Terms of the Trade: What is Absorption Cooling?

thermal imaging view of absorption refrigerator

Absorption cooling is a method of refrigeration that uses an external heat source such as propane or solar power to provide the energy required to lower temperatures. Absorption refrigeration is a mainly used as an alternative to compressor based refrigeration in applications or areas where electrical service is intermittent or unreliable, too costly, or otherwise unavailable.

Absorption refrigerators use no moving parts and don't have fans or compressors. They use an external heat source for energy and use the heat to cool the interior of the refrigerator. While there are many types of absorption refrigerators, the most common variety use ammonia as a the primary coolant and use ammonia, hydrogen gas and water to power the cooling cycle.

Absorption Cooling Parts

Absorption refrigerators have five primary components.

Generator - Used to generate ammonia gas

Separator - Used to separate the water from ammonia gas produced by the generator

Condenser - Here, the heated ammonia gas is cooled. The condensation that results creates liquid ammonia.

Evaporator - Used to evaporate liquefied ammonia and cool the refrigerator.

Absorber - Used to absorb and filter the ammonia gas from water.

How Absorption Cooling Works

Here is a step by step guide to the process:

Heat from an external source is used to provide energy to the generator.

The generator contains a solution liquid ammonia and water. The heat produced by the generator increases the temperature of the liquid to the boiling point for the ammonia in the solution.

The hot solution of ammonia and water is then passed on to the separator where the water is separated from the ammonia gas.

The ammonia gas then continues its journey and flows upward into the condenser. The condenser is made up of metal coils and fins (usually aluminum) that help to dissipate the heat in the gas. This condenses the ammonia gas back into a liquid.

The liquefied ammonia now enters the evaporator. In the evaporator unit liquid ammonia combines with hydrogen gas and evaporates. This reaction causes a burst of very cold air to be forced into the interior compartment of the refrigerator through vents.

The ammonia and hydrogen gases then flow into the absorber where water that has collected in the separator unit is mixed with the gases.

Introducing water into the ammonia and hydrogen gas mixture causes the hydrogen gas to be released. The hydrogen gas then flows back into the evaporator. The remaining ammonia and water flow again into the generator. Then, the cycle begins again.

Common Applications of Absorption Refrigeration

One of the most popular practical applications of absorption refrigeration is that of refrigerators used in side camper trailers or recreational vehicles. Instead of electric refrigerators, these types of vehicles use refrigerators that are powered with energy created by burning liquefied petroleum gas (LPG). This allows owners of the types of vehicles to avoid using generators or drawing on the power of their vehicle's battery.

Absorption refrigeration is also commonly used to cool machinery or even used to air-condition large buildings using waste heat that is created by gas turbine engines or water heaters. This type of process is efficient and helps to conserve on electricity costs and usage.