Session: 17-01-01: Research Posters

Paper Number: 150977

150977 - A Transparent Phase Change Hydrogel Window for Energy Efficient Building Thermal Regulation 

Energy-efficient thermal management for buildings is crucial for promoting sustainability and decarbonizing buildings, as heating, ventilation, and air conditioning (HVAC) systems account for approximately 30% of the total energy consumption in building sectors and one-third of the total global greenhouse house gas emissions. Among various methods reported for improving energy efficiency in buildings, thermal energy storage (TES) utilizing the latent heat of phase change materials (PCMs) has received emerging interest for reducing and shifting peak load without extra energy input. However, the practical implementation of PCMs is constrained by cost, shape stability, and energy density and focuses on opaque building envelopes (i.e., walls, roofing, and floors) applications. Limited research about PCM implementation in windows has been reported because the low light transmittance of PCMs during the crystallization decreases the visibility of windows, despite windows being one of the major sources of heat loss.

In this work, we fabricated a low-cost transparent phase change hydrogel (PCH) with exceptional shape stability and high energy density for energy-efficient window applications by incorporating sodium sulfate decahydrate (SSD) salt hydrates into poly (acrylamide-co-acrylic acid) hydrogel matrices. SSD offers an ultralow cost of $1.60/kWh, a high energy density of 180 J/g, and a suitable transition temperature close to the thermal comfort zone, while the hydrogel prevents the leakage of salt hydrates upon melting for excellent shape stability, owing to the absorption of hydrogel network to liquified salt hydrates. The hydrogel composition, synthetic condition (i.e., monomer ratio and neutralization degrees), and different SSD solution concentrations were optimized to improve the hydrogel encapsulation efficiency of SSD for high energy density. Our results demonstrated an optimized PCH composite with a high melting enthalpy of 133.3 J/g and a melting temperature of 32.8 ℃, while maintaining excellent shape stability without degradations in energy density and shifting in melting temperature after 500 hundred thermal cycles. For practical applications, a large-scale PCH with a diameter of 25 cm was fabricated. Our results demonstrated remarkable homogeneity, showcasing only a 2% variation in melting enthalpy among five different sampling sites. Additionally, benefiting from the intrinsic spectral selectivity of hydrogel composite, the PCH exhibited a 90% transmittance in the visible range at both melt and crystallized states while blocking 30% solar energy in near infrared range to suppress solar heating. Compared to a regular glass window, the proposed PCH window demonstrated a load shifting by 30 min in laboratory tests, revealing a cost-effective solution for implementing TES in window applications.

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
Zainab Faheem The University of Texas at Dallas
Shuang Cui The University of Texas at Dallas