Solar Refrigeration

MSU Solar Refrigerator Team Guatemala

MSU Solar Refrigerator Team Guatemala

The Michigan State University Design Team working on the solar refrigerator produced the following text:

Update:  The ATC/MSU Team won the Michigan State Edison Prize for their solar refrigerator design.  Check It Out Here!

Problem Statement

Many of the vaccines used to control diseases require cold temperatures for preservation. Without a reliable power infrastructure, developing countries often lack the resources for keeping these vaccines cool in the long-term, hampering the ability to adequately protect citizens. The Appropriate Technology Collaborative Student Design Team has been charged with the task of developing a refrigerator to solve this problem. The team has created the following problem statement:

Design an adsorption refrigerator capable of maintaining a temperature between 2°C and 8°C that utilizes passive solar energy and can be built in developing countries. The team’s final product will be a clear and comprehensive set of instructions for building the device.

The problem statement provides a broad but complete perspective of the project’s end goal. Beyond this description, the complexity of the design is defined by a number of requirements and restrictions.

Design Specifications and Constraints

The aim of the project is to build a low-maintenance and low-cost adsorption refrigeration unit that can be set up in areas that do not have an electrical infrastructure to support standard refrigeration systems. The primary goal of the refrigeration unit is to store vaccines in a temperature range of 2-8 C; however, the refrigeration will also be able to support low-level commercial use. Currently, vaccines are delivered in insulated boxes that are able to keep vaccines in the 2-8 C range for a short period of time. The refrigerator will be able to store, cool, and extend the life of approximately 4 liters of vaccines delivered to these target areas.

Target regions have been identified as areas where an electrical infrastructure is nonexistent, but sunlight is plentiful. Therefore, the refrigeration unit will rely mostly on solar power generated from the sun for its energy supply. An adsorption refrigeration cycle allows for a space to be cooled by using heat from the sun. The performance of this cycle depends heavily on the adsorbent and adsorbate pair chosen, total pressure of the system, and the temperature difference experienced by the solar collector during one cycle.

The adsorbent and adsorbate pair chosen for this refrigeration unit are activated carbon and ethanol because of their performance and availability. Activated carbon can be obtained by using coconut shells and ethanol can be found in locally-available alcoholic beverages. Ethanol is a corrosive substance that can cause untreated metal to corrode over time; therefore, the refrigeration unit will need to be made from materials which are resistant to corrosion. Activated carbon, in granulated form, can be very hard to handle and the design of the refrigeration unit will need to incorporate a subsystem that holds the carbon in one place. Since the adsorption refrigeration cycle depends on low pressure inside the system, the refrigeration unit will need to be leak proof. A low vacuum of about 29 inches Hg will need to be pulled on the system and that vacuum will need to be held for the duration of the unit’s life. Because the solar energy from the sun is used to add a certain amount of heat to the system, a solar collector will need to be designed such that it captures enough radiation and converts it into heat. The design of the solar collector will need to incorporate two additional factors. The adsorber needs to be heated during daytime to desorb the ethanol and needs to be cooled down during the night to adsorb the ethanol. However, activated carbon has poor heat conducting properties, and an uneven distribution of heat inside the activated carbon will reduce the amount of space the refrigeration unit is able to cool.

The design of the refrigeration unit will eventually be finalized to the point where manufacturing drawings and instructions are published on the Internet for anyone to build the refrigerator and use in the target areas. With this in mind, the design should integrate materials and processes that are domestically available in the target areas in order to reduce costs related with the build of the unit.

This task is a continuation of a two-semester project involving two design teams. The final prototype is planned to be built in Guatemala from March 7 to March 20.  The responsibility of this group is to finalize the design of the refrigeration unit for construction in the target areas before leaving for Guatemala.

Request Solar Refrigerator Drawings:  Solar Vaccine Refrigerator Drawings

Project Sponsor Background

The Appropriate Technology Collaborative (ATC), founded by John Barrie, is a non-profit organization with the goal “to design, develop, demonstrate, and distribute appropriate technological solutions for meeting the basic human needs of low income people in the developing world.” ATC works in collaboration with clients and other nonprofits (NGOs) to create technologies that are culturally sensitive, environmentally responsible, and locally repairable in order to improve the quality of life, enhance safety, and reduce adverse impacts on their environment. The ATC works hand in hand with the communities it is involved in and promotes a healthy relationship with the people within those communities to aid them in harnessing the ideas and technologies that have been created through the ATC. The ATC has produced many successful technologies in the past including bio fuels, energy systems, replacements for common kerosene lamps as a lighting source, and water purification. All of the designs that are created through the ATC are distributed freely online to anyone who wants to use or improve upon them.

The goal of this solar refrigeration project is to create a source of refrigeration that will aid the billions of people without access to electricity and refrigeration. This project has many possible positive applications from cooling beverages for sale in remote areas to producing ice for commercial/medical use, with the main goal targeting the refrigeration of temperature sensitive vaccines. With the guidance of John Barrie, other members of the ATC, and the previous work completed by Michigan State design teams we will design a feasible, proper solution.

The results and materials from previous teams on working on this project have been made available for the current team and will be used as needed.