The research could be a boon in hot countries where fridges and air-conditioning systems are vital, say the group of young scientists working at the Innovationszentrum Wiesenbusch Gladbeck (IWG), in cooperation with the University of Applied Science in nearby Gelsenkirchen.

"If you've ever had to go behind your refrigerator, you may have noticed that cold makes heat," said Rainer Braun, a professor at IWG. "That is, the apparatus which keeps your food cold is often too hot to touch. Why, then, can't heat make cold?"

"Anybody can produce heat by producing coolness," Braun said. "But we at IWG are the only ones producing coolness from heat."

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Hot countries may be particularly interested in the new cooling technology

It is a question of particular importance in hot countries, where food goes bad quickly and interiors need air-conditioning.

The problem is, though, that cooling is very energy-intensive, and can put stress on electrical generation systems. So why not look to the biggest source of energy available: the sun?

The principle of solar cooling, the so-called ammoniac-water absorption technique, has been known since 1810.

In Gladbeck, this idea has been extrapolated to the idea of using warmth from other processes such as the heat of baking ovens.

Cutting-edge facilities

The German scientists have developed a prototype which very soon could be cooling a cold storage plant in Morocco this way. Another pilot facility in Gladbeck uses the warmth of a gas turbine to air-condition a lecture hall.

Currently, the IWG is actively recruiting technology companies to rent space in their buildings in northwest Germany which include some six universities and schools of applied science as well as several international airports.

"At the risk of committing an awful pun, it's a cool place to do some hot research," Braun said.