Absorption chillers work on the principle of absorption refrigeration where a refrigerant is absorbed into a liquid and when this liquid evaporates, it extracts heat from the surrounding environment, thereby providing cooling. In it, the refrigerant is water and the absorbent is a lithium bromide solution. When water is absorbed into the lithium bromide solution it becomes a concentrated solution and heat is released which can be used to drive the process. This process allows it to utilize waste heat to provide cooling, making them more environment friendly than conventional electric chillers.
Working Process
The basic components of it are an absorber, generator, condenser and evaporator. In the generator, a heat source such as natural gas, district heating or industrial waste heat is used to evaporate water from the lithium bromide solution, concentrating it. The water vapor travels to the condenser where it condenses into liquid water. This liquid water moves to the evaporator where it absorbs heat from the surroundings and evaporates. The water vapor is then absorbed by the lithium bromide solution in the absorber. When the solution absorbs water vapor, it becomes dilute again and releases heat which is dissipated using cooling towers or fluid coolers. The diluted solution is then pumped back to the generator to continue the cycle.
Types
There are mainly two types of it based on the type of absorbent used -
1. Lithium Bromide: As discussed above, these use lithium bromide as an absorbent and water as the refrigerant. They have a maximum operating temperature of 170°C making them suitable for waste heat sources like steam or hot water below this temperature.
2. Ammonia-Water: These use an ammonia-water mixture instead where ammonia acts as the refrigerant and water as the absorbent. They can utilize higher temperature heat sources up to 230°C making them suitable where higher temperature steam is available. However, they are more capital intensive than lithium bromide units.
Applications
Some key applications where absorption chillers are commonly used are:
- Hotels, Hospitals and Large Buildings: They utilize waste heat from cogeneration plants, boilers or chillers to provide space cooling with minimal electricity usage.
- Industrial Facilities: Process orco-generationplants in industries like refineries, pulp & paper mills generate high temperature steam which can directly run absorption chillers.
- District Heating Systems: Excess heat from district cogeneration plants is used to power Absorption Chillers integrated with the district cooling network.
- Renewable Energy Plants: Geothermal, solar thermal and biomass plants produce waste heat that can activate absorption chillers for heating and cooling.
Advantages
The main advantages of it over traditional electric chillers include:
- Lower Operational Cost: They utilize cheap waste heat and eliminate electricity usage of compressor, reducing energy and maintenance costs.
- Carbon Footprint Reduction: By using waste heat, they lower primary energy consumption from the grid, helping organizations meet carbon reduction targets.
- Reliability: Without any moving parts like compressors, it have a lifespan over 25-30 years and require minimal maintenance.
- Grid Load Management: They allow shifting of cooling loads away from peak grid usage since waste heat can operate chillers round the clock.
- Leverage Renewables: Heat from solar, biomass, geothermal plants can be valorized for cooling via it.
Market Growth and Future of Absorption Cooling
Its demand is increasing across green buildings, hospitals and industrial processes requiring large scale cooling. Trane, Yazaki, Broad Air Conditioning, Johnson Controls, Carrier Corporation etc are major manufacturers of absorption chillers. The technology would play a key role in decarbonization of cooling as renewable and waste heat based solutions gain more prominence worldwide. Overall, it provide a viable alternative to traditional electric chillers from economic and environmental perspectives.
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