A fire is usually the last thing you would reach for when trying to keep something cold. But a new DIY refrigeration system built by Greenhill Forge flips that logic on its head, using heat, water, and road salt to cool without a conventional electric compressor.

The experimental setup, shown in a YouTube video, cooled the section to around 5°C (41°F) while the surroundings were about 16°C (61°F). That is a substantial temperature drop for a system powered mainly by a fire, although it is still a prototype rather than a proven replacement for a household refrigerator.

The project explores an old engineering idea with a potential modern use. Refrigeration that can operate in places where electricity is scarce or unreliable.

The system uses a technique called absorption refrigeration, a process that has been around for more than a century. Instead of relying on an electrically driven compressor to circulate refrigerant, it uses heat to drive a chemical process that enables cooling.

Greenhill Forge’s design has two main sections: a generator and an absorber. The generator contains a calcium chloride solution and distilled water. When a fire heats the mixture, water vapor separates from the solution and travels through a pipe to a condenser, where it cools and returns to liquid form.

The liquid water then passes through a small adjustable valve into an evaporator operating under a strong vacuum. At the system’s very low pressure, about six millibars, water can evaporate at temperatures far below its usual boiling point.

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