Origami-Inspired Radiant Cooling for Improved Thermal Health

The Problem

In its Annual Energy Outlook 2021, the U.S. Energy Information Administration (EIA) estimated that in 2020, electricity use for cooling the interior of buildings (space cooling) by the U.S. residential and commercial sectors amounted to about 10% of total U.S. electricity consumption. The electricity used for cooling in the residential sector amounted to about 16% of total electricity consumption and 6% of total U.S. electricity consumption; and in the commercial sector, which includes commercial and institutional buildings, about 12% of the total electricity and 4% of total U.S. electricity were consumed for cooling. Moreover, the IEA estimates that, without action to address energy efficiency, global energy demands for space cooling will more than triple by 2050.

Energy saving retrofits hold great potential for significant reductions in energy consumption. Radiant cooling devices that cool their environments by absorbing the infrared radiation emitted by all objects around them (radiation), and via direct contact with the surrounding air (convection) have potential to help save energy. Their main component often is a large radiator surface with integrated copper or polymer tubing that transfers heat to and from a closed water circuit through which chilled water flows, absorbing heat from the radiator. Importantly, the energy savings radiant cooling devices can provide depend on the temperature to which the water supply needs to be cooled. The larger the radiator surface, the closer to room temperature the water can be in order to achieve efficient cooling. This means that radiant cooling devices are limited by the size of their typically flat radiator surfaces.

Our Solution

Engineers and designers at the Wyss Institute and the Harvard Graduate School of Design have developed foldable polymer-based radiant cooling devices that are fabricated by lamination with integrated microfluidic water-circuits. Their design and fabrication uses origami-inspired printed circuit board and pop-up book fabrication techniques that enable the generation of complex 3D rigid structures from flat 2D assemblies, and translates the use of microfluidic principles developed at the micron scale for use in the chip sector to the scale of building interiors. The device’s flexible water circuit is made from a polymer film that can be further incorporated into OLED films for building lighting and entertainment applications, or for other functions such as acoustic performance.

By applying analytical models and physical investigation, the researchers showed that these new types of Origami-Inspired Radiant Cooling devices produce more surface convection because of their folded geometry and because they have surface areas that are about 50% larger than those of flat panels. As a result, their thermal performance is improved by up to 67%, which enables the use of lukewarm water instead of chilled water to efficiently cool a room. This also lowers the condensation risk, which exists when buildings operate simultaneously in cooling and heating modes. The team has also shown that bioinspired design and numerical optimization of the flexible water circuit can futher increase the device’s cooling efficiencies.