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An absorption refrigerator is a refrigerator that uses a heat source to provide the energy needed to drive the cooling process. Solar energy, burning a fossil fuel, waste heat from factories, and district heating systems are examples of heat sources that can be used.

An absorption refrigerator uses two coolants: the first coolant performs evaporative cooling and then is absorbed into the second coolant; heat is needed to reset the two coolants to their initial states.

Absorption refrigerators are commonly used in recreational vehicles (RVs), campers, and caravans because the heat required to power them can be provided by a propane fuel burner, by a low-voltage DC electric heater (from a battery or vehicle electrical system) or by a mains-powered electric heater. Absorption refrigerators can also be used to air-condition buildings using the waste heat from a gas turbine or water heater in the building. Using waste heat from a gas turbine makes the turbine very efficient because it first produces electricity, then hot water, and finally, air-conditioning—trigeneration.

Unlike more common vapor-compression refrigeration systems, an absorption refrigerator has no moving parts.

History

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In the early years of the 20th century, the vapor absorption cycle using water-ammonia systems was popular and widely used, but after the development of the vapor compression cycle it lost much of its importance because of its low coefficient of performance (about one fifth of that of the vapor compression cycle).[citation needed] Absorption refrigerators are a popular alternative to regular compressor refrigerators where electricity is unreliable, costly, or unavailable, or where noise from the compressor is problematic; or where surplus heat is available.

In 1748 in Glasgow, William Cullen invented the basis for modern refrigeration, although he is not credited with a usable application. More on history of refrigeration can be found in the paragraph Refrigeration Research on page Refrigeration.

Absorption refrigeration uses the same principle as adsorption refrigeration, which was invented by Michael Faraday in 1821, but instead of using a solid adsorber, in an absorption system an absorber absorbs the refrigerant vapour into a liquid.

Absorption cooling was invented by the French scientist Ferdinand Carré in 1858.[1] The original design used water and sulphuric acid. In 1922, two students at the Royal Institute of Technology in Stockholm, Sweden, Baltzar von Platen and Carl Munters, enhanced the principle with a three-fluid configuration. This "Platen-Munters" design can operate without a pump.

Commercial production began in 1923 by the newly-formed company AB Arctic, which was bought by Electrolux in 1925. In the 1960s, absorption refrigeration saw a renaissance due to the substantial demand for refrigerators for caravans (travel trailers). AB Electrolux established a subsidiary in the United States, named Dometic Sales Corporation. The company marketed refrigerators for recreational vehicles (RVs) under the Dometic brand. In 2001, Electrolux sold most of its leisure products line to the venture-capital company EQT which created Dometic as a stand-alone company. Dometic still sold absorption fridges as of July 2025.[2]

In 1926, Albert Einstein and his former student Leó Szilárd proposed an alternative design known as the Einstein refrigerator.[3]

At the 2007 TED Conference, Adam Grosser presented his research of a new, very small, "intermittent absorption" vaccine refrigeration unit for use in third world countries. The refrigerator is a small unit placed over a campfire, that can later be used to cool 15 litres (3.3 imp gal; 4.0 US gal) of water to just above freezing for 24 hours in a 30 °C (86 °F) environment.[4] The concept was similar to an early refrigeration device known as an Icyball.

Principles

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Common absorption refrigerators use a refrigerant with a very low boiling point (less than −18 °C (0 °F)) just like compressor refrigerators. Compression refrigerators typically use an HCFC or HFC, while absorption refrigerators typically use ammonia or water and need at least a second fluid able to absorb the coolant, the absorbent, respectively water (for ammonia) or brine (for water). Both types use evaporative cooling: when the refrigerant evaporates (boils), it takes some heat away with it, providing the cooling effect. The main difference between the two systems is the way the refrigerant is changed from a gas back into a liquid so that the cycle can repeat. An absorption refrigerator changes the gas back into a liquid using a method that needs only heat, and has no moving parts other than the fluids.

Absorption cooling process
1: boiler 2: separation chamber 3: ammonia-poor water back-pipe 4: ammonia condenser 5: pressure balance pipe 6: liquid ammonia pipe 7: evaporator (inside cabinet) 8: ammonia gas pipe 9: absorber (water absorbs ammonia)

The absorption cooling cycle can be described in three phases:

  • Evaporation: A liquid refrigerant evaporates in a low partial pressure environment, thus extracting heat from its surroundings (e.g. the refrigerator's compartment). Because of the low partial pressure, the temperature needed for evaporation is also low.
  • Absorption: The second fluid, in a depleted state, sucks out the now gaseous refrigerant, thus providing the low partial pressure. This produces a refrigerant-saturated liquid which then flows to the next step:
  • Regeneration: The refrigerant-saturated liquid is heated, causing the refrigerant to evaporate out.
    1. The evaporation occurs at the lower end of a narrow tube; the bubbles of refrigerant gas push the refrigerant-depleted liquid into a higher chamber, from which it will flow by gravity to the absorption chamber.
    2. The hot gaseous refrigerant passes through a heat exchanger, transferring its heat outside the system (such as to surrounding ambient-temperature air), and condenses at a higher place. The condensed (liquid) refrigerant will then flow by gravity to supply the evaporation phase.

The system thus silently provides for the mechanical circulation of the liquid without a usual pump. A third fluid, gaseous, is usually added to avoid pressure concerns when condensation occurs (see below).

In comparison, a compressor based heat pump works by pumping refrigerant gas from an evaporator to a condenser. This reduces the pressure and boiling temperature in the evaporator and increases the pressure and condensing temperature in the condenser. Energy from an electric motor or internal combustion engine is required to operate the compressor pump. Compressing the refrigerant uses this energy to do work on the gas, increasing its temperature. The warm, high pressure gas then enters the condenser where it undergoes a phase change to a liquid, releasing heat to the condenser's surroundings. Warm liquid refrigerant moves from the high pressure condenser to the low pressure evaporator via an expansion valve, also known as a throttling valve or a Joule-Thomson valve. The expansion valve partially vaporizes the refrigerant cooling it via evaporative cooling and the resulting vapor is cooled via expansive cooling. (This is a combination of Joule-Thomson cooling and work done by the expanding gas, both at the expense of the internal energy of the gas) The cold, low pressure liquid refrigerant will now absorb heat from the evaporator's surroundings and vaporize. The resulting gas enters the compressor and the cycle begins again.

Simple salt and water system

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A simple absorption refrigeration system common in large commercial plants uses a solution of lithium bromide or lithium chloride salt and water. Water under low pressure is evaporated from the coils that are to be chilled. The water is absorbed by a lithium bromide/water solution. The system drives the water out of the lithium bromide solution with heat.[5]

Water spray absorption refrigeration

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Water spray absorption system

Another variant uses air, water, and a salt water solution. The intake of warm, moist air is passed through a sprayed solution of salt water. The spray lowers the humidity but does not significantly change the temperature. The less humid, warm air is then passed through an evaporative cooler, consisting of a spray of fresh water, which cools and re-humidifies the air. Humidity is removed from the cooled air with another spray of salt solution, providing the outlet of cool, dry air.

The salt solution is regenerated by heating it under low pressure, causing water to evaporate. The water evaporated from the salt solution is re-condensed, and rerouted back to the evaporative cooler.

Single pressure absorption refrigeration

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Dometic absorption refrigerator.
1. Hydrogen enters the pipe with liquid ammonia
2. Ammonia and hydrogen enter the inner compartment. Volume increase causes a decrease in the partial pressure of the liquid ammonia. The ammonia evaporates, taking heat from the liquid ammonia (ΔHVap) lowering its temperature. Heat flows from the hotter interior of the refrigerator to the colder liquid, promoting further evaporation.
3. Ammonia and hydrogen return from the inner compartment, ammonia returns to absorber and dissolves in water. Hydrogen is free to rise.
4. Ammonia gas condensation (passive cooling).
5. Hot ammonia gas.
6. Heat insulation and distillation of ammonia gas from water.
7. Electric heat source.
8. Absorber vessel (water and ammonia solution).
Thermal image of a Dometic absorption refrigerator of a comparable type to the one in the labelled image above. Colour indicates relative temperature: blue=cold, red is hottest. The heat source (7) is contained entirely within the insulation section (6).

A single-pressure absorption refrigerator takes advantage of the fact that a liquid's evaporation rate depends upon the partial pressure of the vapor above the liquid and goes up with lower partial pressure. While having the same total pressure throughout the system, the refrigerator maintains a low partial pressure of the refrigerant (therefore high evaporation rate) in the part of the system that draws heat out of the low-temperature interior of the refrigerator, but maintains the refrigerant at high partial pressure (therefore low evaporation rate) in the part of the system that expels heat to the ambient-temperature air outside the refrigerator.

The refrigerator uses three substances: ammonia, hydrogen gas, and water. The cycle is closed, with all hydrogen, water and ammonia collected and endlessly reused. The system is pressurized to raise the boiling point of ammonia higher than the temperature of the condenser coil (the coil which transfers heat to the air outside the refrigerator, by being hotter than the outside air.) This pressure is typically 14–16 standard atmospheres (1,400–1,600 kPa) putting the dew point of ammonia at about 35 °C (95 °F).

The cooling cycle starts with liquid ammonia at room temperature entering the evaporator. The volume of the evaporator is greater than the volume of the liquid, with the excess space occupied by a mixture of gaseous ammonia and hydrogen. The presence of hydrogen lowers the partial pressure of the ammonia gas, thus lowering the evaporation point of the liquid below the temperature of the refrigerator's interior. Ammonia evaporates, taking a small amount of heat from the liquid and lowering the liquid's temperature. It continues to evaporate, while the large enthalpy of vaporization (heat) flows from the warmer refrigerator interior to the cooler liquid ammonia and then to more ammonia gas.

In the next two steps, the ammonia gas is separated from the hydrogen so it can be reused.

  1. The ammonia (gas) and hydrogen (gas) mixture flows through a pipe from the evaporator into the absorber. In the absorber, this mixture of gases contacts water (technically, a weak solution of ammonia in water). The gaseous ammonia dissolves in the water, while the hydrogen, which doesn't, collects at the top of the absorber, leaving the now-strong ammonia-and-water solution at the bottom. The hydrogen is now separate while the ammonia is now dissolved in the water.
  2. The next step separates the ammonia and water. The ammonia/water solution flows to the generator (boiler), where heat is applied to boil off the ammonia, leaving most of the water (which has a higher boiling point) behind. Some water vapor and bubbles remain mixed with the ammonia; this water is removed in the final separation step, by passing it through the separator, an uphill series of twisted pipes with minor obstacles to pop the bubbles, allowing the water vapor to condense and drain back to the generator.

The pure ammonia gas then enters the condenser. In this heat exchanger, the hot ammonia gas transfers its heat to the outside air, which is below the boiling point of the full-pressure ammonia, and therefore condenses. The condensed (liquid) ammonia flows down to be mixed with the hydrogen gas released from the absorption step, repeating the cycle.

See also

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References

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Further reading

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Absorption refrigerator

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An absorption refrigerator is a cooling device that operates using rather than mechanical compression, employing a cycle where a vapor is absorbed into a absorbent, separated by , and then re-evaporated to produce effects. This system typically utilizes working fluid pairs such as and or and , allowing it to run on low-grade sources like , , or , making it suitable for applications where is scarce or expensive. The fundamental principle of an absorption refrigerator involves four main processes: absorption, generation, condensation, and evaporation. In the absorber, the vapor (e.g., ) is absorbed into the liquid absorbent (e.g., ), releasing and forming a strong solution; this solution is then pumped to the generator, where input desorbs the refrigerant, creating a weak solution that returns to the absorber and pure refrigerant vapor that proceeds to the condenser for . The liquid refrigerant expands through a to the , where it absorbs from the cooled at low , before returning as vapor to the absorber, completing the cycle without moving parts beyond a small . Key advantages include silent operation, longevity due to minimal mechanical wear, and environmental benefits from using natural refrigerants, though it achieves a lower (COP) of 0.6–1.2 compared to vapor-compression systems (typically 3–5). Absorption refrigeration has a rich history dating back to the mid-19th century, with Edmond Carré inventing the first intermittent absorption machine in 1850 using and , followed by his brother Carré's development of a continuous ammonia-water system patented in 1860. The technology gained prominence in the early through innovations like the Einstein-Szilard pump-less design patented in 1930, which influenced absorption refrigerators still used in recreational vehicles and portable units today. Modern applications span large-scale chillers in industrial plants, solar-powered systems for off-grid cooling, and sectors leveraging , with ongoing research focusing on improving efficiency through advanced working pairs and hybrid configurations.

Fundamentals

Basic Principle

An absorption refrigerator operates on a heat-driven that achieves cooling through the absorption and desorption of a in a absorbent, without relying on mechanical compression. In this , a vapor, such as , is absorbed into a absorbent, typically , forming a solution; heat is then applied to separate the , allowing it to circulate and produce cooling effects. This process contrasts with conventional vapor-compression refrigerators, which use electrical energy to power a , by instead utilizing as the primary driver. The cycle consists of four main processes. In the generation stage, supplied to the generator causes desorption, releasing vapor from the absorbent solution. The vapor then travels to the condenser, where it cools and condenses into a , rejecting to the surroundings. Next, in the , the expands and evaporates at low , absorbing from the cooled space to provide . Finally, the vapor is reabsorbed into the weakened absorbent in the absorber, completing the cycle and preparing the solution for recirculation via a small . This mechanism enables the use of low-grade heat sources, such as , , or industrial waste heat, to drive the process, making it suitable for applications where is limited or costly. The basic includes a generator for desorption, an absorber for , a condenser for , an for cooling, and a solution pump to maintain circulation, all interconnected in a closed loop.

Key Components

The absorption refrigerator operates through a network of interconnected components that facilitate the separation, circulation, and recombination of and absorbent in a closed-loop configuration. The primary elements include the generator, absorber, condenser, , , and , each performing a specific function to enable -driven cooling without mechanical compression. The generator, often heated by an external source such as or , desorbs vapor from the absorbent- solution by elevating its , typically to 55–225°C depending on the design; the resulting (depleted of ) is then directed back to the absorber. The absorber mixes the incoming vapor with the under cooling conditions, forming a strong solution that releases to an external ; this process relies on the affinity between the and absorbent to achieve efficient absorption. In the condenser, the pure vapor from the generator is cooled—often to 25–50°C—and liquefied, rejecting to the surroundings before flowing to the . The allows the liquid to expand and vaporize at low pressure (around 0–15°C), absorbing from the cooled to produce the effect, after which the vapor proceeds to the absorber. The circulates the strong solution from the absorber to the generator, requiring minimal input compared to vapor compression systems. , such as solution heat exchangers, enhance overall efficiency by transferring between the strong and s, potentially increasing the (COP) by 44–66% through thermal recovery. Construction materials for these components are selected for compatibility with the working fluids and operational s. In ammonia-based systems, pressure vessels and piping are typically fabricated from , as ammonia is incompatible with or , ensuring durability and preventing when combined with corrosion inhibitors like sodium chromate. For water-lithium systems, corrosion-resistant alloys are employed to mitigate degradation from the hygroscopic absorbent. These components integrate into a sealed, closed-loop where the and absorbent continuously cycle without external replenishment, maintaining system integrity. A still or rectifier is often incorporated at the generator outlet to purify the refrigerant vapor by separating impurities (e.g., water in ammonia systems), preventing contamination in downstream components and improving efficiency. Safety features are essential, particularly in ammonia-based systems due to the refrigerant's and pressure risks. Pressure relief valves are standard on pressure vessels to automatically vent excess pressure, preventing ruptures and ensuring compliance with standards. Additional measures, such as excess flow valves and , may be integrated to contain potential releases.

History

Invention and Early Development

The absorption refrigerator was first invented by French engineer Edmond Carré in 1850, who developed an intermittent machine using as the refrigerant and as the absorbent. This pioneering device marked the beginning of absorption-based cooling through a chemical process, though it required manual reheating for each cycle and was limited in practicality. Building on this, Edmond's brother Ferdinand Carré developed the first practical -water absorption system in 1858. This system utilized as the refrigerant and as the absorbent, enabling more efficient production of artificial . Ferdinand Carré refined the design in the late , achieving continuous operation that reduced manual intervention and improved reliability. He secured a French for the ammonia-water machine in 1859 and a U.S. in 1860 (No. 30,201), which described an apparatus capable of producing at rates up to 200 kg per hour in industrial scales. Further enhancements in the included adaptations for greater efficiency, such as integrating agitators inspired by earlier vacuum systems to optimize fluid circulation, allowing for more automatic operation powered by external heat sources, though early versions still required some manual oversight. The technology gained public attention through demonstrations, notably at the 1867 Paris Universal Exposition, where Ferdinand Carré's apparatus was exhibited for producing artificial cold and ice, highlighting its potential for commercial applications like during the era. Despite these innovations, early absorption refrigerators faced substantial challenges, including low —often requiring excessive heat input for modest cooling output—and persistent need for manual intervention in charging and regenerating the absorbent, which hindered scalability and led to limited adoption outside specialized industrial settings by the late .

Commercialization and Modern Advancements

In the 1910s and 1920s, and Leó Szilárd collaborated on developing an innovative absorption refrigerator design that eliminated the need for mechanical pumps, addressing the noise issues associated with compressor-based systems of the era. Their partnership began after Einstein, motivated by reports of fatal accidents from leaking mechanical refrigerators, sought a safer alternative; they filed a in on December 16, 1926, followed by filings in the UK and US, culminating in US Patent 1,781,541 granted in 1930. This pump-free system relied on natural circulation driven by heat and gravity, using as the , water as the absorbent, and as an auxiliary gas to enhance without moving parts. Commercialization gained momentum in the late through Servel Inc., which licensed and produced gas-fired absorption refrigerators for household use, capitalizing on the design's quiet operation and fuel flexibility. By 1927, Servel had partnered with to manufacture these models in the , achieving widespread as they offered a reliable alternative to electric units during a period of limited . Popularity peaked in , with Servel selling millions of units before the dominance of cheaper, more efficient electric compression refrigerators in the 1940s led to a decline in . Following , absorption refrigerators experienced a revival in the 1950s and 1960s, particularly for off-grid applications such as recreational vehicles (RVs) and boats, where access to electricity was unreliable. Manufacturers like and its Dometic brand developed compact, propane-powered models that operated without external power, enabling cooling in remote settings and boosting the RV industry's growth. These units, often with capacities around 6-12 cubic feet, became standard in mobile applications by the mid-1960s due to their durability and multi-fuel compatibility. Modern advancements since the 2000s have focused on enhancing efficiency and sustainability, including integration with solar thermal systems to utilize renewable heat sources for cooling. Double-effect cycles, which employ two generators to achieve coefficients of performance (COP) up to 1.2-1.4—nearly double that of single-effect systems—have been refined for higher , particularly in large-scale chillers. Research into alternative absorbents, such as ionic liquids and biomass-derived solvents, aims to reduce toxicity and compared to traditional ammonia-water or pairs, with studies demonstrating stable performance at lower environmental impact. In the 2020s, developments in recovery have targeted data centers, where absorption systems capture low-grade exhaust heat (around 40-60°C) to drive cooling, achieving significant savings in hybrid setups and supporting sustainable operations in high-density facilities.

Thermodynamic Principles

Absorption Cycle

The absorption refrigeration cycle operates through four primary stages that facilitate cooling without mechanical compression, relying instead on to drive the separation and recombination of a -absorbent . In the generation stage, heat is supplied to the generator, inducing an endothermic desorption where the vaporizes and separates from the absorbent solution, concentrating the absorbent. This vapor is then directed to the condenser. The absorption stage follows, where the vapor, after cooling, is reabsorbed into the dilute absorbent solution in the absorber, an exothermic mixing that releases heat to the surroundings. The condensation stage involves the vapor releasing its to condense into a at higher . Finally, in the evaporation stage, the expands and evaporates at low in the , absorbing from the cooled space to produce the effect. The performance of the cycle is quantified by the (COP), defined as the ratio of the cooling provided to the total input: COP=QcQg+Wp\text{COP} = \frac{Q_c}{Q_g + W_p} where QcQ_c is the absorbed in the (), QgQ_g is the supplied to the generator, and WpW_p is the work input from the solution pump, which is often negligible compared to QgQ_g due to the low differentials. Typical COP values for single-effect systems range from 0.6 to 0.75, reflecting the cycle's reliance on rather than work. Irreversibilities in the cycle arise from processes such as non-equilibrium heat and mass transfer, mixing, and temperature gradients, leading to entropy generation that can be analyzed through the entropy balance equation for each component: ΔS=∑QT+Sgen\Delta S = \sum \frac{Q}{T} + S_{\text{gen}}, where Sgen>0S_{\text{gen}} > 0 accounts for irreversibilities, and exergy losses are given by I=T0SgenI = T_0 S_{\text{gen}} with T0T_0 as the ambient temperature. The highest entropy generation typically occurs in the generator and absorber due to the heat of mixing and separation. The cycle's pressure-temperature relationships are depicted on a temperature-entropy (T-s) , where isobars represent constant lines for the and solution paths. Standard multi-pressure operations (typically two levels) maintain low in the and absorber to enable at low temperatures, while prevails in the generator and condenser to facilitate desorption and at elevated temperatures; this setup follows isobaric processes on the T-s , with increasing during absorption and decreasing during . In contrast, single-pressure variants, such as diffusion absorption cycles, operate at uniform using an auxiliary to aid , simplifying the system but often at reduced efficiency, as shown by flatter isobars on the T-s plot. Heat exchangers play a crucial role in enhancing cycle efficiency by recovering between the hot concentrated solution leaving the generator and the cool dilute solution entering it, thereby minimizing losses from temperature mismatches and reducing the required generator heat input. These exchangers, often solution-to-solution types, operate on principles of counterflow to approach ideal , lowering overall irreversibilities by up to 20-30% in optimized systems.

Working Fluids and Their Properties

The working fluids in absorption refrigerators consist of a refrigerant-absorbent pair, where the is volatile and the absorbent has a strong affinity for it, enabling the cycle's absorption and desorption processes. The most widely used pairs are - and bromide-, selected for their thermodynamic compatibility with low-grade heat sources. - (NH₃-H₂O) operates at higher pressures, making it suitable for compact, small-scale units such as domestic or portable refrigerators. serves as the due to its low (-33°C at ) and high of vaporization (approximately 1370 kJ/kg), while acts as the absorbent with high for across a wide range (-80°C to 180°C). The pair's vapor-liquid equilibrium follows solubility curves modeled by equations like those from Patek and Klomfar (1995), showing concentrations up to 40% by weight without . However, the mixture requires rectification in the generator to remove , as residual can freeze in the and reduce efficiency; this adds complexity but allows operation down to -50°C evaporation temperatures. Regarding safety, is toxic (irritation threshold at 25 ppm) and flammable in air concentrations of 15-28%, necessitating robust containment, though its (GWP) is 0 and (ODP) is 0. Corrosivity is moderate, primarily affecting but manageable with alloys. The circulation ratio (mass flow of solution to ) is low, typically 2-10, minimizing pumping requirements while maintaining efficient . In contrast, lithium bromide-water (LiBr-H₂O) is favored for large-scale chillers operating under (evaporator pressures around 0.8-1 kPa), with as the and as the non-volatile absorbent. The solution's low , governed by Dühring's rule and models from Conde (2014), allows evaporation temperatures as low as 5°C without compression. is high up to 70% LiBr by weight, but crystallization risks occur below 55% concentration at temperatures under 10°C, limiting use to chilled applications above 5°C. Toxicity is low, as both components are non-flammable and environmentally benign (GWP=0 for ), though LiBr's corrosivity to and requires inhibitors like lithium chromate or molybdates. Operating temperatures span 20-100°C, ideal for or solar-driven systems, with a high circulation of 10-25, increasing solution pumping power but enabling effective absorption. Alternative pairs include ammonia with salts like lithium nitrate (NH₃-LiNO₃) for reduced circulation ratios (around 8-10) and organic fluids such as methanol-LiBr for mid-temperature ranges, though these are less common due to stability issues. Selection criteria prioritize the pair's range to match source and sink (e.g., 80-100°C for single-effect cycles), circulation ratio to balance pumping versus absorption efficiency, and rectification needs to prevent evaporator fouling. Environmental and factors, including and corrosivity, further guide choices, with non-toxic options preferred for indoor applications. Emerging research as of 2025 explores ionic liquids (ILs) as absorbents, paired with ammonia or water, to address limitations of traditional fluids. Examples include [EMIM][OAc] with ammonia, offering tunable solubility via NRTL models, low vapor pressure, and operation at 25-60°C without crystallization. ILs exhibit low toxicity, negligible flammability, and reduced corrosivity compared to LiBr, with environmental benefits from high thermal stability and recyclability, potentially improving COP by 20-30% in compact systems. Zeolite-based solid absorbents, such as 13X or SAPO-34 with water, are under investigation for hybrid absorption-adsorption cycles, providing high uptake (up to 0.3 kg/kg) at low pressures but requiring further scaling for refrigeration efficiency.
PropertyAmmonia-WaterLithium Bromide-WaterIonic Liquids (e.g., NH₃-[EMIM][OAc])
Operating PressureHigh (5-20 bar)Vacuum (0.01-0.1 bar)Moderate (1-10 bar)
Temperature Range-80 to 180°C20 to 100°C25 to 60°C
Circulation 2-1010-2510-15
ToxicityHigh ()LowLow
CorrosivityModerateHighLow
GWP000 (negligible)

System Configurations

Single-Effect Absorption Systems

The single-effect absorption refrigerator represents the simplest configuration of absorption cooling technology, featuring four primary components: a generator, absorber, condenser, and , interconnected to form a closed loop without mechanical compression. In this setup, the system utilizes a binary working fluid pair, such as as the and as the absorbent, to achieve through thermal energy input rather than electrical power. Operation begins with heat input to the generator, typically from low-temperature sources ranging from 80–100°C, which causes the vapor () to desorb or boil off from the strong absorbent solution, leaving a behind. The desorbed vapor then travels to the condenser, where it releases to the surroundings and liquefies, before expanding through the to absorb from the cooled space, producing the effect. Simultaneously, the from the generator flows back to the absorber via a and , where it reabsorbs the low-pressure vapor from the , forming a strong solution that completes the cycle; this absorption process is exothermic and requires cooling, often via ambient air or . Early commercial examples of single-effect absorption refrigerators include the gas-fired domestic models produced by Servel in the 1920s, which operated on the ammonia-water pair and were designed for quiet, electricity-free household cooling using natural gas or kerosene as the heat source. These units achieved a coefficient of performance (COP) typically in the range of 0.5–0.7, reflecting the efficiency of converting thermal input to cooling output under standard conditions. The primary limitation of single-effect systems stems from their reliance on a single desorption step in the generator, which constrains overall compared to more advanced configurations, as it does not recycle internal effectively for multiple refrigerant extractions.

Multi-Effect and Advanced Designs

Multi-effect absorption systems enhance by incorporating multiple stages of utilization, surpassing the limitations of single-effect configurations, which typically achieve a (COP) around 0.7. In double-effect systems, two generators operate in series: the vapor produced in the first generator serves as the source for the second, allowing for higher overall COP values of up to 1.2 while requiring elevated input temperatures between 150°C and 180°C. This design recovers that would otherwise be rejected, improving energy utilization in applications where high-temperature sources, such as waste from , are available. Building on double-effect principles, triple-effect systems further cascade heat recovery across three generators, achieving COPs as high as 1.8, which represents approximately a 30% improvement over double-effect chillers. These systems incorporate advanced features like generator-absorber heat exchange (GAX) cycles, where from the absorber is transferred to the generator to boost desorption , enabling even greater gains in low-grade recovery scenarios. Triple-effect configurations are particularly effective for utilizing mid-temperature sources, with studies showing COP enhancements of 25% to 65% compared to conventional multi-effect cycles through optimized internal recovery. Advanced designs extend these concepts to specialized configurations that address portability, sustainability, and compactness. Diffusion absorption refrigerators eliminate the need for mechanical pumps by employing an inert gas, such as hydrogen, as an auxiliary fluid alongside ammonia refrigerant and water absorbent; this setup relies on thermal diffusion and bubble pumping for circulation, enabling operation without electrical input and achieving COPs around 0.2-0.3 in compact units. Solar-assisted systems integrate flat-plate or evacuated-tube collectors to supply the necessary desorption heat, with prototypes demonstrating reliable cooling in off-grid environments by leveraging intermittent solar energy for generator heating. Hybrid systems combine absorption cycles with vapor-compression refrigeration, using absorption to precool or assist the compressor stage, which can reduce overall energy consumption by 20-30% in waste-heat-driven setups. In the 2020s, innovations in microchannel heat exchangers have enabled more compact absorption chillers, with membrane-based designs improving efficiency in absorbers and desorbers to support for residential or portable applications while maintaining comparable to larger units. These multi-effect and advanced systems find prominent use in large-scale chillers for commercial buildings and industrial facilities, where triple-effect units powered by provide with capacities exceeding 1 MW, contributing to energy savings of up to 40% over electric vapor-compression alternatives.

Applications

Domestic and Portable Uses

Absorption refrigerators have been widely adopted in recreational vehicles (RVs), campers, and boats since the mid-20th century, providing reliable off-grid cooling powered by gas or elements. Their development for mobile applications began in the 1950s, with early models like those produced by (now Dometic) in 1956 enabling independent operation without reliance on external electricity, which was ideal for remote travel and boating environments. This versatility allows users to maintain in varying conditions, such as during extended trips where is unavailable. In household settings, gas-powered absorption refrigerators serve remote areas, cabins, and hotels where stable is limited, offering capacities typically ranging from 100 to 300 liters to accommodate family needs or guest rooms. These units, often three-way models operable on , 12V DC, or 110V AC, ensure consistent cooling in off-grid homes or venues without the of compressor-based alternatives. For instance, models with around 265 liters are common for such installations, balancing space efficiency with practical storage. Portable variants of absorption refrigerators, including battery-assisted and solar-heated options, cater to and outdoor activities, with modern examples like Dometic's three-way units providing compact cooling for tents or tailgates. These portable models, often in 40- to 100-liter sizes, leverage solar thermal input for sustainable operation during extended stays in remote areas. Their quiet operation enhances user comfort in serene settings. As of 2025, the market for absorption refrigerators maintains niche but steady demand, driven by growing interest in energy-independent living, RVs, and off-grid lifestyles, valued at USD 1.76 billion in 2025 and projected to reach USD 3.49 billion by 2034 at a of 7.9%, supported by advancements in portable and solar-compatible designs.

Industrial and Commercial Applications

Absorption chillers play a pivotal role in (HVAC) systems for large commercial buildings such as hospitals, hotels, office complexes, and educational campuses, where they utilize from plants to produce chilled water for space cooling. These systems often employ lithium bromide-water pairs, which are particularly dominant in applications exceeding 100 tons of capacity, enabling efficient operation with heat sources like low-pressure or hot water from combined heat and power (CHP) setups. For instance, a 400-ton lithium bromide chiller integrated with three 600 kW reciprocating engines has been deployed at a facility to leverage exhaust heat for process and space cooling. In and chemical manufacturing plants, absorption refrigeration systems harness byproduct or hot to provide cooling for processes such as cold storage and equipment , reducing reliance on electricity-intensive vapor-compression alternatives. Ammonia-water absorption units, for example, deliver 160 tons of at 25°F for cold rooms in facilities, utilizing high-temperature sources effectively in environments with abundant generation. Similarly, systems support chemical plants by cooling process fluids, capitalizing on from reactions or boilers to maintain operational temperatures without additional energy inputs. District cooling networks represent a major commercial application, particularly in regions with high cooling demands and access to renewable or sources, such as and the . In , large-scale absorption chillers, including units up to 5,000 tons, power centralized systems like the Saitama Shinsothin west area facility, which integrates gas turbine for urban cooling distribution. projects, such as those in the UAE, incorporate absorption chillers with geothermal resources to supply chilled water across districts, as seen in the G2COOL plant using hot water from geothermal wells at over 90°C. These systems often combine solar thermal inputs, enhancing in arid climates with intense solar exposure. As of 2025, absorption refrigeration is increasingly adopted in data centers for sustainable cooling, recovering low-grade from servers to drive the absorption cycle and minimize grid electricity use. Innovations like compression-assisted absorption refrigeration-heating pumps enable year-round heat recovery in liquid-cooled data centers, adapting to varying climates and reducing operational carbon footprints. integrations further promote this trend, converting server exhaust heat into to support high-density computing demands. Multi-effect designs enhance scalability for these large installations by improving with staged heat utilization.

Performance and Considerations

Advantages

Absorption refrigerators feature few or no , typically limited to a small liquid pump in some designs, which contributes to their quiet operation and minimal . This absence of compressors and other mechanical components results in significantly reduced levels, making them suitable for noise-sensitive environments. The simplified mechanical structure also leads to lower maintenance requirements, as there are fewer components prone to wear and failure. Furthermore, these systems often exhibit long lifespans, typically lasting 10–15 years or more with proper care, due to their robust and low-stress design. A key strength of absorption refrigerators lies in their ability to utilize diverse heat sources, such as , , or , rather than relying primarily on . This flexibility allows them to operate with low-grade heat inputs, drastically reducing consumption and enabling applications in off-grid or remote locations where power availability is limited. By harnessing otherwise unused , these systems promote energy efficiency in settings with abundant heat resources. The vibration-resistant nature of absorption refrigerators, stemming from their lack of moving parts, enhances their reliability in challenging environments, such as marine vessels or recreational vehicles (RVs) subject to constant motion. This durability ensures consistent performance without degradation from shocks or tilts common in mobile applications. Economically, absorption refrigerators offer lower operating costs in scenarios with access to inexpensive or free heat sources, as the primary energy input is rather than electrical, leading to substantial savings over time and potential payback through reduced utility expenses.

Limitations and Efficiency

Absorption refrigerators exhibit lower coefficients of performance (COP) compared to vapor-compression systems, typically around 0.7 for single-effect and 1.2–1.4 for multi-effect designs, while vapor-compression refrigerators achieve COP values of 3 to 5 under similar conditions. This disparity necessitates significantly more heat input to achieve equivalent cooling output, as the absorption process relies on thermal energy rather than mechanical work, leading to reduced overall efficiency. Furthermore, efficiency in absorption systems declines under varying load conditions, such as fluctuating heat source temperatures or partial cooling demands, due to the inherent sensitivity of the absorption-desorption cycle to thermal stability. Ongoing research, including membrane-based and falling film absorbers, aims to improve efficiency and reduce size constraints as of 2025. The physical design of absorption refrigerators contributes to their bulkier size and greater weight relative to vapor-compression counterparts, primarily because of the large heat exchangers required for the generator, absorber, and condenser components. These dimensions limit their portability and suitability for space-constrained applications, often requiring a significantly larger installation area in industrial setups. Working fluids in absorption systems introduce specific safety and operational challenges. , commonly paired with , is both toxic and flammable, posing risks of hazards, , and in the event of leaks, which necessitates robust , ventilation, and monitoring measures in enclosed environments. Similarly, lithium bromide solutions, used in water-lithium bromide pairs, are prone to when water content drops below critical levels—often during low loads or high generator temperatures—potentially blocking flow paths and requiring manual or automated de-crystallization procedures to restore operation. Environmentally, while absorption refrigerators employ low (GWP) fluids like water or —resulting in near-zero direct emissions—their higher offsets some benefits by increasing indirect from heat sources. However, evolving regulations, such as the 2025 EPA phasedown of high-GWP hydrofluorocarbons under the AIM Act, position absorption systems favorably for in heat-recovery applications, where utilization can mitigate overall energy demands.

References

  1. https://www.sciencedirect.com/topics/engineering/absorption-refrigeration
  2. https://www.cedengineering.com/userfiles/M04-025%20-%20Overview%20of%20Vapor%20Absorption%20Cooling%20System%20-%20US.pdf
  3. https://www.energy.gov/sites/prod/files/2013/11/f4/absorption_future.pdf
  4. https://invention.si.edu/invention-stories/einstein-szilard-refrigerator
  5. https://ucanr.edu/sites/default/files/2017-11/274428.pdf
  6. https://www.sciencedirect.com/science/article/pii/S1364032113001834
  7. https://www.sciencedirect.com/science/article/pii/S0140700715003011
  8. https://doi.org/10.1016/j.aej.2020.01.036
  9. https://www.epa.gov/sites/default/files/2018-05/documents/listofkeymeasurements.pdf
  10. https://physics.info/refrigerators/
  11. https://www.dmg-lib.org/dmglib/handler?biogr=24511004
  12. https://www.researchgate.net/publication/256454761_MAKING_SCIENCE_COOLER_CARRE%27S_APPARATUS
  13. https://www.ashrae.org/about/mission-and-vision/ashrae-industry-history/air-conditioning-and-refrigeration-timeline
  14. https://archive.org/stream/recollectionsofp00rimm/recollectionsofp00rimm_djvu.txt
  15. https://patents.google.com/patent/US1781541A/en
  16. https://www.researchgate.net/publication/383427059_Einstein%27s_Contribution_to_Refrigeration_The_Einstein-Szilard_Refrigerator_and_Advancements_in_Gas_Absorption_Cooling
  17. https://refresearch.com/the-first-absorption-refrigerator/
  18. https://evolutionhomeappliances.weebly.com/refrigerators-1927-1950s-gas.html
  19. https://www.warehouseappliance.com/blog/all-about-the-servel-gas-refrigerators/
  20. https://www.dometicgroup.com/en-us/our-company/history
  21. https://familyrvingmag.com/2005/05/01/dometic-corporation-making-life-easier/
  22. https://www.gulfstreamcoach.com/rvrefrigerationbasics
  23. https://www.epj-conferences.org/articles/epjconf/abs/2025/11/epjconf_cofmer2025_04002/epjconf_cofmer2025_04002.html
  24. https://www.sciencedirect.com/science/article/abs/pii/S1359431125010324
  25. https://pmc.ncbi.nlm.nih.gov/articles/PMC12232040/
  26. https://ideas.repec.org/a/eee/energy/v338y2025ics0360544225042896.html
  27. https://www.intechopen.com/chapters/1132388
  28. https://fiveable.me/thermodynamics-ii/unit-6/absorption-refrigeration-systems/study-guide/cOeoF8teXt04Vb89
  29. https://www.jestr.org/downloads/Volume6Issue5/fulltext18652013.pdf
  30. https://www.mdpi.com/1996-1073/16/9/3610
  31. https://www.osti.gov/servlets/purl/1783056
  32. https://www.researchgate.net/publication/254409797_A_review_of_working_fluids_of_absorption_cycles
  33. https://pubs.acs.org/doi/10.1021/acs.chas.2c00041
  34. https://repository.gatech.edu/bitstreams/21456281-d139-4235-87ce-ddc1d2c943d8/download
  35. https://www.sciencedirect.com/topics/engineering/lithium-bromide-absorption-cycle
  36. https://iopscience.iop.org/article/10.1088/1757-899X/376/1/012007/pdf
  37. https://www.sciencedirect.com/science/article/abs/pii/S0196890420308049
  38. https://journals.sagepub.com/doi/10.1155/2013/620592
  39. https://www.sciencedirect.com/science/article/pii/S2772416625000294
  40. https://www.sciencedirect.com/topics/engineering/effect-absorption-refrigeration-cycle
  41. https://betterbuildingssolutioncenter.energy.gov/sites/default/files/attachments/CHP_Absorption_Chillers.pdf
  42. https://www.osti.gov/servlets/purl/78717
  43. https://www.sciencedirect.com/topics/engineering/double-effect-absorption-cooling-system
  44. https://academic.oup.com/ce/article/8/1/55/7512602
  45. https://www.thermaxglobal.com/tripple-effect-chiller/
  46. https://pubs.aip.org/aip/acp/article-pdf/doi/10.1063/5.0149485/18159535/140001_1_5.0149485.pdf
  47. https://journals.sagepub.com/doi/abs/10.1177/09544089231221762
  48. https://www.sciencedirect.com/science/article/abs/pii/S1359431102000492
  49. https://www.sciencedirect.com/science/article/pii/S0960148124007869
  50. https://ui.adsabs.harvard.edu/abs/2013ApEn..106..383H/abstract
  51. https://www.sciencedirect.com/science/article/abs/pii/S014070071830063X
  52. https://www.smadappliances.com/blogs/blog/absorption-fridge-versatile-cooling-for-rvs-hotels-and-camping
  53. https://www.vitrifrigo.com/en_en/products/outdoor/frigoriferi-a-gas-trivalenti
  54. https://www.alibaba.com/showroom/lpg-gas-kerosene-refrigerator.html
  55. https://www.smadappliances.com/blogs/product-blog/compressor-vs-absorption-refrigerators-a-comprehensive-comparison-and-selection-guide
  56. https://www.researchandmarkets.com/reports/6088231/absorption-refrigerator-market-size-share
  57. https://www.energy.gov/sites/prod/files/2017/06/f35/CHP-Absorption%20Chiller-compliant.pdf
  58. https://industrial.hitachiaircon.com/en/projects/district-heating-cooling/saitama
  59. https://www.linkedin.com/posts/michael-barnard-42446_underground-heat-urban-cool-the-physics-activity-7382488727840878592-6a46
  60. https://www.alfalaval.us/industries/hvac/district-cooling/
  61. https://www.sciencedirect.com/science/article/abs/pii/S0360544225042896
  62. https://xendee.com/insights/how-absorption-chillers-boost-microgrid-performance
  63. https://www.irjet.net/archives/V4/i1/IRJET-V4I147.pdf
  64. https://ui.adsabs.harvard.edu/abs/1993umd..rept.....H/abstract
  65. https://www.thevanconversion.com/post/these-are-the-best-fridges-for-campervan
  66. https://rvserviceclub.com/blog/rv-refrigerator-not-cooling/
  67. https://courses.ems.psu.edu/eme811/node/670
  68. https://jsee.uctm.edu/index.php/see/article/download/135/134/134
  69. https://www.sciencedirect.com/science/article/pii/S1110016820300375
  70. https://coolingbestpractices.com/technology/chillers/busting-four-myths-about-absorption-cooling
  71. https://www.cibsejournal.com/cpd/modules/2009-11/
  72. https://www.physicsforums.com/threads/when-the-cop-of-refrigerator-is-greater-or-less-than-1.950829/
  73. https://www.cibse.org/media/e3kbrabr/datasheet-7-absorption-cooling.pdf
  74. https://www.sciencedirect.com/science/article/abs/pii/S1226086X25006380
  75. https://apps.dtic.mil/sti/tr/pdf/ADA325700.pdf
  76. https://www.epa.gov/sites/default/files/2013-11/documents/ammonia.pdf
  77. https://www.vamtec.com/crystallisation/
  78. https://docs.johnsoncontrols.com/chillers/api/khub/documents/Id9EzqSM6VixEr4_VsD9bg/content
  79. https://www.epa.gov/system/files/documents/2025-09/ttrr-prepublication-version.pdf
  80. https://www.selecthomewarranty.com/blog/new-refrigerant-changes/
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