A Novel Building Module With Dual-Mode Radiative Thermal Regulation

With the increasing global energy consumption, researchers are striving to improve energy sustainability and utilization. The building industry accounts for 36% of global primary energy consumption, with HVAC systems consuming over 50% of the energy within the building sector. Passive radiative cooling (PRC) provides a promising solution for cooling without external energy input. However, current PRC systems lack self-regulation in response to external climate conditions, resulting in unnecessary cooling and additional heating energy penalties in cold days. A temperature-adaptive thermal management system with tunable output for both cooling and heating is urgently required.

Inspired by the self-folding leaves of the Mimosa pudica, we introduce a novel and dual-mode temperature-adaptive module (TAM) for architectural applications. The TAM features a bilayer Janus structure with materials of divergent thermal expansion characteristics, allowing autonomous switching between open and closed states in response to environmental climate variations. This innovative structure combines cellulose nanofibers (CNF) with negative thermal expansion coefficient and ethyl cellulose (EC) with positive thermal expansion coefficient. This strategic pairing of materials with opposing thermal behaviors enables the self-actuating mechanism that drives the module's temperature-responsive functionality without requiring external power or control systems. A waterproofing fluorinated silicon dioxide top layer enhances outdoor durability. The TAM is durable, UV-resistant, and colorizable, advancing thermal regulation technology for energy-efficient buildings adapting to climate variability.

The TAM demonstrates exceptional versatility through seamless integration with existing radiative cooling technologies. When combined with a PRC ceramic (solar reflectance: 99.6%), the system exhibits remarkable thermal regulation capabilities. Four color variants of the TAM—black, red, yellow, and blue—display distinctive solar absorption profiles of 95.6%, 90.6%, 74.5%, and 91.9%, respectively, while maintaining consistent functionality. Below the threshold response temperature, the TAM functions as a heat-absorbing and insulating layer, effectively retaining thermal energy. Conversely, when ambient temperatures exceed this threshold, the module autonomously retracts to expose the underlying cooler, thereby facilitating high solar reflectance and enhanced thermal emission.

Field tests confirmed the effective diurnal and seasonal/regional radiative thermal regulation of the TAM. It provides a thermal insulation effect, resulting in a temperature increase of 1.98 °C during cold nights and a decrease of 8.79 °C during hot days. Additionally, it offers up to 16.77 °C of additional heating in cold months/regions while maintaining cooling efficiency in warmer times. The module exhibits outdoor durability and comes in various colors to fulfill aesthetic and design prerequisites. This scalable and economically viable innovation represents a notable leap forward in building thermal management.