Passive Refrigerator

The Passive Refrigerator project began in the fall of 2012 and construction was completed in the spring of 2013.  As a two-person team, our goal was to make a commercial-scale walk-in refrigerator that uses less than 10 Watts of power, built for under $1000 in material.  The refrigerator is a super-insulated room in the basement of the Medway Community Farm’s farm-house, with a footprint of about 8 feet by 12 feet.

The refrigerator functions by freezing a large mass of ice during the ambient winter air and using that ice to keep the fridge-chamber cool for the rest of the year.  The ice is contained in about 1000 2-liter soda bottles, stacked up like firewood in a separate chamber behind the South wall.  During the winter, a small fan blows cold air from outside past the bottles, freezing them. During the rest of the year, a temperature-controlled fan will blow cool air from the ice chamber into the fridge chamber, whenever the fridge gets too warm.

The Medway community farm uses the fridge to store vegetables.  The system is designed to stay between 34°F and 41°F and maintain a fairly high level of humidity.

OutputHalf

These graphs were generated by my Matlab model describing the heat flux though the walls of the refrigerator during the warm half of the year. The lower graph shows how many 2-liter bottles of ice would melt in order to absorb the heat up to that point.

Please visit the Passive Refrigerator Project Blog for the information on this project.

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The finished design requires 1600 two-liter bottles. It takes longer than I expected to clean, fill, and seal them.

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The particle board interior wall of the refrigerator sits about 10 inches from the basement wall and is caulked to minimize air infiltration. The walls also have a plastic vapor barrier to prevent moisture buildup and further decrease infiltration.

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The gap between the particle board and the wall is filled with shredded waste styrofoam, a free, abundant, high-performance insulation. It can make a mess though.

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This is the floor layout for the refrigerator. The bottles will be housed in a separate chamber from the refrigerated area to keep the refrigerator from freezing.

 

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