This Small Business Innovation Research (SBIR) Phase I project proposes the development of a new type of cold thermal storage system that will help reduce the energy consumption of commercial and household refrigeration appliances. Central air-conditioning units and refrigerators account for nearly 30% of U.S. household electricity consumption. Cold thermal energy storage (CTES) technology has been proven to increase the energy efficiency of air conditioning and refrigeration appliances. However, much of the recent developments in CTES technology have been focused only on large-scale commercial air conditioning units. These developments have not been successfully translated to smaller scale industrial and household refrigeration appliances. The objective of this Phase I work is to overcome each of the major technical risks in the development of a small-scale cold thermal storage system by systematically studying, modeling and testing new types of thermal storage components and system configurations which will be incorporated into future energy-efficient refrigeration products.

The broader impact/commercial potential of this project is to reduce the energy consumption of power-hungry appliances such as refrigerators and air-conditioning units. Nearly 70% of all commercial buildings in United States use some form of refrigeration equipment, ranging from small refrigerators or vending machines to large refrigerated walk-in units. None of this equipment is designed to use energy efficiency technologies such as cold thermal energy storage. Cold thermal energy storage also has enormous market potential in developing economies where energy storage is not only an efficiency technology but is the ultimate key to enabling refrigeration in off-grid and remote locations where grid supply is unreliable or non-existent. In markets like India, farmers, food processors and public health institutions are clamoring for energy-efficient, grid-independent refrigeration appliances to store and preserve agricultural produce and vaccines.

Project Report

Promethean Power Systems develops energy storage systems for refrigeration applications. The systems can be used for cooling and storage of perishable products such as fruits, vegetables, milk and vaccines. Thermal energy is stored using phase-change materials encapsulated in a modular container, essentially a thermal battery that stores thermal energy rather than electrical energy. Multiple batteries can be connected together to meet any backup requirements. The resulting thermal battery pack can store and release large amounts of energy very quickly to cool perishable products immediately thereby preserving their freshness. Initial applications of these systems are in rural and farming areas of developing countries where electricity is only available for a few hours a day. The thermal battery pack stores energy whenever electricity is available and releases it when needed to cool the produce. This process eliminates the use of diesel generators, currently the only other backup option available in those areas. Refrigeration reduces spoilage, maintains quality and gives farmers a much needed boost in income. Another application for this technology is increasing the energy efficiency of refrigeration appliances. Nearly 70% of all commercial buildings in United States use some form of refrigeration equipment, ranging from refrigerators and air conditioning units to vending machines. Refrigeration equipment accounts for the majority of our electricity consumption and significant energy savings can be achieved by attaching a cold thermal battery pack to these appliances. The thermal battery will shift the electrical load from peak to off-peak hours when electricity is less expensive and temperatures are lower, thereby making the refrigeration appliances more energy efficient and cost effective. Research for this technology was funded in part by a National Science Foundation SBIR grant. Promethean is currently manufacturing and delivering commercial refrigeration systems to customers in India and plans to adapt the technology for use in dairy and brewing applications in United States. Further information and news can be found on-line at:

National Science Foundation (NSF)
Division of Industrial Innovation and Partnerships (IIP)
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Muralidharan S. Nair
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Promethean Power Systems
United States
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