SBIR-STTR Award

Air conditioning of building accounts for a major fraction of the U.S. primary energy consumption. Air conditioning is also a major contributor to electric utility peak loads, which incur high generation costs and generally use inefficient and polluting generation turbines. Peak loads are also a major factor in poor grid reliability. The proposed project focuses on shifting of thermal loads to lower the high utility peak loads, and also on enhancing the passive use of solar energy. Thermal load shifting will be realized through development of an innovative phase change material (nano-PCM), which is highly conductive for enhanced thermal storage and energy distribution, and is shape-stable for convenient incorporation into lightweight building components. This approach intimately associates the phase change material molecules with the large and compatibly functionalized surface area of exfoliated graphite nanoplatelets. Binding of the phase change molecules upon the nanoplatelet surfaces mitigates bulk liquefaction of nano-PCM upon phase change (providing for shape-stability). The percolated network of highly conductive graphite nanoplatelets provides nano-PCM with high thermal conductivity. Commercial Applications and Other

Benefits:
The technology enables effective, convenient and economical use of latent heat thermal energy storage in buildings for achieving the following advantages: (i) the ability to narrow the gap between the peak and off-peak loads of electricity demand; (ii) the ability to save operative fees by shifting the electrical consumption from peak periods to off-peak periods since the cost of electricity at night is 1/3-1/5 of that during the day; (iii) the ability to utilize solar energy continuously, storing solar energy during the day, and releasing it at night, particularly for space heating in winter by reducing diurnal temperature fluctuations thus improving the degree of thermal comfort; (iv) the ability to store the natural cooling by ventilation at night in summer and to release it to decrease the room temperature during the day, thus reducing the cooling load of air conditioning.

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.