Invention of Air Conditioner: History of Indoor Cooling Systems

System Evolution Record

How Indoor Cooling Became a System

Trace how refrigeration, humidity control, air distribution, compact equipment, and safer refrigerants converged in indoor cooling.

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Refrigeration precursor

Gorrie's Artificial Ice Machine

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Medical purpose

Florida physician John Gorrie sought mechanical cooling for fever wards, where blocks of ice could cool air delivered to patients.

Recorded machine

U.S. Patent 8,080, granted on May 6, 1851, described compressing air, removing compression heat, and using expansion to produce refrigeration and ice.

Unfinished transition

Gorrie’s apparatus demonstrated artificial cold, but it did not supply the measured temperature, humidity, filtration, and circulation later associated with air conditioning.

Mechanical refrigeration made indoor cooling possible, but cold production alone did not create a controlled indoor climate.

Credit depends on the definition: artificial refrigeration, comfort cooling, humidity control, a named air-conditioning process, and affordable home equipment appeared at different dates.

The modern air conditioner emerged when mechanical refrigeration was joined to measured humidity control, forced-air circulation, filtration, and automatic regulation. Willis Carrier’s 1902 printing-plant system is widely treated as the first scientifically designed modern air-conditioning installation, but it was neither the first machine to make cold nor the first attempt to cool an occupied room. John Gorrie, Hermann Rietschel, Alfred Wolff, Stuart Cramer, refrigeration manufacturers, control engineers, and later appliance makers each solved a different part of the indoor-cooling problem.

Historical question	Best-supported answer
Early U.S. mechanical-cooling patent	John Gorrie’s ice and refrigeration machine, U.S. Patent 8,080, granted in 1851
Early calculated comfort-cooling systems	Hermann Rietschel’s published methods in 1894 and Alfred Wolff’s major installations around 1899–1901
Modern scientific air-conditioning milestone	Willis Carrier’s 1902 humidity-control system for Sackett & Wilhelms in Brooklyn
Carrier’s early apparatus patent	U.S. Patent 808,897, filed in 1904 and granted in 1906
Origin of the term “air conditioning”	Stuart Cramer used it in a patent application filed in April 1906
Practical large-building compressor	Carrier’s centrifugal refrigeration compressor, publicly demonstrated in 1922
Early window-room unit	H. H. Schultz and J. Q. Sherman’s 1931 design; marketed from 1932

Why Cooling a Room Was Hard

Before powered refrigeration, buildings relied on shade, thick walls, cross-ventilation, fans, nighttime air, stored ice, and water evaporation. These measures could reduce heat exposure, yet their performance followed the weather. Evaporative cooling works best when outdoor air is dry; in humid air, water evaporates slowly and adds little cooling. Ice could absorb heat, but someone had to harvest, transport, store, and replace it.

Mechanical refrigeration changed the available temperature range. A machine could move heat from a cold region to a warmer environment instead of waiting for winter ice. That solved only part of the room problem. An occupied building continuously gains heat through roofs, walls, windows, lights, machinery, people, and incoming outdoor air. Moisture enters with ventilation and infiltration and is also released indoors. A usable system had to handle these changing loads without creating drafts, wet surfaces, or unstable humidity.

John Gorrie’s cooling experiment

In the 1840s, physician John Gorrie pursued artificial refrigeration while treating patients in Apalachicola, Florida. His machine compressed air, rejected the heat created during compression, and then expanded the air to obtain a refrigerating effect. The resulting cold could make ice for cooling hospital rooms. His 1851 patent documented a working route to artificial ice and “general refrigeratory purposes,” but his project did not become a commercial indoor-climate industry.

Gorrie still matters because his work connected mechanical refrigeration with human comfort and health. It also shows why “who invented air conditioning?” has more than one defensible answer: making ice, cooling air, controlling moisture, and selling a self-contained room appliance are different accomplishments.

From Mechanical Cold to Controlled Air

Rietschel and Wolff made cooling calculable

By the late nineteenth century, refrigeration plants already served breweries, cold stores, and ice makers. Fan-driven heating and ventilation systems also moved large volumes of air through coils and ducts. Combining these trades seemed straightforward, but designers lacked dependable methods for calculating room heat gains and moist-air changes.

German engineer Hermann Rietschel addressed room cooling in an 1894 heating and ventilation text. His treatment included solar exposure, heat from occupants and lights, recirculated air, cooling-coil area, condensation below the dew point, and the energy required to remove moisture. Alfred Wolff applied related engineering methods to large American projects, including Cornell Medical College in 1899 and the New York Stock Exchange in 1901. These installations predated Carrier and demonstrate that comfort cooling already had several technical lineages.

Carrier connected humidity to process control

In 1902, the Buffalo Forge Company assigned Willis Carrier to a problem at the Sackett & Wilhelms Lithographing and Publishing Company in Brooklyn. Paper expanded and contracted as humidity changed, shifting sheets between color passes and spoiling registration. Carrier designed a system that used cooling coils and forced air to control moisture.

The first installation was an experiment rather than a finished consumer product. An ASHRAE historical study reports that the initial retrofit did not hold its intended conditions and was removed. Carrier continued testing. He developed spray-type air washers, studied the relation between dry-bulb temperature, wet-bulb temperature, dew point, and heat content, and pursued automatic control of the air’s dew point.

Carrier filed his “Apparatus for Treating Air” application on September 16, 1904; U.S. Patent 808,897 was granted on January 2, 1906. A separate dew-point-control patent followed in 1907. In 1911, his “Rational Psychrometric Formulae” helped engineers calculate moist-air processes consistently. That body of work made air treatment easier to design for a target condition rather than adjust by trial and error.

Cramer gave the field its name

Textile engineer Stuart W. Cramer worked on humidity control because moisture affected fibers and mill production. His April 1906 patent application described a “humidifying and air-conditioning apparatus,” and he used the term in a paper the following month. His equipment could mix indoor and outdoor air, spray water into the airstream, and regulate factory conditions. The name therefore arose from industrial air treatment, not from a household cooling advertisement.

How a Vapor-Compression Air Conditioner Works

Most modern room, split, and central air conditioners use a closed vapor-compression loop. The refrigerant does not create cold or get consumed during normal operation. It circulates while changing pressure and state, allowing the equipment to absorb heat indoors and reject it outdoors. Electricity powers the compressor, fans, controls, and auxiliary components.

1. Indoor heat absorptionLow-pressure refrigerant enters the evaporator coil. Indoor air passes over the cold coil, transferring heat into the refrigerant and causing it to boil.
2. Moisture removalIf the coil surface is below the air’s dew point, water vapor condenses on the coil and drains away. This lowers indoor humidity as well as temperature.
3. Vapor compressionThe compressor raises the refrigerant vapor’s pressure and temperature so it can release heat to warmer outdoor air.
4. Outdoor heat rejectionA fan moves outdoor air across the condenser. Refrigerant gives up indoor heat plus compressor energy and condenses into a high-pressure liquid.
5. Pressure reductionAn expansion device meters the liquid refrigerant into the evaporator. Its pressure and temperature fall, preparing it to absorb indoor heat again.

A thermostat compares room temperature with the set point and calls for cooling, but good control extends beyond switching a compressor on and off. Blower speed, compressor capacity, expansion-device position, outdoor conditions, and coil temperature affect both comfort and energy use. Variable-capacity equipment can run longer at lower output, often giving humidity more time to condense from the airstream.

The Parts That Turn Cooling into a Building System

Part	Function	Why it mattered historically
Compressor	Circulates refrigerant and raises vapor pressure	Smaller, quieter, and more efficient compressors widened the range of viable installations
Evaporator	Absorbs indoor heat and condenses moisture	Coil design joined cooling and dehumidification in one air path
Condenser	Rejects collected heat outdoors or to cooling water	Separating heat rejection from the occupied room made sustained indoor cooling possible
Expansion device	Meters refrigerant and creates the low-pressure side	Automatic metering improved stability under changing loads
Fans and air handler	Move air across coils and through the room or duct network	Forced-air heating and ventilation hardware supplied an existing distribution model
Filter and drain	Capture particles and remove condensate	Cooling wet coils safely required planned drainage and routine air-path maintenance
Controls and sensors	Regulate temperature, humidity, capacity, and operating sequence	Measured feedback replaced continuous manual adjustment

The placement of these parts defines the equipment family. A window unit puts nearly everything in one cabinet, with a partition between the indoor and outdoor sides. A split system connects an outdoor compressor-condenser to one or more indoor coils through refrigerant piping. A central system adds an air handler and duct network. Large buildings may use a chiller to cool water, pumps to distribute that water, and separate air-handling units for different zones.

From Factories and Theaters to Homes

Centrifugal chillers expanded the scale

Early large refrigeration plants commonly used reciprocating compressors, whose pistons compressed refrigerant in cylinders. Carrier’s practical centrifugal machine used a rapidly rotating impeller to accelerate refrigerant vapor and convert that velocity into pressure. The Smithsonian records a public demonstration on May 22, 1922. The design offered high capacity in a form suited to large installations.

Factories had an economic reason to buy climate control: stable temperature and humidity improved processes involving paper, textiles, tobacco, film, food, and precision goods. Public venues created a different market. Department stores and movie theaters could attract customers during hot weather, while offices, hotels, and hospitals could condition larger occupied areas. Air conditioning was becoming a building service rather than a machine beside a production line.

Room units reduced installation work

A central plant required space, pipes or ducts, skilled design, and a large budget. The room air conditioner compressed the same thermodynamic loop into a factory-built package. According to the U.S. Department of Energy’s historical timeline, H. H. Schultz and J. Q. Sherman filed a window-ledge unit patent in 1931; units went on sale in 1932 but remained expensive. By 1947, compact lower-cost models had reached annual U.S. sales of 43,000.

Postwar manufacturing, suburban construction, improved electric service, and purpose-designed duct systems helped central cooling spread. The change was gradual and uneven: climate, income, electricity prices, building type, and construction practices all affected adoption. In the United States, the share of homes using air conditioning rose from about 57% in 1980 to about 89% in 2020, while central-system use rose from 27% to 67% over the same span.

Room, Split, Central, and Chilled-Water Designs

System family	Equipment arrangement	Typical strength	Main constraint
Window or through-wall	Indoor and outdoor sections share one cabinet	Low installation complexity for one room	Noise, opening size, appearance, and limited coverage
Portable	Room cabinet rejects heat through one or two hoses	Can be moved and requires no permanent outdoor unit	Lower practical efficiency and room-air pressure effects in many single-hose models
Ductless mini-split	Outdoor unit connects to one or more indoor fan coils	Zoned control without full-size ducts	Refrigerant piping, condensate routing, and an indoor unit in each served zone
Ducted central	Outdoor condenser serves an indoor coil and blower connected to ducts	Whole-building distribution and centralized filtration	Duct leakage, space requirements, and losses in hot unconditioned areas
Packaged rooftop	Major components sit in one outdoor cabinet linked to ducts	Consolidated service access for many low-rise commercial buildings	Weather exposure and duct-distribution losses
Chilled-water	Central chiller cools water sent to air handlers or fan coils	Large-building capacity and zoning flexibility	Pumps, water treatment, controls, plant space, and specialist operation

A heat pump uses the same components but adds valves and controls that can reverse the refrigerant flow. In cooling mode it moves heat outdoors like an air conditioner; in heating mode it extracts heat from outdoor air and releases it indoors. “Heat pump” therefore describes a reversible system, not a separate cooling principle.

Refrigerants Changed the Design Problem

A refrigerant must boil and condense at useful temperatures and pressures, carry heat efficiently, remain compatible with metals, seals, and lubricants, and stay stable through many cycles. No fluid satisfies every goal without trade-offs. Early systems used substances including ammonia, sulfur dioxide, carbon dioxide, methyl chloride, and hydrocarbons. Some performed well but posed toxicity, flammability, high-pressure, or materials problems.

Chlorofluorocarbon refrigerants, beginning commercially with R-12 in 1931, appeared to solve much of the immediate safety and stability problem. Their chemical stability later proved environmentally damaging: after release, CFCs can persist long enough to carry ozone-depleting chlorine into the stratosphere. The 1987 Montreal Protocol began the international phaseout of CFCs, and later controls covered HCFCs such as R-22.

Many systems then adopted HFCs, which do not deplete stratospheric ozone. Some widely used HFCs have high global-warming potential, however. Current transitions therefore favor lower-GWP HFC blends, hydrofluoroolefins, carbon dioxide, ammonia, hydrocarbons, and other options where equipment design and safety standards permit. The suitable choice varies by equipment size, location, pressure, charge, flammability class, service system, and local rules.

What Indoor Cooling Changed

Industrial air conditioning first protected processes and products. Paper dimensions stayed steadier during color printing. Textile fibers could be worked under controlled moisture conditions. Film, tobacco, food, pharmaceutical, electronics, and precision-manufacturing operations gained tighter environmental limits. In these settings, cooling was often secondary to humidity or contamination control.

Comfort cooling changed when and where enclosed buildings could be used. Theaters and shops could remain attractive during hot weather. Offices could support dense occupancy and heat-producing equipment. Hospitals gained controlled environments for selected wards, operating areas, laboratories, and storage, although ventilation, filtration, pressure control, and infection-control design extend far beyond ordinary comfort AC.

Residential cooling affected building form as well as appliances. Builders could plan whole-house ducts, reduce reliance on operable windows, and market homes in hotter regions. Yet the effect was not uniform across countries or climates. Cost, electric-grid capacity, construction quality, and access to service still determine who receives dependable cooling.

Efficiency, Humidity, and the Remaining Limits

An air conditioner’s rated efficiency does not describe the whole building. Solar gain through glass, air leakage, weak insulation, duct leakage, dirty heat exchangers, obstructed airflow, poor controls, and incorrect refrigerant charge can all raise energy use or reduce capacity. Shading, an efficient building envelope, sealed ducts, and suitable equipment sizing reduce the cooling load before the compressor has to meet it.

Oversizing creates a less obvious problem in humid climates. A large single-speed unit may lower room temperature quickly and then stop before enough air has passed over the cold coil to remove moisture. The room can feel cool but damp. Longer low-capacity operation, correct airflow, and separate dehumidification where needed can give better moisture control than repeated short cycles.

Air conditioning also moves heat outdoors and shifts electricity demand toward hot periods. Future systems must supply life-protecting cooling during heat events while using less power, leaking less refrigerant, and working with grids that face sharp summer peaks. Better compressors, variable-speed drives, controls, thermal storage, heat-pump operation, low-impact refrigerants, and buildings with lower heat gain address different parts of that task.

Questions People Ask About Air Conditioners

Who invented the modern air conditioner?

Willis Carrier receives the usual credit because his 1902 work joined mechanical cooling with scientific humidity control and led to repeatable engineering methods. That credit does not erase earlier refrigeration and comfort-cooling work by Gorrie, Rietschel, Wolff, and others.

Was Carrier’s 1902 system made for home comfort?

No. It addressed humidity at a Brooklyn printing plant so paper dimensions and color registration would remain stable. Comfort cooling became a larger market later.

Why does an air conditioner produce water?

Warm indoor air can hold water vapor. When that air touches an evaporator surface below its dew point, some vapor condenses into liquid. A drain pan and line carry the condensate away.

Does an air conditioner bring in fresh outdoor air?

Many window, split, and residential central systems mainly recirculate indoor air. Required outdoor ventilation may come from a separate intake or ventilation system. Cooling, circulation, filtration, and ventilation should not be assumed to be the same function.

Is a bigger air conditioner better?

No. Equipment should match the building’s calculated heat and moisture loads. Oversized units can short-cycle, control humidity poorly, cost more, and create uneven temperatures.