Session: 17-01-01: Research Posters

Paper Number: 150708

150708 - Moisture Actuated Tunable Phase Change Materials for All-Season Building Thermal Comfort Control 

The escalating extreme climate conditions in the foreseeing future necessitate innovative solutions that provide energy-efficient building thermal regulation with a low carbon footprint, as the building sector accounts for 30-50% of the energy consumption in the United States and 30% of global carbon emissions. Thermal energy storage (TES) utilizing the latent heat stored in phase change materials (PCMs) during phase transition is one of the promising technologies to improve building energy efficiency by shifting and reducing peak loads. A critical challenge in PCM-based TES applications is the limited tunability of the operating temperature, especially for near-ambient applications, as most PCMs have a fixed transition temperature as designed. For instance, within buildings, the required operating temperature can significantly fluctuate between summer and winter, and even exhibit notable diurnal variations. This results in suboptimal PCM utilization, often leading to incomplete melting or no phase transition at all. Although a cascaded system utilizing multiple PCMs with different phase transition temperatures has been proposed to meet the varying use temperature requirement, the energy density of TES for each use case is reduced. Additionally, most PCMs store the energy through a solid-to-liquid phase change transition. Handling the liquid phase of PCMs during phase transitions (melting) has hindered practical TES implementation, especially in building envelopes. 

To address these challenges, this work reports a solid-state, shape-stabilized PCM with tunable phase transition temperatures for TES applications requiring various use temperatures. The tunability of phase transition temperatures of PCMs is achieved through moisture absorption/desorption into/from hygroscopic and semicrystalline PCMs. More moisture absorption into the PCMs reduces the crystallinity of the PCMs, leading to a lower phase transition temperature. Our experimental results demonstrate TES with an impressive phase transition temperature tunability of up to 7.2 °C (from ~18 °C to 35 °C). Meanwhile, outstanding shape stability over 120 hours without leakage during melting is also achieved by converting the traditional solid-to-liquid phase transition to a sold-to-gel transition through a sol-gel synthesis. Furthermore, the tunable TES exhibits exceptional cyclability, maintaining TES storage capacity of more than 500 cycles, without degradation in energy density and storage temperature, thus presenting a promising avenue for practical all-season building thermal comfort control applications. Our developed tunable TES will lead to adaptable energy storage for variable use cases and wide-ranging needs from end users, as well as benefit the grid flexibility requiring dynamic demand, which are keys to unlocking high-efficiency TES systems for decarbonization

Presenting Author: Shuang Cui The University of Texas at Dallas

Presenting Author Biography: -

Authors:

Roma Avhad The University of Texas at Dallas
Lyu Zhou The University of Texas at Dallas
Shuang Cui The University of Texas at Dallas