The race to design individual cooling devices
According to the IEA « Baseline Scenario », energy needs for space cooling could triple by 2050 (see IIR website news (1)). The home cooling industry is a large market: for example, in the US – where three-quarters of all homes use an air conditioner– air conditioning costs Americans USD29 billion per year, according to the US Department of Energy (2) . Cooling individuals could be less energy-consuming and a lot cheaper than cooling entire buildings. Based on that principle, companies, startups, and researchers are racing to build wearable devices that can act like mini air-conditioning units (3) :
Japanese company Sony plans to start selling a device called the Reon Pocket in 2020, just in time for the Tokyo Olympics. Reon Pocket is a Peltier effect-based device which is placed against the back of one’s neck, from where it can either lower or increase the body’s temperature. After performing hundreds of simulations, Sony claims this device – which weighs 85 g – can lower the wearer’s body temperature by 13 °C or raise it by about 8 °C. The projected price of the device, which will only be on sale in Japan at first, is about 130 USD.
US Embr Labs startup has designed the Embr Wave, a low-energy wearable thermal device to improve whole-body thermal comfort. The device is worn on the wrist and has a 25mm×25mm contact heating and cooling surface. The maximum heating and cooling power of the wristbands is 2W. A 2018 study at UC Berkeley’s Center for the Built Environment (4) based on tests on 23 subjects in a climate chamber found that the local warming and cooling had a significant effect for subjects who felt cool or warm before using the device. The Wave Bracelet is sold at about 300 USD.
The Embr Wave and the Reon Pocket both use the thermoelectric effect to generate cooling in a device that’s small enough to wear on the body. But thermoelectrics also require a lot of energy. According to Fast Company (3) , to make the Embr Wave more efficient, the startup’s team engineered the thermoelectric device to just target the temperatures that the human body responds to the best. Because temperature sensations are relative, the device has to be a little cooler than the normal human body temperature. The device’s temperature rises and falls slowly, thanks to a proprietary algorithm that alters the temperature just enough to produce a cooling sensation while saving battery. Embr says that users can run the device’s two- to three-minute cycles up to 50 times on a single charge.
Meanwhile, academic researchers are also exploring the ways that the Peltier effect can be used to create wearables. At the University of California San Diego (US), mechanical engineering and materials science professor Renkun Chen and his team created a wearable patch that uses similar technology to provide instant cooling (5).
The flexible patch, the development of which was funded by the US Department of Energy, also uses the thermoelectric effect to cool but doesn’t require a heat sink because the patch has a layer of insulation between the side of the patch that lies against the wearer’s skin and the side of the patch that expels heat out into the environment. The ultimate goal is to combine multiple patches together to create smart clothing that can be worn for personalised cooling and heating. Chen’s team estimates that it would take 144 patches to create a cooling vest. This would represent a power of about 26W total to keep an individual cool on an average hot day.
“If wearing this device can make you feel comfortable within a wider temperature range, you won’t need to turn down the thermostat as much in the summer or crank up the heat as much in the winter,” Chen said. Keeping a building’s set temperature 12 degrees higher during the summer, for example, could cut cooling costs by about 70 percent, he noted.
He hopes to commercialise the technology – which is currently at the proof-of-concept stage – within a few years.
(1) IIR News 23930