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< prev - next > Crop processing Crop storage and preservation KnO 100162_Refrigeration for developing countries (Printable PDF)
Refrigeration for developing countries
Practical Action
Nocturnal cooling in areas where clear night skies are common, can be effective. In air-
conditioning applications, the use of shade has been developed effectively in traditional
architecture, together with evaporative cooling by fountains and roof ponds.
Wherever possible passive methods should be used both in agriculture and architecture, since
they can be sustained locally and are economic. Only when cooling below 10°C is needed, is
it justifiable to look at active cooling technology, requiring complex machinery, and technical
maintenance programmes.
Sorption Heat driven coolers (HDCs)
The principle of sorption refrigeration is
Refrigeration phase: Because of low temperature in the bed
and low pressure, the refrigerant evaporates in the cold box,
drawing in heat, freezing water and cooling the storage space.
shown in Figure 3 which illustrates the
simplest type of sorption cooler and which
has an intermittent cycle consisting of two
phases. Continuous cycles are also possible
Refrigerant vapour releases heat while it recombines with the
sorbent which can either be a solid eg charcoal, calcium
chloride, or a liquid eg water.
Refrigerant vapour flow
- the Electrolux uses a continuous cycle.
The general term sorption covers both liquid
Nigh time
absorption and solid adsorption variants of
this technology. Sorption units have some
cooling phase
very important advantages. They can be
Cold box
designed to contain no moving parts, so
that skilled maintenance personnel and
Active cooling
replacements of components are less likely
to be needed. Secondly, they are simple to
store of ice
manufacture; local manufacture increases
local knowledge of the technology, which
improves operation, maintenance and
faultfinding. Thirdly, they are readily
Refrigerant vapour flow
Day time
cooling phase
adaptable to locally available fuels,
including biomass and solar energy. Finally,
Cold box
the refrigeration circuit does not use CFCs,
which damage the environment. Sorption
units are referred to as HDCs (heat-driven
No cooling
effect during
the day
Conventional gas and kerosene-driven
Cold stored as
sorption units
The heat source in conventional sorption
refrigerators is usually gas or kerosene
flame. Units powered from gas bottles are
used on caravans or boats. A domestic unit, Heat phase: At high bed temperature and systems pressure, the
often used in remote locations in
developing countries is the kerosene-driven
refrigerant is driven out of the sorbent and collects in the cold
box as a liquid.
Electrolux. It has been calculated that the
cost of purchasing and running one of these
units is around £1000 for 10 years use.
Figure 3: Sorption cooler.
Illustration: Neil Noble / Practical Action.
The refrigeration circuits of these devices
operate reliably for many years.
Maintenance of the burner assembly is required and a constant supply of wicks, burners and
lamp glasses are essential. Lastly, the fuel tank must be replenished with kerosene of suitable
quality. These units involve the use of hydrogen as a working fluid and cannot be designed as
efficient icemakers, although they have some ice-making capacity.
Novel sorption units
Novel sorption units are under development for greater efficiency in ice making and cold
storage. They do not involve hydrogen as a working fluid. A great deal of emphasis is being
placed on design for reliable operation in remote environments where technical maintenance
services are not available. Emphasis is also placed, in some cases, on design for local
manufacture. Costs and performance figures are not easily available since these units are still
on trial.