A research team at MIT has announced that they have successfully developed a system of passive refrigeration that can cool food or other substances using zero electricity. The system is being lauded as an invaluable means of achieving refrigeration for the preservation of food and medicine in off-the-grid locations.
The potential early applications could include supporting remote scientific research teams, delivering aid to poor and indigent populations in difficult to reach locations, undersea exploration, and for use in space.
The system utilizes the natural emission of heat at the middle infrared range, which passes out of the container into the surrounding atmosphere. The unit sheds heat passively while being shielded from the rays of the sun by a strip of metal suspended over the top which acts as a kind of advanced parasol.
The passive cooling system was described in the journal Nature Communications. According to the theory behind the device, it could generate cooling as low as 36 degrees Fahrenheit or 20 degrees Celsius below the background temperature in relatively mild climates like that of Boston MA in the Fall.
Under optimal conditions, the research team was able to achieve cooling as low as 11 degrees Fahrenheit. For applications that call for even cooler temperatures, thermoelectric cooling or conventional refrigeration technology could be conjoined with the passive system.
Previous attempts at passive cooling have relied on complicated photonic systems that are exorbitantly expensive. The photonic devices work by reflecting all light across all wavelengths while emitting heat via the middle infrared range. Another weakness of these designs is that any blemish to the exterior – however superficial – would reduce the ability of the system to resist the heating effects of the sun. Worse yet, the extremely low spacing tolerances between components make the design impractical in any real-world environment.
The real innovation of the MIT team came with their discovery that light can be effectively blocked across a wide spectrum with a simple, curved, narrow strip of reflective metal positioned at just the right angle covering the path of the Sun across the sky. The device can be made from simple and inexpensive materials like plastic and aluminum.
Department head, Evelyn Wang said, “It’s deceptively simple. By having a separate shade and emitter to the atmosphere – two separate components that can be relatively low-cost – the system doesn’t need the special ability to emit and absorb selectively. We use angular selectivity to allow blocking the direct sun, as we continue to emit the heat-carrying wavelengths to the atmosphere.”
The researchers have applied for patents and look forward to building practical Commercial Refrigeration units soon.
