DIY absorption refrigerator runs on fire, salt and minimal solar power

Greenhill Forge has built a heat-driven absorption refrigerator that uses water and road salt as its working fluids instead of conventional refrigerants. The system boils a saltwater solution with fire, condenses the vapor, then evaporates it under low pressure to absorb heat from the cooled space. A small solar panel or battery powers only the pumps and fans. In initial tests, the unit reached approximately 5°C with 16°C ambient temperature—below typical refrigerator targets but demonstrating the concept with minimal infrastructure.

How the salt-and-fire cooling loop works

• Generator loop: Fire heats a tank of water mixed with road salt; boiled water travels up a tube to the condenser
• Condenser to absorber: A partially opened valve allows water to drip into the low-pressure absorber section, where it boils rapidly at reduced pressure and absorbs heat
• Vapor removal loop: A shower of salt solution captures the water vapor and moves it away from the cooled area
• Electrical demand: Small solar panel or battery sufficient for pumps and fans only; bulk energy input is thermal from the fire
• Performance: ~5°C achieved at ~16°C ambient in first tests; short of standard refrigerator temperatures but functional proof-of-concept
• Monitoring: Temperature and pressure sensors added for system control and observation

Why it matters

The design offers a path to refrigeration without dependence on compressed gases or significant electrical infrastructure, potentially relevant for off-grid and resource-constrained settings. The use of common materials (road salt, water) and low-tech fabrication may make replication more accessible than conventional absorption systems requiring ammonia or lithium bromide.