Ceramic evaporative cooling modules for hot-dry public spaces

Mechanism

Fired terracotta wicks water through its body and holds a thin film at the surface. When warm air passes over wet ceramic, evaporation draws latent heat from the air, cooling it — the same physics as sweating skin or a traditional clay matka/botijo. Modern versions optimise ceramic geometry (maximising wetted surface area per volume) with CFD modelling and 3D printing, and add a small solar-powered fan and pump to drive airflow and maintain surface wetness.

A hard physical ceiling governs the approach: evaporative cooling cannot cool air below its wet-bulb temperature. The achievable drop — the "wet-bulb depression" — is large in hot, dry air and negligible in humid air.

Where it fits

This is point-of-use thermal comfort, not area cooling. It belongs as climate-adaptive street furniture and façade elements — bus/tram stops, plazas, schoolyards, courtyards, transit shelters — in hot, dry climates. It is refrigerant-free, runs on little or no grid energy, and is buildable from a local, low-carbon material by local potters. It complements canopy, albedo and passive-design solutions; it does not substitute for shade trees, but unlike trees it works immediately.

Operating profile

Measured drops vary considerably with conditions:

• CoolAnt "Beehive" (India, real deployment): 6–8 °C ambient drop at >40 °C; up to ~15 °C in best-case low-humidity conditions (operator-recorded).
• Bloc° (Zurich, design-stage prototype): up to 9 °C local drop; ~56 L water/day on days above 30 °C, partly offset by ~24 L/day rainwater harvested from a funnel roof; ~200 Wh/day solar powers the fan and pump.
• Student bench-scale terracotta unit (India): ~1.5 °C — illustrating how quickly the effect shrinks under poor conditions or weak airflow.

Costs are low (clay, a fan, a pump, a small PV panel). Best deployed where a sustainable water source exists — ideally harvested rainwater or recycled greywater rather than potable mains.

Limits

• Humidity: the effect collapses in humid air — this is the binding constraint on where it can be used.
• Water: demand peaks in the hot, dry places where water is already scarce.
• Maturity and material: terracotta is fragile, prone to cracking and mineral scaling, and requires continuous wetting; several headline designs remain studio or exhibition prototypes rather than street-hardened products.
• Scale: every figure above is the drop at the module. The honest claim is a comfort pocket, deployed in numbers — not city-scale cooling.