Less carbon, more cold New cooling approach uses PCMs to freeze and cool perishables

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A technology developed by Oak Ridge National Laboratory keeps food cooled with phase change materials (PCMs) while reducing CO2 emissions by 30%.

More than 100 million residential refrigerators in the United States use up to 2 kilowatts of electricity every day. These refrigerators contribute to energy consumption and CO2 emissions by using compressors that run on and off around the clock, pumping refrigerants through evaporator coils to maintain low temperatures in the fresh and frozen compartments.

ORNL's innovation uses advanced evaporators with PCMs installed in each compartment for cold energy storage. PCMs are useful for heating and cooling because they store and release energy when transitioning from solids to liquids or vice versa. Researchers applied porous metals, direct contact defrosting technology and a low greenhouse effect refrigerant to improve performance and minimize environmental impact.

“PCMs are integrated with evaporator coils to keep temperatures constant, eliminating the need for one operating cycle and allowing refrigerators to operate at nearly 100% at night, when energy consumption is lower,” said Zhiming Gao of ORNL. “This reduces electricity demand, saves costs and maintains efficiency.”

Learn more about this technology:

New efficient refrigerator with cold energy storage that enables demand flexibility

Residential refrigerators typically use 1.5 to 2.0 kWh of electricity per day, and more than 100 million refrigerators are used in American homes, resulting in significant primary energy consumption and carbon emissions. This technology is a new household refrigerator that uses advanced evaporators with phase change material (PCM) based long-term cold energy storage, PCM thermal conductivity enhancement using metal foam material, direct contact defrosting technology and low global warming potential (GWP) alternative refrigerant, providing a efficiency improvements of more than 20% and peak load shifting are possible.

Description

This technology is a new refrigerator proposed to replace 100 million current refrigerators in the US. It uses advanced evaporators with phase change material (PCM) based long-term cold energy storage, PCM thermal conductivity enhancement using metal foam material, direct contact defrost technology and an alternative refrigerant with a low global warming potential (GWP) to achieve a flexible load demand management and achieve transformational efficiency improvements of more than 20%. This will enable a 30% reduction in CO2 emissions and an almost 100% load shift from day to night operation. The PCM is biologically based and can be integrated with evaporator coils to maintain constant temperatures for fresh and frozen foods. It only requires one cycle on and one cycle off, unlike current technology that cycles on and off repeatedly throughout the day. Replacing all conventional refrigerators in homes and commercial buildings with the proposed new refrigerator would save up to 167 TBtu of primary energy consumption and reduce CO2 emissions by 7.2 million tons. This replacement would directly support a smooth transition to achieving ambitious goals of net-zero carbon emissions by 2050 while creating millions of clean energy jobs. In addition, the power of the new refrigerator makes it possible to shift approximately 0.7% to 1.0% of daytime electricity demand to nighttime operation across the country.

Advantages

• Sustainable, reduces CO2 emissions by 30%
• Efficiency improvement ensures a reduced energy requirement of more than 20%
• Nearly 100% load shifting from day to night operation, saving energy and costs
• Helps achieve the goal of net zero carbon emissions by 2050

Applications and industries

• Refrigeration, residential and commercial
• Transport refrigeration

RESEARCHERS: Zhiming Gao, Kashif Nawaz. Mingkan Zhang

Images and article courtesy of ORNLUS Department of Energy