Understanding the energy implications of phase-change materials in concrete walls through finite-element analysis

Dwindling energy resources and associated environmental costs have resulted in a serious need to design and construct energy-efficient buildings. One of the strategies to develop energy efficient structural materials is the incorporation of phase-change materials (PCM) in the structural element. This paper presents details of a finite-element-based framework that is used to study the thermal performance of structural precast concrete wall elements with and without a layer of phase-change material. The simulation platform developed can be implemented for a wide variety of input parameters. In this study, two different locations in the continental United States, representing different ambient temperature conditions, two different types of concrete - normal weight and lightweight - two PCM types, and different PCM layer thicknesses are considered with an aim of understanding the energy flow across the wall member. The energy flow through the inside face of the wall, which determines the indoor HVAC energy consumption, is used as the defining parameter. Phase-change materials incorporating lightweight concrete wall design reduces HVAC costs in hot climates compared with the use of normal concrete. An ad hoc optimization scheme is also implemented where the PCM thickness is fixed but its location and properties are varied. Numerical results show (1) a slightly better response for PCM placed closer to the inside face of the wall compared with other locations, especially for hotter climates, and (2) energy savings are possible with small changes in baseline values, information that a PCM manufacturer can possibly use to design the next generation of phase-change materials.