Evaporative Cooling, Electric-Free Refrigerators Part 2

Static Cooling Chambers

The Indian Agricultural Research Institute has developed a cooling system that can be built in any part of the country using locally available materials.

The basic structure of the cooling chamber can be built from bricks and river sand, with a cover made from cane or other plant material and sacks or cloth. There must also be a nearby source of water. Construction is fairly simple. First the floor is built from a single layer of bricks, then a cavity wall is constructed of brick around the outer edge of the floor with a gap of about 75mm (3″) between the inner wall and outer wall. This cavity is then filled with sand. About 400 bricks are needed to build a chamber of the size shown in Figure 3 which has a capacity of about 100kg. A covering for the chamber is made with canes covered in sacking all mounted in a bamboo frame. The whole structure should be protected from the sun by making a roof to provide shade.

After construction the walls, floor, sand in the cavity and cover are thoroughly saturated with water. Once the chamber is completely wet, a twice-daily sprinkling of water is enough to maintain the moisture and temperature of the chamber. A simple automated drip watering system can also be added as shown in Figure 3. (click image to enlarge)

Naya Cellar Storage

Practical Action Nepal has been successful in transferring cooler technology, similar to the Indian Agricultural Research Institute design, especially to rural areas. It is called the Naya Cellar Storage and was originally designed by Dr. Gyan Shresthra from the Green Energy Mission and Mr. Joshi. It is comparatively easy to adapt the design to the users’ requirements and the construction is made from locally available materials. The results have been encouraging for rural food processors who had little or no income and have been unable to acquire costly refrigerators.

The following basic materials are required to construct the Naya Cellar Storage:

  • Bricks -1200-1500
  • Sand – 400-500 Kilograms (880 – 110 lb)
  • Polythene hose – 6 meters (26″)
  • Water tank/bucket – 100 litre capacity (22 gal)
  • Bamboo/wood – 1.82 meters (6″) two pieces and 2.15 meters (7′) two pieces
  • Straw – 2 bundles
  • Sacks

Construction Details

Choose a small piece of land about 1.52 meters square (5’x 5′) facing away from the sun or where the sun does not shine directly. The ground should slope a little so that ground water drains away and does not seep into the chamber.

The size of the cellar storage can be varied to suit the user. The greater the volume to be stored, the bigger the size of the chamber. Normally, a 1.22.x 0.92 meters (3’x 4′) rectangular mortarless stone or brick structure is built to a height of around 1.22 meters (3′). A layer of sand, about 25mm (1″) thick is, spread on the ground over the area where the chamber is to be built and a layer of bricks or stones is laid onto the sand.

A doubled walled chamber is created from the bricks. The gap between the outer and inner wall of the chamber is about 125mm (5″). The cavity between these two walls is filled with clean sand. It should be free from soil to ensure against contamination from organic impurities. A high-density polythene hose with pinholes made along its length is laid on the sand within the cavity. The hose is blocked at the end so that water released from a tank spreads through these holes and keeps the sand moist. A thatched roof supported by four bamboo poles is placed above the cool chamber.

To keep the chamber cool, the circulation of air around the chamber must be unhindered. The air around the chamber is cooled by the effect of the water evaporating from the porous bricks and sand thus prolonging the shelf-life of the food stored within it. Sacks and bamboo sticks are used to cover the chamber, which is kept moist by sprinkling water.

Operation

To prevent damage to the fruit and vegetables they should be carefully stored in bamboo or plastic mesh trays/baskets takes place. The trays/baskets have four legs so that their contents are raised off the floor of the chamber. The flow of water through the hose needs to be regulated in response to changes in the outside temperature to allow conditions within the chamber to remain constant.

In one of the villages where Practical Action Nepal has been installing “Satso” solar dryers, one young mother also had a Naya cool chamber and was successfully storing cabbage and ginger for up to 2 weeks longer than she had done without the chamber. She used locally available stones from rivers to construct the walls, and covered the chamber with a piece of sack mounted on a criss-cross of bamboo.

source: www.practicalaction.org

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