Zero-energy cool chamber

Spoilage of fresh fruits and vegetables is a serious problem in tropical countries. Cool storage can prolong the life of fresh produce, but refrigeration equipment is expensive to buy, expensive to run, and expensive to maintain. There is, however, a practical, low-cost alternative for on-farm fruit and vegetable storage which employs the cooling power of evaporation. Zero energy cool chambers stay 10- 15° C cooler than the outside temperature and maintain about 90 percent relative humidity. And they are easy to build out of locally available materials, such as brick, sand, bamboo, straw, and gunny bags.

Living and breathing

Fresh fruits and vegetables are alive. They breath and ripen even after harvest. Cool temperatures stew this process, allowing you to keep your fresh produce longer and avoid spoilage.

Construction

1 Select a raised site close to a source of water.

2 Make a floor with bricks.

Make a floor with bricks.

3 Erect a double wall 70 cm high, leaving a cavity 7.5 cm wide between the two walls.

Erect a double wall 70 cm high, leaving a cavity 7.5 cm wide between the two walls.

4 Drench the chamber with water.

Drench the chamber with water.

5 Soak fine, river-bed sand with water.

6 Fill the cavity between the double wall with this wet sand.

Fill the cavity between the double wall with this wet sand.

7 Make a cover frame of bamboo, sirki, straw, or dry grass.

Make a cover frame of bamboo

8 Build a thatched-roof shed over the chamber to shield the chamber from direct sun and rain.

Build a thatched-roof shed over the chamber to shield the chamber from direct sun and rain.

Operation

- Keep the sand, bricks, and top cover of the chamber wet.

- Water twice daily, in the morning and evening. A drip system can be built with plastic pipes, microtubes connected to an overhead water source.

- Store your fruits and vegetables in perforated plastic crates. Do not use bamboo, wood, or fibreboard boxes because these will be damaged by moisture.

Water twice daily.

Watering with drip system

Cover these crates with a thin polyethylene sheet.

Rebuild the chamber with new bricks after 3 years. (The bricks' pores become blocked over time and this reduces the chamber's effectiveness. )

Advantages

- Can be constructed by an unskilled person No mechanical or electrical energy is needed.
- Allows small farmers to store produce for a few days and thus avoid costly rush selling.
- Ideal for household storage.
- Reduces losses and thus pays for itself in a short time.
- Useful for temporary storage of curd, milk, and cooked food.
- Can also be used for mushroom cultivation, raising silk - worms, and storage of biofertilisers.

Disadvantages

- Requires a significant capital investment
- Operation relies on a reliable source of water throughout the year.

Shelf life of fruits and vegetables in zero- energy cool chamber

Notes

Build your chamber on a site where breezes blow.
Build on an elevated site to avoid waterlogging.
Use clean, unbroken bricks with good porosity.
Sand should be clean and free of organic matter, clay, etc.
Keep the bricks and sand saturated with water.
Prevent water drops from contacting stored produce.
Keep the chamber clean.
The empty chamber should be treated with an approved fungicide and insecticide.

Caution

Remove all produce before treating the chamber with insecticide or fungicide.

Cost of cool chamber

Contributor: Dr. S. K. Roy