Evaporative Cool Chamber & A Cool Store With No Power

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.