In this short podcast episode, Bryan goes on another history journey, retelling the story of the rise and fall and rise of absorption cooling. Some of the first HVAC/R engineers cooled buildings with fire; they used absorption refrigeration, which ran on heat instead of electricity.

In the early 1800s, French scientist Michael Faraday showed that gases like ammonia could absorb heat as they evaporated. Instead of compressing the vapor, engineers looked for a way to absorb the heat from the vapor and drive it back out. In 1859, Ferdinand Carré invented a machine that boiled ammonia, absorbed the vapor into water, and reheated the mixture to desorb the ammonia, creating a self-contained refrigeration machine powered by heat alone (including waste steam from boilers). This ammonia-water absorption machine could freeze water and chill brine, and it became popular in the 1880s.

An absorption system has an evaporator that boils refrigerant, which is then absorbed into another liquid and creates a strong solution. Heat drives refrigerant back out of the solution as a vapor, where it is then condensed back to a liquid and metered. However, while they were reliable, they were heavy, expensive, and slow to respond. In the 1920s and 1930s, the rise of practical sealed electric compression systems began replacing absorption refrigeration infrastructure. By the mid-1900s, absorption chillers were replaced in all but a few applications.

Absorption didn't completely vanish, in part thanks to Servel, which continued manufacturing absorption refrigeration systems for industrial applications and rural areas with unreliable electricity. By the 1960s, Japan and Europe refined the design with lithium bromide instead of ammonia. Absorption chillers are still present, but their complexity, maintenance demands, and poor efficiency still make them impractical for most refrigeration purposes. However, with concerns about the electrical grid and decarbonization initiatives on the rise, absorption refrigeration in hybrid systems with improved efficiency and a heat source obtained from gas turbines and biomass boilers looks promising.

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