Absorption Chillers: An Environment-friendly Alternative to Traditional Cooling Systems

Absorption Chillers: An Environment-friendly Alternative to Traditional Cooling Systems

How Absorption Chillers Work

In an absorption chiller, a refrigerant such as lithium bromide is absorbed and desorbed by a heat exchange fluid like water to produce chilled water or another coolant. During the absorption process, the refrigerant vapor is drawn into a heat exchanger coil bathed in a hot water/steam solution where it condenses releasing its latent heat of condensation. The condensed refrigerant is then absorbed by the strong solution of lithium bromide and water.

Simultaneously, a weak solution of refrigerant and water is circulated to a generator where it is heated using a natural gas, propane, or waste heat source. This causes the refrigerant in the weak solution to evaporate out, concentrating the strong solution. The pure gaseous refrigerant rises and passes through a condenser releasing its heat of vaporization. The now liquid refrigerant travels through an expansion valve where it undergoes adiabatic flash evaporation cooling its temperature significantly before entering the evaporator core. Here it absorbs heat from the chilled water or cold liquid circuit evaporating once more before restarting the cycle.

Types of Absorption Chillers

There are three main types of sorption based on the refrigerant/absorbent pair used -

1. Lithium bromide/water - These are the most common and can produce chilled water in the range of 40-60°F. They require hot water at 150-210°F or steam at 200-230°F as the driving heat source.

2. Ammonia/water - They produce lower temperature chilled water around 23-40°F and operate on lower temperature waste heat in the 130-180°F range. However, ammonia is toxic and flammable.

3. Hydrogen/water - Rarer than the other two types, they can generate very low temperatures below 23°F using higher temperature waste heat of 200-270°F. But hydrogen is also flammable and poses safety risks.

Applications

With cooling capacities ranging from 100 tons to multiple megatons, sorption can serve a variety applications from small commercial buildings to large districts energy plants and industrial facilities. Some common applications include -

- Large hospitals and medical facilities - Their continuous cooling needs can utilize waste heat from cogeneration plants.

- District cooling systems - Cities are increasingly using Absorption Chiller to take advantage of plentiful waste heat and reduce primary energy usage.

- Hotels and resorts - Their substantial cooling loads, especially in hot climates, are well-suited for sorption paired with onsite CHP systems.

- Food processing plants - Waste heat from boilers and dryers can drive sorption for refrigeration needs.

- Printing presses - Their thermal output is effectively used in multi-effect sorption for air conditioning.

- Greenhouses - Waste energy from biomass combustion offers potential for sustainable cooling of commercial greenhouses.

Benefits Over Conventional Chillers

The primary advantage of sorption over electric driven vapor compression chillers is their ability to leverage lower grade waste heat or fuel sources rather than relying solely on electricity. Some other major benefits include:

- Significantly reduced operating costs - Cooling production is decoupled from grid electricity usage, lowering energy bills substantially.

- Enhanced sustainability profile - Their utilization of renewable and recoverable heat for cooling lowers primary fossil fuel dependency and emissions.

- Increased resiliency - The cooling system can keep functioning even if electricity goes down as long as the thermal energy source remains available.

- Lower maintenance needs - No compressors or moving fluid parts implies fewer repairs and component replacements over time.

- Tax incentives - Many governments offer capital grants and tax credits for installing sorption as part of sustainable building designs.

Challenges

While sorption outperform traditional chillers in certain applications, they also impose some challenges compared to their electric counterparts -

- Higher initial capital costs - First costs for equipment, installation and thermal distribution piping are generally higher than vapor compression units.

- Lower efficiencies - Cooling coefficient of performance (COP) typically ranges between 0.6-1.2 versus 2.5-5.0 for modern centrifugal compressors.

- Complex systems - Multiple thermal loops and specialized working fluids require more planning, engineering and commissioning expertise.

- Lower thermal efficiency at part loads - Performance degrades significantly when cooling demands decrease below full capacity.

- Limited hot water/steam sources - Suitability depends on availability of matching grade waste heat nearby. Transporting this medium increases costs.

By leveraging recoverable thermal energy from renewable or cogeneration sources, sorption deliver significant economic and environmental advantages over electric chillers. Though capital intensive, their lower operating expenses and higher sustainability make them a very attractive long term alternative for many large scale cooling applications. With proper optimization and control strategies, absorption systems promise to enhance building efficiency and reduce carbon footprint of cooling sector.
 
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About Author:
Ravina Pandya, Content Writer, has a strong foothold in the market research industry. She specializes in writing well-researched articles from different industries, including food and beverages, information and technology, healthcare, chemical and materials, etc. (https://www.linkedin.com/in/ravina-pandya-1a3984191)