Low-Cost Evaporative Cool Storage Systems for Farm Produce

Every year, millions of tonnes of fresh fruits and vegetables are lost before they even reach consumers. Studies estimate that 30 to 35% of India’s total horticultural produce is wasted during harvesting, storage, and distribution. For small-scale farmers in rural areas-where electricity is unreliable or simply unavailable-conventional cold storage is out of the question. This is where the evaporative cool storage system steps in. It is a remarkably simple, low-cost storage solution that uses zero electricity to keep produce fresh for days longer than open-air storage. Let’s break down exactly how it works, how to build one, and why it matters.

What is an evaporative cool storage system? 🔗

An evaporative cool storage system, also widely known as a zero energy cool chamber (ZECC), is a small on-farm storage structure that lowers the internal temperature and raises the humidity-two conditions that slow down spoilage in fresh produce. It operates entirely on the principle of evaporative cooling, requiring only water and locally sourced materials to function. No fans, no compressors, no electricity bills.

The concept was originally developed in India by Susanta K. Roy and D.S. Khuridiya at the Indian Agricultural Research Institute (IARI), New Delhi, in the early 1980s. Their goal was straightforward: provide rural farmers with an affordable way to reduce post-harvest losses of perishable crops like tomatoes, leafy greens, and mangoes. Since then, variations of this design have been adopted across Africa, Southeast Asia, and Latin America.

The science behind evaporative cooling 🔗

Evaporative cooling is the same process that makes you feel cool when a breeze hits your damp skin. When water evaporates from a wet surface, it absorbs heat energy from the surrounding environment, causing the temperature to drop. At the same time, the moisture released into the air raises the relative humidity.

In the context of a cool chamber, water is held in a porous layer (usually wet sand between two brick walls). As dry, hot outside air comes in contact with this wet surface, the water molecules absorb heat and evaporate outward. This pulls heat away from the inner storage space, creating a cooler and more humid environment inside.

The effectiveness depends on ambient humidity. In hot, dry climates where relative humidity is below 40%, the evaporation rate is high-and the cooling effect is strongest. In humid, coastal, or monsoon-affected regions, the air is already saturated with moisture, so the rate of evaporation drops and the cooling benefit is reduced.

Structure and construction materials 🔗

One of the biggest advantages of the ZECC is that it can be built using materials available in virtually any rural area. Here is what you need:

Bricks form the double walls of the chamber. Porous, low-cost bricks work best because they allow moisture to seep through. River sand fills the gap between the two brick walls and acts as a water reservoir. Bamboo or wooden canes are used to build the frame for the chamber’s cover. Straw, dry grass, khaskhas (vetiver), or jute cloth is placed over the bamboo frame to create an insulating, moisture-retaining lid. Finally, water must be available nearby for regular wetting of the sand and cover.

According to the MIT D-Lab, brick cooling chambers can store approximately 400 kg of fruits and vegetables, though the actual capacity depends on the dimensions chosen during construction.

Step-by-step construction process 🔗

Building a ZECC does not require specialised skills. An unskilled person can construct one in a day or two. Here is a typical step-by-step process, based on guidelines published by Energypedia and IARI research bulletins:

1. Select the site 🔗

Choose a raised, shaded, well-ventilated location that is close to a water source. If natural shade is unavailable, you will need to build a simple thatched or plastic-sheet roof over the chamber.

2. Lay the brick foundation 🔗

Create a single-layer brick floor of approximately 165 cm × 115 cm. These dimensions are flexible and can be adjusted based on the volume of produce you want to store.

3. Build the double wall 🔗

Erect two parallel brick walls to a height of about 67.5 cm, leaving a cavity of roughly 7.5 cm between them. This cavity is the key structural feature of the chamber.

4. Fill with wet sand 🔗

Pack the cavity between the walls with wet river sand. The sand serves as the moisture reservoir-water seeps through it and evaporates from the outer wall surface, driving the cooling process.

5. Prepare the cover 🔗

Build a frame from bamboo or wood that matches the top dimensions of the chamber. Cover it with straw, dry grass, or jute sacking and secure it with rope or twine. This lid traps cool, humid air inside.

6. Saturate and activate 🔗

Thoroughly soak the sand and walls with water. Once fully saturated, sprinkle water on the sand and the cover two to three times a day to maintain the cooling effect.

7. Load the produce 🔗

Place fruits and vegetables inside the chamber in plastic crates or baskets-not directly on the floor. This allows cool, humid air to circulate around the produce freely.

Performance: how much cooling can you expect? 🔗

A well-maintained ZECC can reduce the internal temperature by 10 to 15°C compared to the outside ambient temperature and maintain relative humidity at around 90 to 95%. These conditions are highly favourable for short-term storage of most tropical fruits and vegetables.

Research conducted at IARI, New Delhi demonstrated that the shelf life of tropical fruits stored in a ZECC increased by 2 to 14 days compared to storage at room temperature-a 15-27% improvement. Weight loss due to transpiration was also significantly lower inside the chamber.

A study on a combined evaporative and solar adsorption cool chamber at Ehime University found that the shelf life of tomatoes was extended from 7 to 23 days when stored inside the system compared to open ambient conditions.

Temperature and humidity data from field trials 🔗

Field evaluations in Meghalaya, India showed that a ZECC maintained temperatures 10-12°C lower than external conditions while using roughly 850 litres of water over a 14-day period. Vegetables stored inside showed significantly less shrivelling and retained better overall appearance compared to those stored in the open.

Which produce works best in a ZECC? 🔗

The evaporative cool storage system is particularly suited for perishable, non-climacteric, and short-shelf-life crops that benefit from cool, high-humidity conditions. Common examples include tomatoes, leafy greens like spinach and amaranth, okra, brinjal (eggplant), capsicum, carrots, radishes, mangoes, and citrus fruits.

However, not all crops should be stored together. Certain fruits-like bananas and mangoes-release ethylene gas during ripening, which can accelerate deterioration of nearby ethylene-sensitive vegetables. Keeping ethylene producers separate from sensitive produce is an important storage practice.

It is also worth noting that the ZECC is designed for short-term storage-typically a few days to two weeks. It is not a replacement for cold chain infrastructure but rather a practical first step for on-farm storage before produce is transported to market.

Advantages of the zero energy cool chamber 🔗

Zero electricity requirement: The entire system runs on the natural evaporation of water. There are no energy costs, making it ideal for off-grid rural areas.

Low construction cost: A standard chamber can be built for as little as ₹5,000-10,000 (roughly $50-100), depending on local material prices. This one-time investment can pay for itself within a single harvest season by reducing losses.

Simple to build and maintain: No technical expertise is needed. The chamber requires only regular watering-twice daily in hot, dry conditions.

No chilling injury: Unlike mechanical refrigeration, the ZECC does not bring temperatures down to levels that cause chilling injury in tropical produce. The gradual, moderate cooling preserves cell structure and quality.

Multiple uses: Beyond fruits and vegetables, ZECCs have been used for temporary storage of curd, milk, cooked food, biofertilisers, and even for activities like mushroom cultivation and silkworm rearing.

Limitations to keep in mind 🔗

Climate dependence: The system works best in hot, dry conditions. In coastal or tropical humid regions, especially during the monsoon, cooling performance drops significantly because the air cannot absorb much more moisture.

Water requirement: Although modest compared to irrigation, the chamber does need a reliable water supply. In water-scarce areas, this can be a constraint.

Periodic rebuilding: Over time, the sand accumulates salts and debris, and the bricks lose their porosity. Experts recommend replacing the bricks and sand every three years for optimal performance.

Limited storage duration: The ZECC extends shelf life by days to a couple of weeks-not months. It bridges the gap between harvest and sale but does not replace long-term cold storage for commodities requiring prolonged preservation.

Global adoption and ongoing research 🔗

While the ZECC was born in India, it has since been trialled and adopted in numerous developing countries. MIT D-Lab has collaborated with partners in Uganda, Mali, Rwanda, Burkina Faso, and western India to evaluate, build, and disseminate brick evaporative cooling chambers. Their research has helped establish best practice guidelines that make the technology more accessible to farmers globally.

More recent innovations include forced-air evaporative cooling chambers built inside shipping containers, which provide more controlled pre-cooling for larger volumes of produce. The MIT spinout CoolVeg Foundation is working to commercialise such designs for hot, dry regions where small and medium-scale farmers need affordable cold chain entry points.

Researchers are also exploring hybrid designs. For instance, a team at Ehime University combined evaporative cooling with a solar-powered adsorption refrigerator that produced ice to further lower the storage temperature-all without grid electricity. These developments suggest that the basic ZECC concept has significant room for improvement and scaling.

Why it matters for food security 🔗

India alone loses food worth an estimated ₹1.53 trillion (approximately $18.5 billion) annually due to post-harvest waste, with fruits and vegetables accounting for the largest share of those losses. Globally, the FAO estimates that about one-third of all food produced for human consumption-around 1.4 billion tonnes-is lost or wasted each year.

For a smallholder farmer earning a modest income, even a few extra days of freshness can mean the difference between selling produce at a fair price and watching it rot. The ZECC gives farmers the ability to time their market visits, avoid distress selling, and negotiate better prices-all with a structure that costs less than a basic mobile phone.

In the broader picture, reducing post-harvest losses through technologies like the ZECC contributes directly to UN Sustainable Development Goal 12.3, which targets halving per capita food waste and reducing food losses along supply chains by 2030. When every kilogram saved is a kilogram that doesn’t need to be re-grown, the environmental benefits-saved water, soil, and energy-add up quickly.

What do you think? Could simple, zero-electricity technologies like the ZECC play a meaningful role in reducing food waste in your region? And what other low-cost innovations have you come across that help farmers store their produce better?

References

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC3602570/
2. https://energypedia.info/wiki/Evaporative_cooling_chamber
3. https://d-lab.mit.edu/research/evaporative-cooling-vegetable-preservation/brick-cooling-chambers
4. https://www.sciencedirect.com/science/article/abs/pii/S0960148114004364
5. https://www.engineeringforchange.org/solutions/product/evaporative-cooling-chambers/
6. https://en.wikipedia.org/wiki/Evaporative_cooling_chambers
7. https://icrier.org/pdf/Policy_Brief_20.pdf