Session: 17-01-01: Research Posters

Paper Number: 149928

149928 - All-in-One Composite Integrating Optical and Thermal Regulation for All-Season Building Thermal Comfort 

Heating, ventilation, and air conditioning (HVAC) systems primarily contribute to approximately 30% of the total energy consumption in buildings. Novel material designs that improve the energy efficiency of building thermal management are crucial for decarbonizing the building sector and promoting the sustainability of power grid infrastructure. Recent research endeavors have demonstrated the effectiveness of several thermal regulation methods, such as photothermal heating, radiative cooling (RC), and thermal energy storage (TES), in reducing the energy consumption of HVAC systems when implemented as roofings and envelopes. However, one common constraint of these technologies is seasonal dependency, as their static thermal regulation mode is more effective in certain weather conditions than others, hindering the overall annual energy saving efficiency. In contrast, thermochromic materials offer both heating and cooling modes in response to different demands by modulating sunlight irradiance on buildings under external stimuli. This dynamic thermal regulation is advantageous in improving building energy efficiency in varying weather conditions but is subjected to solar intensity and considerably less effective in mitigating temperature fluctuations. In this work, we propose a multidisciplinary roofing design that integrates photothermal heating, RC and TES in one composite for all-season building thermal comfort. The all-in-one bilayer consists of a temperature responsive Poly(N-isopropylacrylamide) (PNIPAM) hydrogel as a sunlight modulator that undergoes a transparent-to-opaque transition below or above a lower critical solution temperature (LCST), and a graphite-doped polyethylene glycol (PEG) composite as phase change materials (PCMs) for TES. During a hot daytime (temperature above the LCST), the opaque PNIPAM top layer exhibits a high solar reflectance of 74.5% that decelerates PCM’s melting and extends the TES working hours for cooling.  In contrast, on a cold day, the PNIPAM top layer becomes transparent at low temperatures (below the LCST). Combined with the high overall solar absorbance of the underneath graphite-doped PCMs (86%), the bilayer composite can effectively absorb and store solar energy, reducing the heating load. In addition, the intrinsic strong thermal emittance of PNIPAM hydrogel enables RC to facilitate the PCM recharge by dissipating heat through an atmospheric transparency window during nighttime. As such, the efficiency of TES is improved, especially in hot climates where the TES recharge is limited as the ambient temperature may exceed the crystallization temperature of PCMs even during nighttime. Our experimental results confirmed that this all-in-one PNIPAM/PCM bilayer exhibited superior thermal regulation capability under a solar simulator compared to PCM and PNIPAM individually. Furthermore, the PNIPAM/PCM bilayer exhibited excellent cyclability with less than 3% deviation in spectral modulation and can store up to 112 kJ/kg with shape stability after 10 thermal cycles, highlighting its durability for long-term use. This multidisciplinary roofing design not only dynamically switches the heating/cooling modes in response to different demands but also stores energy for thermal comfort regulation, ensuring energy efficient building thermal management in all weather conditions.

Presenting Author: Lyu Zhou The University of Texas at Dallas

Presenting Author Biography: Lyu Zhou is a postdoctoral researcher in the Department of Mechanical Engineering at The University of Texas at Dallas. He received his PhD from The State University of New York at Buffalo. His research interests include innovative materials and processes for light and heat management, decarbonization, and advanced thermal energy storage.

Authors:

Lyu Zhou The University of Texas at Dallas
Leshi Feng The University of Texas at Dallas
Shuang Cui The University of Texas at Dallas