In 1902, Willis Carrier set out to fix a printing problem. He ended up inventing modern air conditioning

Willis Carrier did not set out to invent air conditioning so people could escape the summer heat. In 1902, the 25-year-old engineer working for Buffalo Forge Company was trying to solve a humidity problem at a printing plant in Brooklyn, New York. Changes in moisture were affecting the paper and ink used for colour printing, making it difficult for the company to produce consistent results.

The problem emerged at the Sackett-Wilhelms Lithographing and Publishing Company, where paper expanded and contracted as humidity levels changed. That movement made it harder to align different colours on the same sheet, while excess moisture also interfered with the ink. For the printing company, controlling humidity was therefore a production necessity rather than simply a matter of workplace comfort.

On July 17, 1902, Carrier completed the drawings for a system that could regulate the moisture in the air. His solution would become the foundation of the first modern air-conditioning system.


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How Carrier’s system controlled humidity

Carrier's equipment moved air across coils containing cold water. When warm, humid air came into contact with the cold coils, moisture condensed out of the air. The resulting air was cooler and contained less moisture.

The key innovation was therefore not simply lowering the temperature. Carrier was controlling the amount of moisture in the air. The system installed at the printing plant was designed to maintain relative humidity at about 55 per cent.

The equipment was installed during the summer of 1902. An ammonia compressor was added the following spring to meet the demands of a full summer of operation. The system worked, making the paper more stable and allowing the printing process to operate more reliably.

From a printing solution to industrial air conditioning

The cooling effect of Carrier's system soon revealed another potential use. Although keeping workers comfortable was not the original objective, removing moisture from the air also reduced the temperature inside the printing room.

Carrier subsequently developed systems for other industries where temperature and humidity were important. Textile mills became some of the early users because changes in humidity could affect manufacturing processes, and other industries eventually adopted the technology.

Carrier's work was supported by calculations involving dew point control. He used a circular calculating instrument, or slide rule, whose scales could be carefully aligned to perform precise calculations. Carrier's slide rule was patented in 1881 and manufactured by Kueffel & Esser.

The patent that became a building block of modern air conditioning

Carrier applied for a patent for his invention, titled "Apparatus for Treating Air". The patent, No. 808897, was issued on January 2, 1906.

The invention was the world's first spray-type air-conditioning equipment, capable of washing air as well as humidifying or dehumidifying it. It provided an important building block for the development of modern air conditioning.

In July 1906, Buffalo Forge Company sold Carrier's "Apparatus for Treating Air" to Chronicle Cotton Mills in Belmont, North Carolina. The system was applied to the mill's fan-heater ventilating system and became the first industrial "central station" humidifying system.

Air conditioning moves beyond factories

The technology gradually began moving towards applications beyond industrial production. In 1904, mechanical cooling was used at the St. Louis World's Fair, giving members of the public an early experience of cooled indoor air.

Carrier's early machines were large industrial systems, while residential air conditioning took much longer to become practical. In 1913, Carrier engineers sold a residential air-conditioning system to Charles Gates for his mansion in Minneapolis, although Gates died before the house was occupied.

By 1928, Carrier had developed a smaller "unit air conditioner" intended for retail shops requiring up to 2,500 cubic feet per minute of air. The first such unit was sold to Merchants Refrigerating Company for controlling conditions inside its egg storage room in Newark, New Jersey.

Air conditioning also reached transportation. In 1931, the M.V. Victoria, a 13,400-ton Italian motorship designed to operate between Italy and Egypt, became the first vessel to make its maiden voyage equipped with Carrier air conditioning.

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When cooling became about comfort

The use of air conditioning for human comfort developed more slowly than its industrial applications. In the 1920s, improved systems began appearing in theatres, where maintaining comfortable indoor temperatures became a commercial opportunity.

Smaller and cheaper systems took decades to develop. After the Second World War, air conditioning became increasingly available in homes, and its purpose in the public imagination shifted.

What began as an effort to prevent paper from expanding and contracting in a Brooklyn printing plant eventually became a technology associated with escaping summer heat. Carrier's original challenge was humidity, while the cooling of people emerged as one of the most familiar consequences of his invention.