Two Ways to Move Heat
By the middle of the 1800s, engineers knew that cold could be made by evaporating a liquid. The remaining question was how to reuse the vapor rather than let it escape. Two families of solutions emerged. In compression machines, a mechanical pump squeezes the vapor back into a liquid. In absorption machines, the vapor is dissolved into another liquid and then released by heating, so that heat does the work that a compressor otherwise would. The two methods developed side by side, and both ended up in homes.
Carré and the Absorption Machine
The French engineer Ferdinand Carré patented an absorption machine in 1859. It used ammonia as the refrigerant and water as the absorbent. In outline, ammonia dissolved in water is heated in a generator, which drives off ammonia gas. The gas is cooled and condensed, then evaporated in a separate chamber where it absorbs heat and produces cold. The vapor returns to the water in an absorber, and the cycle starts again.
Carré’s machines were valued because they could make ice using a heat source, such as a coal fire, with very few moving parts, and no need for a high-pressure compressor. Carré’s brother Edmond had earlier built a machine using other substances, so the family contribution is sometimes presented as a shared effort, though Ferdinand’s ammonia-water design is the one most associated with practical use. The machines were notably used to produce ice in the American South during the Civil War era, when supplies of northern natural ice were cut off, though the details of this are less well documented.
Linde and Industrial Compression
In Germany, Carl von Linde, a professor at the Technical University of Munich, worked on the thermodynamics of refrigeration and developed machines that used ammonia as the refrigerant in a compression cycle. His designs of the 1870s were more efficient and more reliable than earlier ether machines, and breweries bought them to keep cellars cold all year. Linde founded a company in 1879 and, in time, his work also led to methods for liquefying air.
The American engineer David Boyle also built an ammonia compression machine in the early 1870s, and other designers developed similar systems. Ammonia compression became the standard for industry, and that choice is part of the story in refrigerant gases. Because steam engines and, later, electric motors could drive compressors, the design scaled well, from breweries to cold-storage warehouses and ships.
Why Compression Won Most Markets
Compression systems offered a better ratio of cooling to energy use and could be made in a wide range of sizes. Once small electric motors and sealed compressors became available, the technology could be shrunk to household scale. By the 1920s, nearly all home refrigerators sold in North America used compression. The household refrigerators that followed are discussed in the pillar overview of the refrigerator’s history.
The Electrolux Absorption Refrigerator
Absorption cooling did not disappear. In the 1920s, two Swedish engineering students, Baltzar von Platen and Carl Munters, developed an absorption refrigerator that needed no pump. Their design used ammonia, water and hydrogen gas. Heat applied to the generator caused ammonia vapor to rise and circulate by gravity and convection, and the hydrogen allowed the ammonia to evaporate at a low total pressure. The cycle ran with no moving parts at all.
The Swedish company Electrolux acquired the invention in the mid-1920s and sold the refrigerators in many countries. The units could run on a gas flame, kerosene or electricity. Their virtues were silence, long life and independence from the electrical grid, which mattered in rural areas and places without reliable power. They were less efficient than compression units, and they gradually lost share in homes as electric service expanded. They remain in use today for some caravans and recreational vehicles, off-grid cabins and hotel minibars where quiet is a priority.
A related curiosity is an absorption refrigerator patented in 1930 by Albert Einstein and Leo Szilard. It used an electromagnetic pump with no moving mechanical parts, and was designed partly with safety in mind, since leaking seals in other machines had been a problem. It was not commercialized.
Comparing the Two
| Feature | Compression | Absorption |
|---|---|---|
| Main energy input | Electricity to a compressor | Heat from gas, kerosene or electricity |
| Moving parts | Compressor and motor | Often none |
| Typical efficiency | Higher | Lower |
| Noise | Audible hum | Nearly silent |
| Common uses | Most refrigerators and air conditioners | Off-grid, mobile and some industrial uses |
Absorption machines also remain important in industrial settings where waste heat is available, such as some large building cooling plants that use heat from power generation. In those cases, using heat that would otherwise be wasted can make the design attractive.
Lasting Influence
The distinction between the two approaches shows how inventors faced the same physical problem and found different answers shaped by the energy available to them. Compression eventually dominated because electricity became universal, but absorption demonstrated that refrigeration can be driven by a flame as well as a motor. The first experiments behind both families are covered under artificial refrigeration.