A battery-powered, wearable personalized temperature control system could help save energy on air conditioning and heating.
A research team from the University of California San Diego has created a wearable, soft and stretchable patch that can cool or warm a user’s skin to a preferable temperature and keep it there as the temperature around the person changes. The patches are powered with a flexible and stretchable battery pack that can be embedded into clothing.
“This type of device can improve your personal thermal comfort whether you are commuting on a hot day or feeling too cold in your office,” Renkun Chen, a professor of mechanical and aerospace engineering at UC San Diego who led the study, said in a statement. “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.”
To make the patch, the researchers soldered small pillars of thermoelectric materials made of bismuth telluride alloys to thin copper electrode strips and sandwiched them between two elastomer sheets made from a mixture of Ecoflex. A rubber material and aluminum nitride powder, which has high thermal conductivity. The battery pack, which is embedded in a stretchable material, is made of an array of coin cells that are connected by spring-shaped copper wires.
The device uses an electric current to move heat from one sheet to the other, driving heat along with current to cause one side of the patch to heat up and the other to cool down.
“To do cooling, we have the current pump heat from the skin side to the layer facing outside,” Chen said. “To do heating, we just reverse the current so heat pumps in the other direction.”
Currently, the patch is 5 by 5 centimeters and uses up to 0.2 watts of power, meaning that it would take about 26 watts of power to keep an individual wearing the patch cool during a hot summer day.
“If there are just a handful of occupants in that room, you are essentially consuming thousands of watts per person for cooling,” Chen said. “A device like the patch could drastically cut down on cooling bills.”
To test their concept, the researchers embedded a prototype device into a mesh armband and used it in a temperature-controlled environment.
The patch was able to cool the user’s skin to the desired temperature of 89.6 degrees Fahrenheit in just two minutes and kept the subject’s skin constantly at that temperature as the ambient temperature varied between 71.6 and 96.8 degrees Fahrenheit.
According to the study, the heating and cooling of buildings alone currently accounts for more than 10 percent of the total energy consumed globally.
Chen explained that the wearable device could put a significant dent into summer cooling costs, cutting costs by approximately 70 percent by keeping buildings 12 degrees higher.
While other personal cooling and heating devices exist, they often employ a fan or need to be soaked or filled with a liquid like water, making them inconvenient to wear or carry around.
However, a wearable patch that is comfortable and convenient to wear could overcome these obstacles.
“You could place this on spots that tend to warm up or cool down faster than the rest of the body, such as the back, neck, feet or arms, in order to stay comfortable when it gets too hot or cold,” first author Sahngki Hong, a UC San Diego mechanical engineering alumnus who worked on the project as a PhD student in Chen’s lab, said in a statement.
The researchers plan to continue to test their prototype, with the goal of combining multiple patches for smart clothing that can allow for the ultimate personalization of temperature. They are currently attempting to build a heating and cooling vest.
The study was published in Science Advances.