs or phase change materials (PCMs). Compared to Peltier devices which enable continuous cooling, the advantage is greater energy efficiency and the fact that a power source is not required during the cooling phase. What’s more, Peltier elements only allow a small reduction in temperature. Especially in summer this is frequently insufficient for many applications.

Based on the results from these portable boxes, the researchers extended the concept to continuous operation for stationary mini refrigerators. In their view, the main advantages are when silent operation is required or where heat is the only available power source. The absorption refrigerators that are currently used in the overwhelming majority of such cases have low energy efficiency and operate with ammonia and dichromate, both of which are harmful to health. In contrast, the new devices developed in the research project –which is supported by the German Federal Ministry of Economics and Technology – use environment- friendly and naturally occurring substances: zeolite and water. Compared to ammonia systems they are also at least 35% more energy efficient.