Thermal Energy Storage for HVAC

Thermal energy storage (TES) is a promising solution to store and dispatch energy and shave peak electric load, reducing the operational cost of HVAC systems. During my postdoctoral research at NREL (2019-21), I worked on the design and development of TES technologies for integration with HVAC systems of buildings.

I helped in the design, fabrication, and experimental evaluation of the performance of a dual-circuit (capable to charge and discharge simultaneously) phase-change material (PCM) heat exchanger integrated with an air-conditioner. A PCM consisting of a porous graphite matrix soaked with n-tetradecane was used as the energy storage material. I developed a detailed transient heat transfer model of the TES module and validated it with standalone experiments. I also helped develop reduced-order modeling approaches to improve the computational efficiency of simulations and enable easier integration with building energy simulation platforms. Laboratory performance of the integrated system showed the potential of this technology to provide demand flexibility, including three potential benefits: 1.) Reduction in peak power and total energy required during the peak demand period, 2) potential cost savings to customers and load reduction for electric utilities, and 3) flexible operation to meet on-peak periods of different durations, or at a different time of day.

Publications

1. Huang, R., Mahvi, A., Odukomaiya, W., Goyal, A., Woods, J., 2022. Reduced-order modeling method for phase-change thermal energy storage heat exchangers, Energy Conversion and Management, DOI: https://doi.org/10.1016/j.enconman.2022.115692 (PDF)

2. Goyal, A., Kozubal, E., Woods, J., Nofal, M., Al-Hallaj, S., 2021. Design and performance evaluation of a dual-circuit thermal energy storage module for air conditioners, Applied Energy, DOI: https://doi.org/10.1016/j.apenergy.2021.116843 (PDF)

In another project, I helped in demonstrating the connection between energy and power density of TES modules by developing thermal rate capability and Ragone plots. They are commonly used to show the trade-off between energy and power in batteries. We showed that the performance of phase-change thermal storage not only depends on the storage material properties but is also a strong function of module geometry and operating conditions. This research can potentially help researchers and engineers to increase clean energy use with storage by developing optimized energy storage solutions.

Publication: Woods, J., Mahvi, A., Goyal, A., Kozubal, E., Odukomaiya, A., Jackson, R., 2021. Rate capability and Ragone plots for phase change thermal energy storage, Nature Energy, DOI: https://doi.org/10.1038/s41560-021-00778-w (PDF)