In a typical American building, approximately 50% of the energy used is used for heating and cooling. Not only does this cost a lot of money and fossil fuels, it also puts a strain on already aging energy infrastructure, especially during periods of extreme temperatures. That's the question UC Santa Barbara researchers Charlie Shaw, Elliott Hawkes and Liao Bolin hope to solve.

In a paper published in the journal Device, they describe an adaptive tile that, when installed in an array on a roof, can reduce heating bills in the winter and cooling bills in the summer without the need for electronics.

"It can switch between a heating state and a cooling state based on the temperature of the tiles," said Xiao, the study's lead author. "The target temperature is about 65 degrees Fahrenheit -- about 18 degrees Celsius."

The roughly four-inch-square passive thermoregulator combines Liao's expertise in thermal science and Hawkes' work on mechanical design—a movable surface that changes its thermal properties in response to varying temperatures. The idea for the project came to them several years ago during a long trip between Santa Barbara and Northern California.

Tile development and functionality

"Our spouses were both at Stanford at the time, so we traveled together to see what we might be able to do together," said Liao, who, like Hawkes, is a professor of mechanical engineering at UC Berkeley. They subsequently received seed funding from the California NanoSystems Institute to design a mechanically tunable thermal device.

It wasn't until Shaw came up with the idea of ​​using wax motors that the idea of ​​adaptive tiles finally took shape. According to the change in the volume of the wax under the action of temperature, the wax motor generates pressure to move the mechanical parts and convert thermal energy into mechanical energy. Wax motors are commonly found in a variety of appliances such as dishwashers and washing machines, as well as in more specialized applications such as the aerospace industry.

In the case of tiles, the wax motor can push or retract the piston depending on its state, closing or opening the shutters on the tile surface. So, at cooler temperatures, when the wax is solid, the blinds close and tile, exposing a surface that absorbs sunlight and minimizes heat loss through radiation.

Advantages and test results

But once temperatures reach around 18 degrees Celsius, the wax begins to melt and expand, pushing the blinds open to reveal a surface that reflects sunlight and radiates heat. Additionally, during the melting or freezing process, wax absorbs or releases large amounts of heat, further stabilizing the temperature of the tiles and building.

"As a result, we have a predictable switching behavior that works within a very small range," Xiao explained. According to the researchers' paper, tests showed a 3.1-fold reduction in cooling energy consumption and a 2.6-fold reduction in heating energy consumption compared to non-switching devices covered with traditional reflective or absorptive coatings. Thanks to its wax motor, the device requires no electronics, batteries, or external power source to operate, and unlike other similar technologies, its response speed is within a few degrees of the target range. In addition, the device's simple design allows for easy customization - different thermal coatings and various types of wax can be used to allow the device to operate within the desired temperature range, while also facilitating large-scale manufacturing.

"This device is still a proof of concept, but we hope it will lead to new technology that can one day have a positive impact on a building's energy consumption," Hawkes said.

Compiled source: ScitechDaily