Easy available solution
• In India quality deterioration of horticultural produce takes place immediately after harvest due to lack of on-farm storage
• Maintenance of low temperature is a great problem In a tropical country.
• Refrigeration is energy intensive, expensive, not so easy to install and run in remote areas and not always environment friendly.
• Due to lack of cold/cool storage space a substantial amount of fruits and vegetables are lost after production.
• Considering acute energy crisis and lack of cool storage facility efforts made to develop low cost/low energy cool chambers.
EVAPORATIVE COOLING
• A gift of nature - principle depends on cooling by evaporation.
• As water evaporates it has a considerable cooling effect and faster the rate of evaporation greater the cooling.
• Evaporative cooling occurs when air, which is not already saturated with water, passes over a wet surface.
• Water evaporates into air raising its humidity and same time cooling the bed.
• Efficiency of evaporative cooler depends on humidity of the surrounding air.
• Very dry, low humidity air can absorb a lot of moisture so considerable cooling occurs.
• In extreme case of air that is saturated no evaporation can take place and no cooling occurs.
• In theory lowest temperature that can be reached is wet bulb temperature.
CONCEPT OF ZERO ENERGY COOL CHAMBERS (ZECC)
• Based on the principle of direct evaporative cooling zero energy cool chambers have been developed.
• The main advantages of this on-farm low cost cooling technology are:
1. It does not require any electricity or power to operate
2. Materials required like bricks, sand, bamboo etc. available easily and cheaply.
• It is a double brick-wall structure, the cavity is filled with sand and walls of the chamber are soaked in water.
• Even unskilled labor can build the chamber, as it does not require any specialized skill.
• Cool chambers can reduce temperature by 10-15 oC and maintain high humidity of about 95% that can increase shelf life and retain quality of horticultural produce.
• Small and marginal farmers can store a few days' harvest to avoid middlemen.
• Technology Vision 2020 has identified it as a low cost storage technology for 2020.
• National Horticulture Board is giving 100% grant in aid for the benefit of the farmer.
Construction
• Select an-upland having a nearby source of water supply.
• Make floor with brick 165 cm x 115 cm.
• Erect the double wall to a height of 67.5 cm leaving a cavity of 7.5 cm.
• Drench the chamber with water. Soak the fine river bed sand with water.
• Fill the 7.5 cm cavity between the double walls with this wet sand.
• Make top cover with bamboo (165 cm x115 cm) frame and 'sirki' straw or dry grass.
• A thatch/tin shed made over chamber to protect from direct sun or rain or snow.
• Keep the sand, bricks and top cover of the chamber wet with water.
• Water twice daily (morning and evening) to achieve desired temperature and relative humidity.
• Alternatively fix a drip system for watering with plastic pipes and micro tubes connected to an overhead water source.
• Store the fruits and vegetables in perforated plastic crates.
• Cover crates with thin polyethylene sheet.
• Cool chamber should be reinstalled once in 3 years with new bricks
• Utilize the old bricks for other purposes.
Low cost environment friendly commercial size cool chamber
• A low cost environment friendly commercial size cool chamber (6-8 ton capacity) has been developed utilizing the same principle of evaporative cooling.
• It is also a double brick-wall structure; the cavity is filled with sand and walls of the chamber are soaked in water from an overhead tank.
• The floor is made of wooden planks and the bottom of the chamber is provided with air ducts.
• Air is drawn with the help of an exhaust fan - can run for a specific time with timer.
• Like ZECC this chamber can also reduce temperature and maintain high humidity.
• Commercial cool chamber has been found to be useful for storage of citrus, banana, potato, tomato etc. and onion during the rainy season by stopping water supply.
• In apple growing areas of Jammu and Kashmir, Himachal Pradesh and Uttrakhand these chambers would be useful for storing apples after harvest until they are required for sale.
• This chamber can also be used as a pre-cooling chamber, for mushroom growing storage of bio-fertilizers.
Increasing the efficiency of commercial size cool chamber
Temperature and Relative Humidity
• Cool chambers were found to have maintained considerably and relatively low temperature compared to field, shed and room temperature respectively.
• Fluctuations in maximum and minimum temperature was found to be maximum under field conditions,
moderate in shed and minimum in CC (Table.1)
• The cool chamber maintained about 85-90% R.H. whereas both in shed and field it varied widely
• It has been found that the shelf life of fruits and vegetables held in cool chamber increased as compared to storage at room temperature.
• The physiological loss in weight (PLW) was also found to be lower in cool chamber stored fruits (Table.3).
• Efforts are being made to bring down the temperature to around 15oC during summer months so that it can be used conveniently for storage of tropical fruits without causing any chilling injury.
Crop Cool chamber Room temperature
SCOPE OF COOL CHAMBER
• Proposed cool chamber can be installed in different places of handling of fresh produce.
• In present practice fruits and vegetables arrive in the wholesale market early in the morning and are purchased by the retailer/consumer before noon.
• At present fruits and vegetables are handled in open shed the freshness is prone to considerable deterioration.
• It is suggested that a battery of such commercial size cool chambers can be installed in wholesale markets, which are located near the big metropolitan cities.
• Units can be installed in two rows with a corridor in between. Each unit will have two doors, one opening into the corridor and the other into loading/unloading platform.
• The ducts are open on the roadside as well as on the corridor. An overhead tank can perform the soaking of sidewalls and tanks.
• The trucks can perform the loading and unloading on the platforms of each shed.
• Fruits and vegetables stored temporarily in the cool chamber units before the transaction can retain freshness and quality.
CONCLUSION
• Proposed cool chambers can work on zero to very little energy and can retain the freshness of the fruit and vegetables for a short period.
• These units can be installed profitably where the fruits and vegetables are held temporarily viz.
• Farmer’s field, packing stations,
• Can work as pre-cooling unit
• Railway stations,
• Village mandis,
• Wholesale markets of metropolitan cities,
• Super markets,
• Retail markets,
• Big hotels,
• Institutional feeding places,
• Defense establishments in remote places
• Processing factories etc.
• If properly propagated and actually adopted availability of nutritious fruits and vegetables will increase and the consumer will pay less.
• The grower will also not be forced to make distress sale and will get better return.
