Recovery Act - Shape-Stable and Highly Conductive Nano-Phase Change Materials

Thermal energy storage systems balance out the discrepancies caused by the mismatch in the timing of energy supply and demand in alternative energy systems. In the case of solar space heating, for example, the intermittent supply of solar radiation requires storage of the excess daytime supply to meet the nighttime demand. Thermal energy storage benefits the energy-efficiency of buildings by controlling indoor temperature fluctuations, and by shifting the energy demand away from peak hours. The focus of the project is on development of a new thermal energy storage material which complements large latent heat capacity with desired shape-stability, thermal conductivity, heat and fire resistance, scalability, economy, sustainability, and versatility for use in diverse energy systems. The new hybrid nano-phase change materials (nano-PCMs) rely upon the molecular interactions of PCM with the enormous (functionalized) surface area of low-cost expanded graphite nanosheets as well as the support of PCM by a networked, thermally stable polymer to realize a highly desired balance of qualities favoring their broad transition to energy-efficient buildings and solar energy markets. Hybrid nano-PCMs are produced by simple intercalation of expanded graphite nanosheets, preserving the interconnected nature of nanosheets to render high levels of thermal conductivity. High thermal conductivity is key to timely mobilization of the whole volume of nano-PCMs towards latent heat storage in scaled-up building applications. The Phase I project developed simple processing techniques for production of hybrid nano-PCMs, and validated their ability to provide a distinct balance of latent heat capacity, thermal conductivity, and high-temperature stability of shape and mechanical performance. Building walls incorporating nano-PCMs were also developed, and their value towards control of indoor temperature fluctuations and shifting of thermal load in building applicaitons was demonstrated. Numerical analyses confirmed that nano-PCM building products can bring about major energy savings and thermal load shifts. The proposed Phase II project will build upon the Phase I accomplishments towards: (i) full development and thorough characterization of hybrid nano-PCMs and building products incorporating them; (ii) theoretical and experimental validation of the benefits of hybrid nano-PCMs in terms of energy-efficiency, thermal comfort and shifting of thermal load in different building systems and climatic conditions; and (iii) competitive market evaluation of the technology for identifying priority applications and viable routes to market transition. Commercial Applications and Other Benefits: Nano-PCMs offer a desired balance of performance and cost for convenient incorporation into building construction products. These products can bring about major gains in the energy-efficiency and life-cycle economy of buildings at viable initial cost. The significant energy consumption and greenhouse gas emission of buildings magnify the benefits of the technology. The near-term markets in energy-efficient building construction offer the potential to consume close to 10 million tons/yr of thermal storage materials. A 5% share of this market represents ~$200 million annual sales of nano-PCM. The diminishing resources of fossil fuels, and their environmental burdens and rising costs are key factors benefiting market acceptance of the technology.