Absorption chillers and heat pumps- ammonia-water systems. Technology

The properties of the binary ammonia-water mixture NH ₃ -H ₂ O, presented in the article [BE 9 736] , make it possible to design liquid absorption machines, which are described in this article. These absorption machines differ from H ₂ O-LiBr liquid absorption machines on several points (notably the pressure level and the fact that the vapor is a mixture) which have important consequences for the design of the units and the technology used.

For industrial applications where cold is produced at sub-zero temperatures, the single-stage cycle is mainly used, with COP values depending on the temperature of the cold produced, but below 0.5 for sub-zero values. This single-stage cycle is also used for solar-powered chilled water production units for air conditioning. These units have COPs ranging from 0.47 for negative cold to 0.7 for cooling ceilings.

2 or 3-stage cycles are used for lower-temperature industrial refrigeration (down to – 50°C or – 60°C), but require higher hot-source temperatures of up to 175°C.

The GAX cycle (Generator, Absorber, heat eXchanger) is used for liquid coolers for air conditioning and for natural gas heat pumps. A COP of 0.7 is obtained for positive cooling at 7°C, and a COP of _hot of 1.5 is obtained for an air/water heat pump (7/35°C).

As ammonia is a toxic and slightly flammable fluid, units containing more than 2.5 kg of ammonia are subject to rules governing their installation in establishments open to the public. Aerothermal heat pumps with a capacity of less than 70 kW (containing less than 11 kg of ammonia) must be located in the open air, while geothermal heat pumps may be located indoors in an area with authorized access only. Higher-powered industrial refrigeration units must comply with the norme NF EN 378 and therefore be located in premises with authorized access only.

NH ₃ -H ₂ O natural gas (or LPG) heat pump and liquid cooler units are manufactured in medium series for a limited market compared to the H ₂ O-LiBr machine market. Industrial refrigeration units, on the other hand, are...