What are absorption chillers?
Absorption chillers use the counterintuitive practice of employing a heat source to provide the energy that drives cooling. In other words, it employs waste heat to deliver cooling or refrigeration.
The history of absorption chillers
After developing his revolutionary Theory of Relativity, Albert Einstein continued to practice science – arguably on a more humble level – by contributing to the invention of an absorption refrigerator in 1926 with his former student, Leo Szilárd.
However, the principles of absorption cooling were known well before this. Exploration of the absorption cycle began in 1700s when it was found that ice could be produced by evaporating pure water from a vessel contained within an evacuated container in the presence of sulphuric acid.
In 1810, it was discovered that ice could be produced from water in a pair of vessels connected together in the presence of sulphuric acid. But it was not until 1850 that French engineer Edmond Carré developed the first absorption machine using water and sulphuric acid.
Nine years later, his brother, Ferdinand, demonstrated an ammonia/water refrigeration machine and in 1860 Ferdinand received the first US patent for a commercial absorption unit.
Then, in 1950, a new system was introduced with water and lithium-bromide paired as working fluids for commercial purposes.
Absorption chillers today
Absorption refrigeration has come a long way since then. The latest technology includes pioneering Klima-Therm supplied chillers from World Energy which use ground-breaking technology to harness waste heat from industrial processes and buildings and convert it into chilled water for process or comfort cooling.
Lauded as the most efficient brand on the market, World Energy chillers are the most effective solution for turning waste heat into usable free cooling, including combined heat, power, and cooling trigeneration schemes. They are also widely used in heat network/district heating applications.
Absorption refrigeration systems are a particularly efficient and environmentally friendly option for various applications because they can use waste heat from industrial processes and buildings, converting it into chilled water for cooling purposes.
How do absorption chillers work?
So how does absorption refrigeration work? In fact, its operation is relatively simple in principle. There are, essentially, two fluids employed in an absorption chiller – the absorbent and the low boiling point refrigerant. Heat transfer occurs when the refrigerant is absorbed by the absorbent.
The absorption cooling cycle depends upon three fundamental scientific principles:
- A liquid will boil (or vaporise to become a gas) when heated and a gas will condense when cooled.
- When the pressure above a liquid is reduced, the vapour pressure needed to encourage boiling is also reduced and the boiling point of the liquid decreases.
- Heat naturally flows from warmer to cooler surfaces.
Using these principles, An absorption chiller is a closed loop cycle that employs waste heat to provide cooling or refrigeration. Absorption cooling occurs in three phases – evaporation, absorption, and regeneration. This results in mechanical circulation of the liquid without the need for a pump.
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Absorption chillers and CCHP systems
Absorption chillers are commonly used in combined cooling, heating, and power (CCHP) systems. Rather than using mechanical rotating devices to compress the refrigerant vapour they employ heat so they can be driven by the steam, hot water or high temperature exhaust gas. This results in electricity needed for the conventional refrigeration being dramatically reduced, and the noise of the cooling process lowered significantly.
The sequence in the absorption refrigeration cycle is in three steps:
- Evaporation – Liquid refrigerant evaporates extracting heat from its surroundings.
- Absorption -The second fluid, in a depleted state, sucks out the now gaseous refrigerant, producing a refrigerant-saturated liquid which then flows to the next step.
- Regeneration – The refrigerant-saturated liquid is heated, making the refrigerant evaporate.
Absorption refrigeration offers a host of benefits, including:
- Efficiency – this technology consumes less electrical power than, say, vapour compression systems, because its input energy is based on low grade heat from waste in, for example, power plants and factories, or from renewables such as biomass, solar and geothermal sources.
- Environmental friendliness – Absorption refrigeration poses no threat to the ozone level and has less impact on global warming than most other options. It also enables the use of low global warming potential refrigerants. Since absorption refrigeration can be driven by low-grade heat and renewable sources, it reduces CO2 emissions.
- Clean operation – There is no need to use refrigerant lubricants.
- Cost effectiveness -Fuel costs are lower than the electrical power costs because heat to drive the cooling process can be generated by a number of sources including direct gas and oil firing, gas turbine exhausts, hot process fluids, and heat recovery from steam and flue gases.
- Welfare – Absorption refrigeration generates less noise and vibration than alternative systems, leading to better comfort levels and greater wellbeing.
- Enhanced maintenance – Fewer moving parts leads to reduced wear and tear and therefore less demand for servicing and maintenance.
