What did early studies of temperature and humidity reveal for heating and air-conditioning design?

Early studies in the field of HVAC design revealed that controlling both temperature and humidity is essential for creating comfortable and functional indoor environments. A pivotal moment occurred in 1902 when Willis Carrier addressed a specific industrial challenge: high humidity was causing magazine pages to wrinkle during the printing process. By cooling the air, he discovered that it would lose moisture, leading to the development of systems that could automatically regulate both temperature and humidity.1

These early findings highlighted that air-conditioning is not merely about cooling; it is the active control of moisture content, as cool air holds less water vapor than warm air. Furthermore, research into human comfort demonstrated that relative humidity alone is an imperfect metric because it is highly dependent on temperature. While relative humidity is often used in weather reporting, the dew point temperature—the point at which air becomes saturated—is a more accurate indicator of how comfortable air will feel to people, particularly as temperatures rise above 21 °C (70 °F).123