From The Economist's Babbage blog:
AS AMERICANS endure yet another heatwave, their sole
consolation is that it might have been worse were it not for Willis
Carrier. Precisely 110 years ago in Brooklyn, on July 17th 1902, in the
middle of a warm and wet summer, Carrier signed off on the final
drawings of what within a few weeks became the world's first modern
air-conditioning unit. It was not designed to waft a merciful chill to
the perspiring masses. Rather, the bulky device was intended to regulate
humidity at a printing plant. Improving workers' comfort was a
side-effect. It was not until the 1930s that air conditioners became
widespread in offices and apartment buildings; it took another two
decades before they were common in detached homes. The latest
developments in the technology are also gracing industrial spaces to
start with.
The first active cooling systems date back to the
1840s, and relied on air blown over stored ice or pipes containing
pressurised liquid that absorbed heat. Their aim was indeed to cool
interiors (sometimes to freezing for food storage). In printing,
however, moisture is key. Paper shrinks, expands and warps in response
to changes in humidity. Keeping the amount of moisture constant was
crucial, especially in full-colour printing, which requires four passes
of the same sheet (one for each of the component colours—cyan, yellow
and magenta—and another for black). One firm, Sackett & Wilhelms of
Brooklyn, was so tired of having to bin stacks of poorly matched
magazine pages that it hired Buffalo Forge Company to fix the problem.
Buffalo put the young Carrier, considered something of a whiz kid, on
the task.
Carrier figured out that moisture could be extracted from the air by
having a system of coiled pipes. Half of the coils were kept inside the
building, under low pressure. The other half remained outside the walls.
The difference in pressure in the closed loop was maintained using a
compressor. The warmer air surrounding the indoor coils heated the
refrigerant, picked to boil at a low temperature, converting it from a
liquid to a gas. The laws of physics dictate "phase changes" like this
absorb heat, cooling the pipes. The moisture in the air surrounding the
pipes would condense onto the coils and drip into a drain. The
now-gaseous refrigerant passed through a compressor that turned it back
into a liquid. The obverse of the physical law is that heat is created
in doing this. But the warm, reliquified refrigerant radiates it while
passing through the outside set of coils. Heat is conserved, but
redistributed from the building's interior to the exterior. Finally, the
gas passed through a compression joint which lowered its pressure—and
thus temperature—allowing the process to begin anew. (Refrigerators work
the same way, and heat pumps provide warmth thanks to a reverse
process.)...MORE
