Evaporative Cool Chamber & A Cool Store With No Power
Stores vegetables
Enter your produce load and crate size to get the chamber footprint, the crates and capacity, the water per day and the bricks for a zero-energy cool store.
Size your cool chamber
Next: build a ~5.28 m² double-wall chamber for 25 crates, keep the sand cavity and top cover wet (83 L/day in hot weather).
Cooling depends on dry, breezy weather (more evaporation); not as cold as refrigeration but cheap and power-free — best for short-term holding of leafy/soft produce.
Cool chamber — key facts
- Crates
- produce ÷ crate weight
- Footprint
- set by the crate stack
- Temp drop
- 10–15 °C below outside
- Humidity
- ≈ 90%
- Build
- double brick wall, wet sand
- Power
- none — fully passive
- Best for
- short-term leafy/soft produce
- Privacy
- Runs in your browser; nothing uploaded
Keep produce fresh with bricks, sand and water
Not every farm has power for a cold room, but every farm can build a zero-energy evaporative cool chamber. Two brick walls with wet sand packed between them, topped with a damp cover, turn evaporation into cooling: the inside runs 10–15 °C below outside at around 90% humidity, enough to slow wilting and spoilage and give vegetables and fruit several more days of shelf life — with no electricity and almost no running cost.
This tool sizes the build for you: the chamber footprint, the number of crates, the holding capacity in kg, the water needed per day and the bricks required from your produce load and crate size. Use it to plan a low-cost cool store for short-term holding between harvest and market. Pair it with the Cold Storage Capacity, Cold Storage Shelf-Life and Storage Loss calculators to plan your whole post-harvest chain.
No power needed
Evaporation cools it — works fully off-grid.
Plan the build
Footprint, bricks and capacity before you start.
Extend shelf life
A few extra days for leafy and soft produce.
Know the water
Daily water to keep the sand and cover wet.
Frequently Asked Questions
What is an evaporative cool chamber?+
It is a zero-energy cool store — also called a Pusa cool chamber — built as a double brick wall with wet sand packed between the two walls. As water evaporates from the sand and a wet top cover, it draws heat from inside, dropping the chamber temperature 10–15 °C below outside and holding around 90% humidity, all with no electricity.
How is the chamber sized?+
The number of crates = produce load ÷ crate weight. The crates are stacked, and that stack sets the inside footprint of the chamber; the calculator works out a practical floor area to hold them. From the footprint it estimates the bricks for the double wall and the holding capacity in kilograms of produce the chamber will take.
How much can it cool?+
A well-built, kept-wet chamber typically runs 10–15 °C cooler than the outside air and holds roughly 90% relative humidity. The drier, hotter and breezier the weather, the more evaporation and the bigger the temperature drop. It will not match a refrigerated cold room, but it dramatically slows wilting and spoilage of fresh produce.
How much water does it need?+
The sand cavity and the top cover must be kept continuously moist, so the chamber needs water once or twice a day, more in hot, dry, windy conditions when evaporation is fastest. The calculator estimates the daily water need from the chamber size; in practice top it up whenever the sand starts to dry out.
What produce is it best for?+
It is ideal for short-term holding of leafy greens, soft vegetables, tomatoes, and many fruits — keeping them fresh and crisp for a few extra days between harvest and market. It is not meant for long-term storage or for produce that needs near-freezing temperatures; for that you still need refrigerated cold storage.
What materials do I need to build one?+
Mainly bricks for the inner and outer walls, river sand to fill the cavity, a frame and a cover (often bamboo or cane with sacking) kept wet on top, and a steady water source. The calculator gives the brick count and footprint; the design is deliberately simple and cheap so a farmer can build it on-site.
Why a double wall with sand between?+
The sand-filled cavity holds water and provides a large evaporating surface all around the produce, so cooling is even on every side rather than just the top. The inner wall stays cool and damp, the outer wall shields from direct sun, and the wet sand between is the engine that keeps the inside cool as long as it is kept moist.
Does it need electricity or a fan?+
No — that is the whole point. A basic Pusa cool chamber is fully passive: evaporation does the cooling, so it works off-grid and costs almost nothing to run. The only input is water and the labour to keep the sand and cover wet. Some larger versions add a small drip or sprinkler to automate the wetting.
How big a stack and footprint will I get?+
Enter your produce load and the weight per crate; the tool gives the number of crates, the resulting chamber footprint and the holding capacity. Keep the stack a sensible height for loading and airflow, and leave a little working space — treat the footprint as the inside floor area the crate stack needs.
Are the figures exact?+
They are sound planning figures for sizing and materials. The crates and capacity follow directly from your load and crate weight, while the footprint, bricks and water are practical estimates. Real cooling depends on climate, build quality and how diligently you keep it wet, so treat the temperature drop as a typical range, not a guarantee.