Air conditioning

Lore & Background

Air conditioning dates back to prehistory. Double-walled living quarters, with a gap between the two walls to encourage air flow, were found in the ancient city of Hamoukar, in modern Syria. Ancient Egyptian buildings also used a wide variety of passive air-conditioning techniques. These became widespread from the Iberian Peninsula through North Africa, the Middle East, and Northern India.

Passive techniques remained widespread until the 20th century when they fell out of fashion and were replaced by powered air conditioning. Using information from engineering studies of traditional buildings, passive techniques are being revived and modified for 21st-century architectural designs. In 1558, Giambattista della Porta described a method of chilling ice to temperatures far below its freezing point by mixing it with potassium nitrate. In 1620, Cornelis Drebbel demonstrated 'Turning Summer into Winter' for James I of England.

In 1758, Benjamin Franklin and John Hadley conducted experiments applying the principle of evaporation as a means to cool an object rapidly. In 1820, Michael Faraday discovered that compressing and liquefying ammonia could chill air when the liquefied ammonia was allowed to evaporate. In 1842, Florida physician John Gorrie used compressor technology to create ice, which he used to cool air for his patients. Gorrie was granted a patent in 1851.

In 1851, James Harrison created the first mechanical ice-making machine in Geelong, Australia, and was granted a patent for an ether vapor-compression refrigeration system in 1855. In 1894, Hungarian engineer István Röck began manufacturing industrial ammonia compressors driven by electric motors. By 1896, his factory produced 'dry air cooling apparatuses' for cooling and dehumidification. In 1901, American inventor Willis H. Carrier built what is considered the first modern electrical air conditioning unit.

In 1902, he installed his first air-conditioning system in the Sackett-Wilhelms Lithographing & Publishing Company in Brooklyn, New York. He patented 'air conditioning' in 1906. In 1906, Stuart W. Cramer coined the term 'air conditioning' in a patent claim. In 1914, the first domestic air conditioning was installed in Minneapolis in the home of Charles Gilbert Gates.

From Ammonia to Solar Thermal – The Long Arc of Absorption Cooling

In the late 1800s, engineers tackling the challenge of mechanical cooling relied on a mixture of ammonia and water as the working fluid in absorption systems. The basic principle was elegant: heat one end of a network of expansion and condensation pipes, and the opposite end would chill enough to form ice. At that time, natural gas served as the thermal driver.

Over the decades, the chemistry evolved—lithium bromide paired with water became another widely adopted combination—while the heat source shifted as well. Propane now powers the absorption chillers found in recreational vehicles, and hot-water solar thermal collectors have emerged as what some describe as a free-energy heat input for modern installations. This trajectory, from fossil-fueled heating to sun-driven thermal input, represents a quiet but significant reorientation of how absorption cooling sources its energy.

DC-Powered Mini Splits and the Non-Compressor Frontier

A new generation of photovoltaic air-conditioning heat pumps now runs entirely on direct current, eliminating the conversion steps that plagued earlier designs. One mini-split variant taps a 48-volt DC bus and a small battery array—typically four 12-volt cells in series—dedicated solely to the cooling unit, allowing it to keep running at night or under cloud cover.

Both employ variable refrigerant flow technology with high-efficiency variable-speed DC motors and compressors, demanding very little run power while also delivering heating. For larger commercial buildings, a third VRF-based configuration adds grid and battery backup plus optional net metering, and can simultaneously heat one zone and cool another from a single outdoor unit. Beyond compressors entirely, phase-change indirect evaporative coolers now achieve SEER ratings above 20 and up to 40 in dry climates, needing only a circulation fan and a water supply, as demonstrated at facilities like McCarran Airport in Las Vegas.

Reader's Guide

Air conditioners, which typically use vapor-compression refrigeration, range in size from small units used in vehicles or single rooms to massive units that can cool large buildings. Air source heat pumps, which can be used for heating as well as cooling, are becoming increasingly common in cooler climates. According to the International Energy Agency (IEA), 1.6 billion air conditioning units were used globally in 2016. The United Nations has called for the technology to be made more sustainable to mitigate climate change and for the use of alternatives, such as passive cooling, evaporative cooling, selective shading, windcatchers, and thermal insulation.

Did You Know?

• An estimated 190,000 heat-related deaths are averted annually owing to air conditioning.
• In hot weather, air conditioning can prevent heat stroke, dehydration due to excessive sweating, electrolyte imbalance, kidney failure, and other issues due to hyperthermia.
• Historians rank air conditioning as a key factor that shaped postwar metropolitan growth, alongside highways, automobiles, shopping malls, and suburban housing.