TechNet-21 - Forum

This forum provides a place for members to ask questions, share experiences, coordinate activities, and discuss recent developments in immunization.
  1. Moderator
  2. Cold chain equipment
  3. Friday, 01 May 2009

by Joanie Robertson, Technical Officer, PATH

In March 2009, six companies submitted designs to PATH in response to its Battery-Free Solar Refrigerator Challenge. Product designs that meet desired specifications will receive financial assistance to cover the cost of third-party testing required for consideration under the World Health Organization's Product Quality and Service (PQS) process.

The purpose of the Battery-Free Solar Refrigerator Challenge is to encourage the development of new products in the solar refrigeration category for use in developing-country immunization programs. Solar-powered refrigerators are an attractive alternative to gas- and kerosene-powered absorption devices: they are environmentally sound, provide an alternative to grid electricity where it is unreliable, and can be produced affordably. However, most existing solar refrigerator products are inadequately designed to meet the needs of developing-country immunization programs. The main issues relate to the lack of or inappropriate replacements for exhausted batteries, inappropriate system sizing, and poor installation work.

The Battery-Free Solar Refrigerator Challenge is designed to help address the first of those issues. By providing clear specifications to known solar refrigerator manufacturers and helping facilitate the PQS testing and submission process, Optimize hopes to reduce some of the market barriers and spur innovation and growth in this important refrigeration category.

Larry Schlussler Accepted Answer
Sun Frost has been developing a prototype for a Battery-Free refrigerator. Test results for the refrigerator compartment were excellent. With the standard WHO solar day the compressor for the freezer will be off for 19 hours, almost a day in ambient temperatures of 32 C and 43 C. WHO standards require the ice pack freezing compartment remain less then -5 C during this period. During this 19-hour period with the freezer at –5 C no ice will melt. Given economics and practical size constraints of the refrigerator-freezer we have come to the conclusion that this is not feasible. We have come to this conclusion utilizing several different approaches: 1. By monitoring ice packs in the heavily insulated portion of our freezer compartment. 2. By calculating the heat gain into a small heavily insulated container. These results show that for a spherical storage space in a 32 C environment (a sphere minimizes surface area per unit storage) the thickness of the insulation must be well over an order of magnitude larger than the diameter of the storage space. It would of course have to be thicker at ambient temperatures of 43 C. 3. The difficulty of keeping ice packs from melting in a insulated container can also be seen by looking at test results for small vaccine carriers. In our test unit at the end of the 19-hour solar night the ice packs will be partially melted. A benefit of partially melting is that the ice packs will not be able to freeze the vaccines. We hope that this test standard can be re-examined in the near future so we can finish construction of our production model. Larry Schlussler PhD
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