Trace air conditioning back in time and we’d arrive in Egyptian halls ruled by the Pharaohs. We’d travel to ancient banquet halls lorded over by Mediterranean royalty. Desperate to stay cool, these rulers instructed their architects to design structures with rudimentary tunnels and stone ducts, channeling fresh air into their palaces. Eventually, additional stages brought the temperature of the hot desert air down further, with Persian, Roman, and Chinese men of knowledge passing hot air across clay and brick assemblies filled with cold water. Air conditioning was born, but it was the most passive and primitive form of climate control.
Amazingly, little changed in this model of AC for the next thousand years. Cleverer ways of moving air across cool running water and ice kept the rich cool, but it wasn’t until the dramatic introduction of mechanical components that air conditioning moved to the fore, becoming an active system of cooling. The secret, today as it was millennia ago, is heat exchange, finding a way to efficiently transfer the heat of the incoming air with the help of coolness from another system. The key concept in achieving this exchange came from compressing ammonia. Drop the temperature of ammonia to the point it became a liquid, evaporate it and allow it to condense, and the initial concept of modern air conditioning began to take shape. And all that was required was a sound understanding of cooling through evaporation, an observation made by Benjamin Franklin.
The components were all in place by the start of the twentieth century. A mechanical compressor shifted the state of a coolant, converting it into a liquid, and, as the coolant evaporated, heat transfer took place, cooling circulating water or directly cooling the air. The combination of mechanical compressors and evaporative components added a large electrical fan to forcefully draw air into ducts, across the condenser coils and begin the heat exchange magic. At first, these early units were used as much for humidity control as for keeping rooms cool. The growing textile industry especially depended on climate-controlled air for stopping yarn from splitting and snapping.
Today’s air conditioning systems have long since switched out ammonia for chlorofluorocarbons, CFC’s, in turn replacing these chemicals when it was discovered how deleterious they were, damaging our irreplaceable ozone layer. Filters, thermostats, multi-zone control, air conditioning is an essential part of human comfort, adding heating for yearlong temperature control.