Session: K6-04: HEAT TRANSFER IN ENERGY SYSTEMS - ENERGY STORAGE II

Paper Number: 137355

137355 - Thermal Storage Cost Scaling Analysis to Determine Storage Material Figures of Merit 

Abstract: 

Space heating and cooling are two of the largest end uses of energy in the built environment. However, there is often a mismatch between the time at which their use is most needed and the time at whic they are most efficient and inexpensive. For example, cooling is needed during the hottest part of the day, but this is when air conditioners are least efficient and electricity is most expensive. This mismatch presents an opportunity for thermal storage to shift the thermal load on heating and cooling technologies to the times when they are most efficient. However, the cost and performance of thermal storage is largely dependent upon the materials they use. Much research has been conducted to lower the cost and increase the energy density of these storage materials. However, in our cost scaling analysis we find that it is often the contribution of heat exchangers that dominate the overall thermal storage system cost. When this is the case, the cost per unit storage is not the most important storage material property; instead, it is the thermal effusivity that most strongly affects the system cost. We have developed an analytical approximation for the depth of discharge that a thermal storage system can achieve when supplying a constant thermal power. This depth of discharge depends on the material properties, and from it we can find the optimal storage material geometry that minimizes system cost. We then develop a regime map that describes the storage material figures of merit for situations when the storage system cost is dominated by either the storage material, heat exchangers, or insulation. These figures of merit are the group of storage material properties that when increased will decrease the cost of a thermal storage system that lands in a particular regime. Finally, we show how cheaper heat exchangers could shift the paradigm, moving thermal storage systems out of the heat exchanger cost dominated regime.

Presenting Author: Jordan Kocher Georgia Tech

Presenting Author Biography: Jordan Kocher is a Ph.D. candidate in Mechanical Engineering at the Georgia Institute of Technology. He is part of the inaugural cohort of the Department of Energy's Building Technologies Office Innovation in Buildings (IBUILD) Graduate Research Fellowship. His research includes refrigeration and dehumidification cycles, desalination and atmospheric water harvesting, as well as thermal storage. His dissertation research involves the thermodynamics of lower critical solution temperature (LCST) mixtures and their use in a novel refrigeration and dehumidification cycle.

Authors:

Jordan Kocher Georgia Tech
Shannon Yee Georgia Tech