What’s the difference between absorption and adsorption chillers?
The main difference between adsorption chillers and absorption chillers is during the adsorption method the water is adsorbed onto a solid (the non-hazardous or corrosive silica gel) and in the absorption method the water is dissolved into a liquid (the corrosive lithium bromide).
Both styles use evaporation, absorption, and condensation to chill water which can be utilised in refrigeration or cooling systems.
An adsorption chiller uses water as the refrigerant (no fluorocarbons) and silica gel as the adsorption material.
Adsorption chillers can effectively utilise the waste heat from power generation which can be used for energy efficient refrigeration, eg milk cooling requirements on dairy farms. Solar heat or waste heat is ideal for adsorption chillers as they work effectively using an inlet hot water of around 65℃ to 100℃.
Offering an extremely energy-efficient operation, adsorption chillers utilise a system where water passes through an evaporator, two adsorption heat exchangers, and condenser cycle. This cooling cycle is driven by the evaporation and condensation of the water rather than electricity. The small amount of power used by the unit is utilised by the pump.
The silica gel lowers the humidity inside the unit which assists the evaporation of water at a lower temperature. This process is further helped by keeping the atmospheric pressure inside the adsorption chiller low to further reduce the evaporation point of the water.
Benefits of adsorption chillers
- Energy-efficient - use less than 1kW.
- Minimal running costs.
- Long life - last around 30 years.
- Uses water as a refrigerant rather than potentially environmentally harmful fluorocarbons and gases.
- Easy to use and maintain.
- Work well in cooler climates.
- Allow for continuous operation.
- Minimal maintenance.
- Easily disposed of at its end-of-life.
- Chilled water output around 5 to 7 ℃.
- Readily incorporates other energy source such as solar heated hot water.
Ideal for use with cogeneration systems adsorbtion chillers utilises the readily available heat source and uses minimal electricity. This combination of cooling combined with cogeneration is referred to as trigeneration.
Absorption chillers work in a similar way to adsorption chillers however have a few drawbacks:
- Use water as the refrigerant and lithium bromide which is very corrosive as an absorbent material.
- Ongoing maintenance is required as the lithium bromide (salt) corrodes the chiller components with frequent equipment shut downs needed for maintenance.
- The system produces hydrogen which requires the use of costly palladium cells to remove.
- Continual monitoring of the unit’s operation is required.
- Specialised disposal needed due to hazardous materials used.
- Short useful life - typically last around 7 to 9 years.
If you have more questions or would like to know more about using adsorption chillers as part of a trigeneration system in Australia contact the Inoplex team at 0448 307 282.
Ref: https://www.britannica.com/topic/adsorption-chiller, https://industrytoday.com/adsorption-chillers-vs-absorption-chillers/, http://www.tokyo-boeki-machinery.jp/adsorption_chiller/about.html, http://www.tokyo-boeki-machinery.jp/adsorption_chiller/hikaku.html