Absorption Chilling

Introduction 

Absorption Chilling is a method, using heat to drive a cooling system, for buildings and industrial processes. This means that Absorption Chilling is the perfect partner for biomass boilers from Wood Energy Ltd as they can be used, not only to provide a building with heat in the winter, but also, cooling in the summer. Given the cost-effectiveness and stability of biomass fuels, very significant reductions in electrical and fossil-fuel consumptions can be made. 

The absorption chiller is a refrigerator that utilises a heat source (biomass boiler) to provide the energy needed to drive the cooling system rather than being dependent on electricity to run a compressor. An absorption chiller is similar to an ordinary compressor refrigerator in that the refrigeration takes place by evaporating a liquid with a very low (sub-zero) boiling point. In both cases, when a liquid evaporates or boils, it takes some heat away with it, and can continue to do so either until the liquid is all boiled, or until everything has become so cold that the sub-zero boiling point has been reached. The difference between the two is how the gas is changed back into a liquid so that it may be used again. An ordinary refrigerator uses a compressor to increase the pressure on the gas, forcing it to become a liquid again. An absorption chiller uses a different method that requires no moving parts and is powered only by heat.

Absorption Chilling and Biomass 

Biomass boilers have a flow temperature of about 90°C which is perfect for the generator, where the refrigerant is separated from the absorbant. Buildings that require winter heat and summer cooling can utilise the cost-effective biomass fuel to provide the heat for the building in the winter and heat for the absorption chiller in the summer. Summer cooling through the use of electrical energy typically represents 10-12% of the total building electrical consumption, whereas the use of biomass reduces this to a typical 1-2% coupled with much cheaper biomass fuel.

The most common uses for absorption chilling are air-conditioning and food refrigeration. The thermodynamic process is not a conventional thermodynamic cooling process based on Charles Law. Instead, it is based on evaporation, carrying heat, in the form of fast-moving (hot) molecules from one material to another material that preferentially absorbs hot molecules. The most familiar example is human sweating. The water from sweat evaporates and is "absorbed" into cool dry air, carrying away heat in fast-moving water molecules. However, absorptive chillers differ in that they regenerate their coolants in a closed cycle, while people drink water recycled outside their bodies. The classic gas absorption chiller cools by evaporating liquid ammonia in a hydrogen environment. The now-gaseous ammonia is then absorbed (dissolved) into water, and then later separated (boiled off from the water) by heat from a biomass boiler. This drives off the dissolved ammonia gas which is then condensed into a liquid. The liquid ammonia then enters the hydrogen-charged evaporator to repeat the cycle. A similar system, common in large commercial plants, uses a solution of lithium bromide salt and water. Water is evaporated under low pressure from the coils that are being chilled. The water is absorbed by a lithium bromide/water solution. The water is driven off the lithium bromide solution using heat. Another variant uses air, water, and a salt solution. Warm air is passed through a sprayed solution of salt water. The spray absorbs humidity from the air which is then passed through an evaporative cooler. Humidity is removed from the cooled air with another spray of salt solution. The salt solution is regenerated by heating it under low pressure, causing water to evaporate. The water evaporated from the salt solution is recondensed, and rerouted back to the evaporative cooler.

Conclusion

Biomass boilers from Wood Energy Ltd are the perfect partner for absorption chilling to provide summer cooling and winter heating. Contact Wood Energy Ltd to discuss your application.