Multiphysics design optimization model for structural walls incorporating phase-change materials

Abstract

The development of energy-efficient building envelopes has been an ongoing effort in many countries owing to the pressing need to achieve energy independence. In this study numerical optimization techniques and finite element analysis provide the means to find a compromise point between adding phase-change materials (PCMs) to a concrete wall, the energy savings and the wall's structural capacity. The primary objective is to minimize the overall lifetime cost of a wall by understanding the implications of PCM layer thickness, material properties and position in the wall on the overall energy consumption. While it is difficult to manually configure a typical wall for the lowest total cost, the developed computational framework provides an automated tool for searching for the best design. The results show that successful designs can be obtained where material and energy costs can be minimized through a judicious combination of existing building materials with thermal energy storage materials.

Keywords:

• numerical optimization
• phase-change material
• finite element analysis
• cost minimization

Acknowledgements

The contents of this article reflect the views of the authors who are responsible for the facts and accuracy of the data presented herein, and do not necessarily reflect the views and policies of the funding agency, nor do the contents constitute a standard, specification or regulation.

Funding

The authors gratefully acknowledge the support from National Science Foundation [grant number CMMI 1130028] towards the conduct of this study.

Notes

1. This study considers the effects, in terms of both energy use and cost, of PCMs being added as separate strata (layers) in concrete. This is because more needs to be understood about the implications of direct addition of either bulk or microencapsulated PCMs in cementitious systems with respect to the development of concrete properties and the longevity of PCMs in such environments.

2. Microencapsulated PCMs are easy to incorporate in concrete elements even in situ, whereas bulk PCMs can be effectively introduced into the void space between the concrete layers only when they are in their liquid state, thereby requiring the local environment to be warmer than their phase-change temperature. While this could be easily accomplished in a precast concrete manufacturing facility, it poses some challenges in in situ construction.