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Tech Tips:

Set Inverter Technology Up for Success in Humid Climates

This tech tip about humidity control, particularly as it relates to VRF systems and others that use inverter technology, is a companion piece to a podcast episode with Roman Baugh. You can listen to that podcast episode HERE. Those of you who work in humid climates and install or repair ductless systems are probably well […]

The 3 Fan Laws and Fan Curve Charts

This article was written by Tim De Stasio with Southern Comfort Consulting and Service. It was originally published on his blog, which you can access by clicking THIS link, but he permitted us to republish it on HVAC School as well. Thanks, Tim! It is critical for an HVAC technician to understand airflow and how […]

Blowers, Props, and How They Behave (or Misbehave)

Fan laws and fan curves are a deep subject with a lot of nuance and variation. Just to get our heads around the subject, let's focus on two different types of fans that we see all the time in HVAC: the prop/axial type and the radial/centrifugal type. Centrifugal/Radial As we increase the pressure differential across […]

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How to Evacuate an AC system, Full Vacuum Procedure

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HVAC School – For Techs, By Techs

Real training for HVAC ( Heating, Ventilation, Air Conditioning and Refrigeration) Technicians. Including recorded tech training, interviews, diagnostics and general conversations about the trade.

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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Absorption Cooling – The Rise and Fall and Rise – Short #272

12/30/2025

Bryan Orr

Combustion Analysis w/ Tony G.

12/25/2025

Bryan Orr