How Willis Carrier Invented the Modern Air Conditioner

Willis Carrier's 1906 patent for an apparatus to control humidity and temperature, forming the technical foundation for modern air conditioning systems.

What it covers

The apparatus treats air by passing it through a spray of water to control its moisture content and temperature. By adjusting the temperature of the water spray, the system can either cool the air or remove humidity through condensation. This process allows for the precise regulation of the air's dew point, which is the temperature at which water vapor turns into liquid. The device essentially creates a controlled environment by balancing thermal and moisture levels within a stream of air.

What it doesn't cover

• —Does not cover chemical-based air purification or filtration systems.
• —Does not cover modern vapor-compression refrigeration cycles using chemical refrigerants.
• —Does not cover systems that lack a water-spray-based humidity control mechanism.

The clever bit

Carrier realized that by controlling the temperature of the water spray, he could precisely dictate the moisture content of the air, effectively decoupling temperature control from humidity control.

Why it matters

This patent marks the birth of modern climate control. It enabled industries like printing and textiles to operate regardless of weather conditions, and eventually transformed global architecture and human comfort by making indoor environments habitable in extreme heat.

Real-world examples

• 1.Industrial textile mill climate control
• 2.Early 20th-century printing press humidity regulation
• 3.Commercial HVAC systems