

Called the Wristify, the device is essentially a copper alloy heatsink that uses thermoelectric cooling to reduce the skin temperature of your wrist. Thermoelectric cooling is governed by the Peltier effect, which describes heating or cooling caused by electric current flowing across a junction of two different conductors. Basically, as current traverses these junctions, one side heats up while the other side cools down. If you have a series of these junctions, and put a heatsink on the hot side, you can create a very effective heat pump.

Peltier coolers aren’t efficient, but they do have the advantage of having no moving parts or circulating fluids. All you need is a Peltier heating/cooling element, a heatsink, and a battery. Throw in a wrist strap, and that’s exactly what the Wristify is.

Wristify diagram

Developed by four engineering students at MIT, Wristify makes you feel cooler by reducing the skin temperature of your wrist by just a few fractions of a degree per second, over a few seconds. The engineers are still working on finding the optimal cooling cycle, but so far they say that the best method is to cool your wrist by 0.4 degrees Celsius (0.7F) per second for five seconds, and then turn off for 10 seconds. With this pulse cooling, the students say that wearers perceive whole-body cooling of a few degrees Celsius. If needed, Wristify can also reverse its operation to provide heating instead.

The main advantage of a personal cooling solution is that it’s much more efficient than cooling an entire building. According to one of Wristify’s inventors, Sam Shames, heating and air conditioning account for 16.5% of USA’s total energy consumption. The team says that adjusting the temperature of a single building by 1C (1.8F) can consume 100 kilowatt-hours of electricity per month; Wristify, on the other hand (!), can be powered for eight hours by a small lithium battery. If everyone wore a Wristify, instead of relying on AC, some massive energy gains could be realized.

The blight of air conditioning units sticking out of windows

It’s also worth pointing out that the US is fairly unique in its love affair for AC in specific, and gross energy consumption in general. While 87% of US homes have AC, hotter countries such as Brazil and India only have AC in 11% and 2% of homes respectively. In India, where hot weather regularly causes huge, cascading blackouts, the power grid is so stressed that it couldn’t possibly accommodate more air conditioning. Wristify could significantly improve the quality of life for these people.

As an aside, I can’t help but wonder about the low-level physiological response when you wear Wristify. In hot weather, the human body’s natural cooling method is to pump more blood to your extremities and the capillaries under your skin — in effect, your body turns into a giant heatsink. If your wrist was always a few degrees cooler, I wonder if your circulatory system would permanently alter itself in some way.

Wristify is currently just a prototype, but the team hopes to bring it closer to market by using the $10,000 first prize that it won in MIT’s annual Making And Designing Materials Engineering Competition (MADMEC).


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