UC Berkeley

Novel energy technologies have the potential to address climate change by efficiently using natural resources and reducing greenhouse gas emissions into our shared global atmosphere. In preparation for a future society powered by renewables, engineering solutions must include environmentally conscious and cost-effective methods to store, transport, and convert energy.

I have numerically investigated the use of latent thermal energy storage (TES) technology, with solid to liquid phase change material (PCM), to shift cooling loads to off-peak hours. I first non-dimensionalized differential equations describing sensible and latent heat transfer in the PCM, and their finite difference counterparts, in order to facilitate scaling for the wide array of asynchronous cooling applications that could benefit from this technology. Next, I compared closed form analytical solutions and experimental testing of a TES prototype with the numerical prediction of its melting and freezing processes. Both the analytical solutions and the experimental tests matched the predicted results within 10% agreement, validating the computational model’s capacity to capture the physics governing the transient behavior of the device with high precision and accuracy. As no adjustable parameters were tuned to maximize agreement, the numerical model can be effectively employed to determine the performance of different designs without the need to fabricate, charge, and test them.

Using this model, I explored potential improvements to power and refrigeration cycles for power plants and commercial buildings integrated with thermal storage. I accomplished this task by taking simple representations of these systems in MATLAB and transforming them into declared relationships between complex components using the dynamic programming language of Modelica. Simulations in integrated development environments of both languages demonstrate improvements of up to a 1.4% increase in power plant energy output and a 2.4% decrease in building chiller energy consumption with thermal storage. With thoughtful selection of the phase change material and better charging and discharging control strategies for the thermal energy storage, further performance enhancement of such systems can be achieved.