Session: 03-02 Phase Change Thermal Storage

Paper Number: 106796

106796 - Phase Change Material for Thermal Energy Storage in Buildings Based on Sodium Sulfate Decahydrate and Disodium Hydrogen Phosphate Dodecahydrate 

The worldwide increasing energy demand and 2050 net zero carbon target urge the globe to solve the energy challenge. Buildings account for one-third of all energy use worldwide, and heating and cooling are responsible for almost half of the energy consumed in buildings. To address the energy challenges in buildings, thermal energy storage (TES) has received significant attention in recent years as TES might offer an environmentally benign solution to grid resilience and the energy challenge while offering energy savings. In buildings, TES can be integrated into HVAC components such as heat exchangers, heat pumps, or A/C units. In operation, TES material would store the energy in low-demand times, and the stored energy would be utilized in high-demand times, resulting in controlling the peak load and improving energy savings.

One of the essential elements in the TES deployment in buildings is to develop high-performance, inexpensive, and durable materials for optimal system performance. Among TES systems (latent heat, sensible heat, or thermochemical), latent heat storage such as phase change materials is specifically appealing due to their high energy storage capacity, cost-effectiveness, low- to no toxicity, to name a few. Sodium sulfate decahydrate (Na₂SO₄.10H₂O) is one of the commonly investigated phase change materials as it is inexpensive, abundant, and has a high thermal storage capacity. However, it is prone to incongruent melting (i.e., phase separation upon melting), which results in poor stability. Sodium phosphate dibasic dodecahydrate (Na₂HPO₄.12H₂O) has high energy storage capacity and is congruently melting; however, the degree of supercooling is high. In this study, we synthesized a novel phase change material consisting of sodium sulfate decahydrate and sodium phosphate dibasic dodecahydrate. In addition, sodium tetraborate decahydrate (aka borax, Na₂B₄O₇.10H₂O) and milled graphite have been added to improve the PCM performance by reducing supercooling and improving long-term stability. The thermal performance of the phase change materials was characterized using differential scanning calorimetry to initially find the optimum phase change material composition and temperature-history method for long-term stability (150 melting-freezing cycles). The results showed that the best performance material has a concentration of 32 w% Na₂SO₄.10H₂O, 52 w% Na₂HPO₄.12H₂O, 12 w% milled expanded graphite, and 4% borax with a melting temperature of 28°C and melting enthalpy of 167 J/g. Furthermore, the supercooling of the PCM was less than 3°C. The system showed negligible performance decrease after 150 cycles. In conclusion, the findings suggest that the novel energy storage material developed in this might be utilized in 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 Multifunctional Equipment Integration 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 PhD 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.