Absorption chillers: what they are, how they work, advantages, and industrial applications
In industrial processes that generate large amounts of waste heat—from cogeneration to materials processing, and even exhaust flue gases from a production plant—transforming that heat into useful cooling energy is one of the most concrete energy efficiency strategies available to companies.
This is exactly the task of absorption chillers: refrigeration machines that, instead of consuming electricity like traditional compression chiller units, operate thanks to a thermal source.
In this guide, we analyze in detail what they are, how they work, what advantages they offer, and in which sectors absorption chiller units are employed, with a direct comparison to compression chillers and some practical indications on maintenance.
Table of Contents
- What is an absorption chiller
- The potential of industrial waste heat
- How an absorption chiller works
- The advantages of absorption systems
- Applications of absorbers
- Absorption chillers vs. compression chillers: a direct comparison
- Maintenance of absorption plants
- Frequently asked questions about absorption chillers
What is an absorption chiller
An absorption chiller is a refrigeration machine capable of producing chilled water using thermal energy instead of electrical energy as the main power source.
Instead of the mechanical compressor—the heart of traditional chillers—an absorber utilizes a thermodynamic cycle based on the chemical affinity between two substances: a refrigerant fluid (usually water) and an absorbent solution (in the most common configuration, lithium bromide).
For this reason, in the technical language of the industrial HVAC sector, absorption chillers are also called:
- absorbers
- absorption chiller units
- lithium bromide absorbers (when they use this specific saline solution)
- absorption refrigerators
The physical principle behind this technology is not new: the absorption refrigeration cycle was observed experimentally as early as the first half of the nineteenth century and developed industrially a few decades later, even before the spread of electromechanical compressors.
Today, in a context of energy transition and recovery of thermal waste, this technology is experiencing a new centrality.
The key difference: thermal energy instead of electricity
While a compression chiller transforms electrical energy into cooling energy via a compressor, an absorber uses heat as the primary input—hot water, steam, exhaust gases, or direct gas flame—requiring electricity only for the operation of circulation pumps and auxiliary systems, with electrical consumption reduced by approximately 90% compared to an equivalent electric chiller.
The potential of industrial waste heat
The industrial sector is responsible for approximately 25% of final energy consumption and over 50% of CO₂ emissions at the European level. Globally, industry accounts for about one-third of total energy consumption, and wastes nearly half of it in the form of unused heat flows (ENEA, Integrated Energy Solutions Laboratory, 2020).
Regarding Italy specifically, the ENEA study conducted in collaboration with the Universities of Rome Tor Vergata, L'Aquila, and Udine estimates that the available industrial waste heat is approximately 26 TWh/year (GSE data, 2016). A value that places our country in an intermediate position compared to other major European countries: well below France (100 TWh/year) and Germany (87.8 TWh/year), but higher than markets such as Austria, the United Kingdom, and Norway.
Confirming the centrality of the issue also at the continental level, the EHPA (European Heat Pump Association) reports that in Europe over 60% of industrial consumption is destined for heat production, largely still from fossil sources, a fact that makes it clear how much the recovery of this heat represents today one of the most concrete energy efficiency levers available to Italian companies.
Within the scope of the same study, ENEA built a database of over 200 real cases of industrial heat recovery at low and very low temperatures, obtained also from the analysis of over 500 energy audits sent by large companies and energy-intensive companies pursuant to Legislative Decree. 102/2014. The sectors that emerged as most promising for recovery are food (in particular dairy and bakery products) and textiles; among the recovery technologies already commercialized in their respective power fields, the study explicitly cites ORC plants, heat pumps, and absorption refrigeration machines.
A useful fact to correctly frame the issue: according to the conclusions of the ENEA study, the barriers that today hinder the spread of these interventions are not technological, but organizational, informational, communicative, and financial; an aspect that makes it even more strategic to rely, right from the design phase, on a partner with consolidated technical expertise in recovery systems.
The Italian regulatory framework: cogeneration, trigeneration, and GSE incentives
In Italy, trigeneration plants that integrate an absorber for the production of cooling energy from recovered heat can fall under the discipline of High-Efficiency Cogeneration (HEC), regulated by Legislative Decree 20/2007 (transposition of the European directive on cogeneration) and managed by the GSE (Energy Services Manager).
A plant is recognized as HEC when the primary energy saving (PES) is at least 10% for units with power greater than 1 MWe, or simply positive for micro-cogeneration (under 50 kWe) and small-scale cogeneration (under 1 MWe).
HEC-qualified plants can access White Certificates (TEE), tradable titles that remunerate the energy savings achieved.
In the first half of 2025 alone, the GSE initiated 2,482 procedures for HEC recognition, with over 1,079,000 TEEs issued or withdrawn, a sign of the growing spread of these plants in Italy as well.
How an absorption chiller works
The cycle of a lithium bromide absorber develops through four main components, which work in a continuous sequence.
- Generator
This is where the heat that powers the cycle enters. The solution of water and lithium bromide is heated until the water reaches boiling point. The water vapor that forms is separated from the lithium bromide, which remains concentrated and ready to be recirculated.
- Condenser
The water vapor coming from the generator is cooled and condensed thanks to cooling water, typically coming from an evaporative tower. The result is water in a liquid state, ready for the next phase.
- Evaporator
The condensed water is evaporated under high vacuum conditions at very low temperatures (around 4°C). By evaporating, it removes heat from the plant water to be cooled, which typically enters at about 14°C and exits at about 7°C: this is the chilled water that will then be used for space cooling or production processes.
- Absorber
The low-temperature water vapor generated in the evaporator is absorbed by the concentrated lithium bromide solution, which has a strong hygroscopic affinity with water. This absorption generates heat, which is transferred to the cooling circuit and disposed of, for example, via an evaporative tower.
At this point, the solution, now diluted, is pumped back into the generator, where the cycle begins again.
Single and double-effect absorbers
There are two main configurations:
- Single-effect absorbers: a single generator, powered by hot water at relatively low temperatures (70-100°C). They are the ideal solution for low-temperature waste heat recovery or for solar cooling.
- Double-effect absorbers: feature two generators in thermal cascade, require higher temperature heat sources (up to 160°C) but achieve higher coefficients of performance (COP), up to about 1.4.
The advantages of absorption systems
Compared with traditional electric chillers, absorption chiller units offer a series of advantages that make them particularly interesting for the industrial sector.
- Negligible electrical consumption: the only moving parts are the circulation pumps for the solution and the refrigerant; since there is no electric compressor, the electricity requirement is drastically reduced.
- Waste heat recovery: they can be powered by thermal waste from cogenerators, industrial furnaces, gas turbines, production processes, or solar panels, transforming a lost energy cost into useful cooling energy.
- No impact on the ozone layer: they do not use synthetic refrigerants based on chlorofluorocarbons (CFCs) or HFCs with high global warming potential, but water as the primary refrigerant fluid.
- Quiet and vibration-free operation: the absence of a mechanical compressor drastically reduces noise and vibrations compared to a compression chiller.
- Reliability and long life: the reduced presence of moving mechanical components translates into less wear and less need for corrective interventions over time.
- Suitable for trigeneration (CCHP): they integrate naturally into cogeneration plants, allowing for the production of electricity, heat for winter heating, and cold for summer cooling from the same primary energy source.
Applications of absorption chillers
Thanks to the ability to exploit different thermal sources, absorbers find use in a wide range of industrial and commercial contexts.
- Trigeneration (CCHP): combined with a cogenerator, they allow for summer air conditioning starting from heat recovered from exhaust gases or engine cooling water.
- Process heat recovery: in sectors such as plastics processing, the food industry, steel, or chemicals, where large amounts of residual heat are normally dispersed into the atmosphere.
- Solar cooling: coupled with solar thermal collectors, they produce summer cooling by exploiting solar energy, precisely during the period of the year when the availability of heat from the sun is at its maximum.
- District heating and heat networks: integrated into district heating plants to also provide a district cooling service in the summer months.
- Large-scale industrial environments: warehouses, logistics hubs, railway workshops, hangars, and sports facilities, where summer cooling is often accompanied by radiant heating systems in the winter season.
- Data centers and facilities with continuous thermal loads: where reliability and the possibility of recovering waste heat represent a significant economic and energy advantage. (More information on this highly topical subject at the following links: https://www.enertechsolution.it/recupero-di-calore-e-raffreddamento-nei-data-center/ and https://www.edilportale.com/news/2025/07/focus/recupero-calore-da-data-center-per-teleriscaldamento-urbano_106309_67.html)
Absorption chillers vs. compression chillers: a direct comparison
Understanding the differences between the two technologies is fundamental for choosing the most suitable solution for your production context.
|
Feature |
Absorption chillers |
Compression chiller |
|---|---|---|
|
Primary energy source |
Thermal energy (hot water, steam, flue gases, gas) |
Electrical energy |
|
Electrical consumption |
Very low (only auxiliary pumps) |
High |
|
Refrigerant |
Water (with lithium bromide as absorbent) |
Synthetic refrigerant gases (HFC, HFO) |
|
Moving components |
Very few (only pumps) |
High-speed compressor |
|
Noise and vibrations |
Very limited |
Higher |
|
Impact on the ozone layer |
None |
Depends on the refrigerant used |
|
Ideal for |
Waste heat recovery, cogeneration, solar cooling |
Contexts without availability of residual heat |
|
Footprint and weight |
Generally greater |
More compact |
|
Initial investment |
Higher |
Generally lower |
|
Operating costs |
Low if powered by recovery heat |
Linked to the cost of electrical energy |
In summary: the compression chiller remains the simplest and most economical choice in the absence of recoverable heat sources. The absorption chiller, on the other hand, becomes extremely convenient wherever waste heat is already available, transforming a lost energy cost into a competitive advantage, with a return on investment that is faster the higher the value of the recovered heat.
Maintenance of absorption plants
To guarantee efficiency and durability over time, a lithium bromide absorber requires a specific scheduled maintenance plan, different from that of a traditional compression chiller.
Predictive maintenance: data collection and artificial intelligence
The absorber can be connected to the Internet via a remote monitoring system, which collects the main operating parameters of the plant in real time (temperatures, pressures, vacuum level, solution concentration, flow rates) and makes them available through a dashboard that can be consulted by those who manage or service the plant.
The collected data is processed, also with the aid of artificial intelligence algorithms, to identify ongoing anomalies or deviations that may anticipate a failure.
This approach, known as predictive maintenance, allows the operator to:
- intervene before an anomaly turns into a plant shutdown;
- understand precisely where and how to intervene, reducing diagnostic times;
- establish the level of urgency for each intervention, prioritizing real criticalities.
The result is a maintenance plan built on actual plant data, rather than on fixed intervals established a priori: an approach that reduces machine downtime and, consequently, also the costs related to service interventions.
Scheduled maintenance interventions
- Vacuum control and purge system: the correct operation of the evaporator depends on maintaining very high vacuum conditions; a purge system removes non-condensable gases that accumulate over time and would compromise performance.
- Crystallization prevention: the lithium bromide solution, if excessively concentrated or cooled, can crystallize inside the circuits; modern control systems constantly monitor this risk.
- Corrosion inhibitors: lithium bromide has corrosive properties towards some metals; the solution is therefore treated with specific inhibitors, the level of which must be checked periodically.
- Cooling water treatment: the quality of the water in the evaporative tower directly affects the performance of the condenser and the absorber; a scale-prevention and antibacterial treatment plan (e.g., legionella control) is therefore necessary.
- Periodic COP verification: a drop in the coefficient of performance is often the first sign of a problem (insufficient vacuum, incorrect solution concentration, fouling of the heat exchangers) and must be monitored continuously.
- Professional scheduled maintenance: due to the chemical and thermodynamic nature of the cycle, maintenance interventions on an absorber require specialized personnel with specific skills in lithium bromide technology.
A well-structured maintenance plan not only extends the useful life of the plant but also allows for the maintenance over time of the energy efficiency advantages that make this technology convenient.
Frequently asked questions about absorption chillers
It is an absorption chiller that uses a solution of water and lithium bromide as the working fluid: water acts as the refrigerant, lithium bromide as the absorbent substance, allowing for the production of chilled water starting from a heat source instead of electrical energy.
Electrical consumption is reduced by approximately 90% compared to an equivalent compression chiller, as electrical energy is only needed to power circulation pumps and auxiliary systems, not for a compressor.
Yes. There are "small size" units designed for micro-cogeneration and solar cooling applications, in addition to high-power solutions for extensive industrial applications.
Single-effect absorbers use lower temperature heat (70-100°C) and are ideal for waste heat recovery; double-effect ones require hotter thermal sources (up to 160°C) but achieve higher efficiencies, with COPs up to about 1.4.
They require a different type of maintenance, focused on vacuum control, prevention of solution crystallization, and cooling water treatment, rather than on mechanical components.
Conclusion
In summary, absorption chillers represent today one of the most concrete solutions for reconciling energy efficiency, reduction of electrical consumption, and environmental sustainability in large-scale industrial and commercial contexts.
Whether it is recovering waste heat from a production process, integrating a trigeneration plant, or exploiting solar energy for summer cooling, lithium bromide absorbers offer an advantage that traditional compression chillers cannot replicate: transforming a lost energy cost into a resource.
A reliable technology that, with the right design and maintenance, represents one of the most effective levers for industrial decarbonization.
Carlieuklima, a company specialized in radiant heating solutions and evaporative cooling for medium and large-scale industrial, commercial, and sports environments, also deals with lithium bromide absorption chiller units. To learn more about the Euchill range of absorbers and evaluate the most suitable solution for your plant, contact our sales team, who will be able to provide all the information and documentation you need.
Euchill lithium bromide absorption chillers
Lithium bromide absorbers represent a sustainable, high-efficiency solution for chilled water production in the industrial sector and space climatization. They transform thermal energy into cooling energy, reducing consumption and emissions.
Sources/Bibliography
- ENEA — Miriam Benedetti, Lorena Giordano, Alessandra Gugliandolo (Integrated Energy Solutions Laboratory) — Solutions for low-temperature heat recovery in industry, Energy, Environment and Innovation, 3/2020, DOI 10.12910/EAI2020-084: eai.enea.it
- GSE — Energy Services Manager — Evaluation of the national and regional potential for the application of high-efficiency cogeneration and efficient district heating, 2016 (source of the data on 26 TWh/year of available waste heat in Italy, cited in ENEA 2020)
- QualEnergia.it — Industrial energy efficiency: keep an eye on thermal consumption and heat recovery (EHPA data: over 60% of European industrial consumption destined for heat production): qualenergia.it
- Cornell University, eCommons — Absorption Chilling: Part 1 (COP values for single, double, and triple-effect cycles): ecommons.cornell.edu
- U.S. Department of Energy — Combined Heat and Power Technology Fact Sheet Series: Absorption Chillers (COP data): energy.gov/eere/amo/articles/absorption-chillers-chp-systems-doe-chp-technology-fact-sheet-series-fact-sheet
- GSE — Energy Services Manager — High-Efficiency Cogeneration: gse.it/servizi-per-te/efficienza-energetica/cogenerazione-ad-alto-rendimento
- Legislation — Legislative Decree February 8, 2007, n. 20 (transposition of Directive 2004/8/EC on high-efficiency cogeneration): normattiva.it
