Session: 03-01 Low Temperature Thermal Storage

Paper Number: 130517

130517 - Thermal and Cyclic Properties of Nanocellulose-Based Thermochemical Energy Storage Materials for Buildings 

Abstract: 

Buildings are a critical contributor to carbon dioxide emissions while accounting for one-third of energy consumption worldwide. Therefore, decarbonization of buildings is a critical part of the global efforts to combat the climate challenge. To that end, Thermal Energy Storage (TES) is a promising technology because it enables the storage of heat energy, which can be utilized when energy is in demand. Among various TES technologies, thermochemical energy storage (TCES) is one of the most promising TES technologies due to its high energy storage density and long-duration storage ability with negligible to minimal heat loss. Salt-hydrate-based chemisorption is a promising class of TCES due to its high energy storage capacity and optimal temperature ranges for space heating. In this approach, hygroscopic salts are utilized as most are nonflammable, nontoxic, inexpensive, abundant, and have high energy storage capacity. However, despite the distinct advantages of hygroscopic salts, several issues hinder their effectiveness, such as particle agglomeration and instability, which adversely impact the cyclic stability and thermal performance.

Our research has previously addressed the stability issue by incorporating crystalline nanocellulose (CNC) as a stabilizing framework. While pure salt showed instability, CNC-incorporated salts showed improved stability due to the CNC assisting in the retention of the structural integrity as a result of binding to the submicron salt particles without compromising the energy storage capacity. In this study, we investigated the thermal and cyclic properties of the new composite materials that consist of strontium chloride (SrCl₂) or a blend of SrCl₂ and calcium chloride (CaCl₂) impregnated in the CNC framework. The first novel composite consists of 80 wt% mixture of SrCl₂ and CaCl₂, and 20 wt% CNC. The second composite consists of 80 wt% SrCl₂ and 20 wt% CNC. The enthalpy of dehydration of composite materials was measured after hydration at a given relative humidity and temperature at a fixed hydration time. The stability was determined by conducting 50 hydration-dehydration cycles. It was found that both composite materials exhibit a high gravimetric energy density (≥ 600 kJ/kg) and volumetric energy density (≥115 kWh·m^-3).  Additionally, these CNC-salt pairs show excellent thermal reliability, with a reliability of ≥90% after 50 cycles. In addition to the cyclic performance, the peak of the heat flow curve during the cycles (dehydration temperature) was studied as they reflected the application temperature. It was found that most of the dehydration happened at temperatures ≤~70^oC, showing great potential for building applications. In addition to the cyclic performance, the thermal conductivity of the composites was investigated, given the critical role of heat transport in determining the efficiency of the materials in system integration. For both composites, the thermal conductivity of the materials in powder form was notably low (~ 0.1 W·m^-1 ·K^-1), because the thermal conductivity measurements of powders can be influenced by particle size, porosity, packing density, and the presence of interparticle voids. However, when the materials are compacted in a pellet form, a noticeable improvement (from 0.1 to 0.4 W/m·K) in thermal conductivity was observed compared to the powder form.

In conclusion, the findings of this study suggest that the novel thermochemical energy storage material of hygroscopic salt impregnated with CNC has enhanced cyclic stability and high energy storage capacity. The results indicate that these novel composite materials are promising for building heating and cooling applications.

Presenting Author: Tugba Turnaoglu Oak Ridge National Laboratory

Presenting Author Biography: Dr. Tugba Turnaoglu is an R&D Associate Staff in the Thermal Energy Storage Group at Oak Ridge National Laboratory. She is an experienced researcher in the field of ionic liquids and their applications, phase equilibria of gases, and advanced material development and deployment in buildings. Her current research interests include thermal energy storage (phase change materials and thermochemical storage), low–global warming potential refrigerants (sensing technologies and phase equilibria), and gas separation (air dehumidification and direct gas capture) technologies, as well as their applications in buildings.

Dr. Turnaoglu was previously a postdoctoral researcher in the Multifunctional Equipment Integration Group. During her postdoctoral appointment, she worked on numerous projects, including membrane-based and ionic liquid–based dehumidification, phase change materials, leak and sensing technologies of flammable refrigerants, heat recovery dishwashers, refrigerant maldistribution in heat exchangers, direct air capture, and heat-driven sorption heat pump heaters.

She received her BS in chemical engineering from Ankara University in 2009 and MS in chemical engineering from the University of Oklahoma in 2013. Dr. Turnaoglu received her Ph.D. with honors in the Department of Chemical and Petroleum Engineering at the University of Kansas in 2019. She is currently a senior member of the American Society of Chemical Engineers, an associate member of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers, and a member of the American Society of Mechanical Engineers.

Authors:

Tugba Turnaoglu Oak Ridge National Laboratory
Daniel Blake Montana State Univesity
Dilpreet Bajwa Montana State University
Adam Gladen North Dakota State University