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The Problem:

About 2 million people around the world die each year of diseases preventable by widely used vaccines. In Africa and parts of Asia over half of all vaccines that require refrigeration spoil before they can be administered. Millions of lives and billions of dollars are lost due to a lack of refrigeration.

Solution:

For vaccines to be safely administered in rural parts of Africa and Asia one needs a novel inexpensive, easy to maintain refrigerator that provides World Health Organization and UNICEF compliant “chain-of-cold” storage of vaccines. It should run on free non-polluting solar energy and it should be built in-country.

Description:

The Appropriate Technology Collaborative (ATC) worked with engineering students and professors at Michigan State University to create a unique refrigeration technology.
The ATC Solar Vaccine Refrigerator is a robust, easy to maintain technology that can be made in the country or region where it is to be used. It is made out of simple materials that can be found in most cities: steel, charcoal and ethanol or methanol. The finished product has no moving parts that need maintenance and it doesn’t use electricity of any kind. One simply places it in sunlight and it freezes. Period. (Note: If the sun doesn’t shine it can run on biofuels)

Design:

Simplicity and sustainability guided the design of the Solar Vaccine Refrigerator. There are only a few parts connected together by pipe. A steel box filled with activated charcoal, a series of pipes with cooling fins and a container of ethanol. There are no valves in the system.

How it Works:

The steel box is the solar collector/adsorber. The box is painted black so that it converts sunlight to heat. When the solar collector gets hot in sunlight the charcoal rejects ethanol vapor. The rejected ethanol vapor flows into the condenser, which is a series of pipes with cooling fins. The temperature of the ethanol vapor is reduced to the ambient air temperature and it condenses into a liquid. The liquid then flows by gravity into the evaporator which is located inside an insulated box. At the end of the day we have liquid ethanol in the evaporator and cool charcoal in the adsorber. Cool charcoal can absorb ethanol vapor once again. At night some of the liquid ethanol is adsorbed back into the charcoal. The ethanol that remains behind in the evaporator becomes very cold and the temperature in the insulated box gets down to our pre-determined design temperature of 0 to -10 degrees Celsius.

Once each day the refrigerator goes through one cooling cycle. Thermal mass inside the insulated box keeps the internal temperature even throughout daily temperature swings.

Refinements:

We have also changed the geometry from the original prototype to use steel pipes filled with activated charcoal instead of the steel box. The round shape of pipe is structurally superior to a flat box so we can use thinner material and have fewer joints that need to be welded.