Refrigeration for developing countries
Practical Action
Solar-powered sorption units
The heat source for sorption units of the kind shown in Figure 3 can be the sun. In a simple
version the heating phase ends at sunset, and the refrigeration phase occurs during the night.
If the sun fails to shine for a few days, the ice made on previous days acts as a store of cold,
keeping the cold box at a low temperature while it gradually melts. It is expected that a unit
producing 100 kg of ice per day can be produced for £4,000 (including the cost of highly
efficient solar thermal panels), giving an ice cost of £0.03 per kg.
A project that Practical Action is working on in collaboration with SCORE at the University of
Nottingham is a thermoacoustic device that uses thermal energy from a stove or solar energy
that generates acoustic waves that then produce electricity.
http://peswiki.com/index.php/Directory:Acoustic_Generator:SCORE:Stove_for_Cooking,_Refrig
eration_and_Electricity
More information is available from Paul Riley, Score Project Director, on +44 (0) 0115 951
5600, +44 (0)7973 426 379 paul.riley@nottingham.ac.uk or Internal Communications
Manager Tara de Cozar in the University’s Communications Office on +44 (0)115 8468545,
tara.decozar@nottingham.ac.uk
http://www.score.uk.com/
Mechanical Compression
Grid electricity
Where a reliable electricity supply exists, the most economic option is to install a standard
compressor driven unit. Conventional refrigerators of this kind are sold commercially. As an
example, a unit making about 100 kg of flaked ice, for fisheries use, each day in tropical
conditions will cost £7000, not including the cost of storage containers for the ice, or
delivery. The power consumption would be in the order of 4 kW continuously. There will be
extra costs in the form of replacement parts, maintenance and ancillary equipment.
Water turbine driven coolers
Costs can be reduced if shaft power is used directly to drive the compressor, for example from
a water turbine. An auxiliary electricity supply is useful to provide control and protection
functions, and for instance to drive ventilation fans. It is nevertheless feasible to design
wholly mechanical cold storage and ice-making systems.
Diesel generating sets
The cost of operating a generator in rural areas is dependent on local conditions and must be
assessed in the light of local experience. Quite often the cost can be very much higher than
expected because of the need for maintenance personnel and the difficulties encountered in
obtaining fuel and spare parts. If the generated electricity is not available continuously then
the refrigerator should be designed as an ice-maker, allowing cold to be stored in the form of
ice. Experience has shown that systems involving the storage of electricity in batteries have
very high costs and are unreliable.
Solar photovoltaic systems
Solar energy is an intermittent power source, usually available for 12 hours every day. The
intensity of insolation is very variable. It can be converted by photovoltaic cells into
electricity, which is then stored in batteries, so that a continuous smooth electrical supply
can be provided to power a mechanical compression refrigerator. Also see Solar Photovoltaic
Refrigeration of Vaccines Practical Action Technical Brief.
The advantage of using solar power is that it is a source that can be relied upon, never to fail
for more than a few days. This reliability is very important in some cases, such as vaccine
storage, where loss of temperature control can spoil the vaccines completely. The battery is
designed to continue to provide electricity at night and on days when no sunshine is
available. In this application, the high cost of photovoltaic cells, batteries and control
equipment is justified. The size of the photovoltaic array and the battery capacity must be
carefully calculated to provide an economic system.
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