Absorption chillers - Water-Lithium bromide systems

The LiBr-water liquid absorption machines discussed in this article are trithermal heat converters [BE 9 734] .

The main application for these machines is the production of chilled water at 7°C from a thermal heat source (hot water, steam, natural gas or fuel oil, etc.), rejecting heat at ambient temperature.

The various cycles used by these machines are presented and analyzed using a spreadsheet to simulate cycle performance as a function of operating conditions.

The technology used and the main features of these units are then discussed.

Manufacturers offer several types of units with different thermodynamic cycles.

Units using a single-effect cycle have a nominal COP (coefficient of performance) of between 0.7 and 0.8 and are supplied with hot water at around 95°C or saturated steam at 100 kPa.

Units using a double-effect cycle have a higher nominal COP of around 1.3, and can be powered either by direct heating with an integrated burner (most often natural gas), or by indirect steam heating (generally at 9 bar/175°C), although many other variants are available (light fuel oil, liquefied gas, gas turbine exhaust gas, etc.). These units consume a small amount of electricity, to drive liquid circulation pumps, whose consumption represents less than 1% of the cooling capacity.

Units using these two types of cycle are mass-produced and account for the vast majority of the global absorption machine market, which is significant with growth of around 4%. In 2018, nearly 13,000 absorption GRLs (liquid chiller units) were sold, worth almost $1,300 million. This absorption LRG market corresponds to 12% of the total LRG market.

This market essentially corresponds to high cooling capacity units (over 200 kW and up to 5 MW). Industrial applications account for 85% of the market, of which double-acting units represent over 80%, with a slightly higher growth rate than single-acting units, while direct-heating units account for almost 50%. The cost per kW of these systems decreases with power.

Alongside these units, triple-effect cycle units with a higher COP of between 1.7 and 1.8, using heat at 200°C, are presented in the article, but for the time being these units have failed to displace the double-effect units.

Finally, heat pumps and thermotransformers, presented in the article, are also offered by several manufacturers, but have not yet met with great success.