Absorption systems use fluids and heat sources to create refrigeration or air conditioning without a compressor. Two types are lithium bromide/water and ammonia/water, suitable for different temperature ranges. The process involves five stages and is ideal for off-grid applications.
An absorption system is a means of refrigeration or air conditioning in which cooling is achieved using a combination of fluids or gases and a heat source. Unlike traditional compressor systems, absorption cooling uses a secondary absorbent fluid and the heat from a propane or kerosene flame to create the pressure differential needed to circulate the refrigerant. However, the remainder of the base coolant cooling cycle is shared by both systems. There are two basic types of absorption systems: lithium bromide/water and ammonia/water. The absence of a compressor makes the absorption system suitable for applications where mains power is absent or unreliable.
The main difference between compressor and absorption system is the method used to pressurize and circulate the refrigerant. Absorption coolers do not use a compressor but rather rely on energy from an external heat source to drive the system. This heat source is typically a propane or kerosene flame, although solar heating is becoming increasingly popular as an energy component. Apart from this fundamental drawback, absorption refrigerators and air conditioners use the same basic principle of heat transfer as that of their compressor counterparts.
There are two basic types of absorption systems, each functioning in a similar way but suitable for different temperature ranges. The first is the water/lithium bromide system for applications where temperatures of 32°F (0°C) and higher are required. In these systems, the lithium bromide component is used as the absorbent and water is the cooling agent. The second type of sorption system is the ammonia/water variant used in applications that require temperatures of 32° F and lower. This type of system uses ammonia as a refrigerant and water as an absorbent.
Absorption systems consist of five basic stages: generator, separator, condenser, evaporator, and absorber. The refrigeration process begins in the generator where heat is applied to the refrigerant/absorbent mixture. Here the refrigerant is boiled to form a gas and flows, with the absorbent, to the separator. The two elements are then removed from each other and the refrigerant flows through the condenser. In the condenser, the refrigerant gas escapes by condensation and its heat returns to the liquid state.
The liquid refrigerant then flows into the evaporator located in the room or inside the refrigerator. Here it mixes with a pressurized charge of hydrogen gas which causes the refrigerant to absorb heat from within the space and rapidly evaporate. From the evaporator, the refrigerant and hydrogen gas flow to the absorber where the originally separated absorbent is mixed with them. The absorbent forms a solution and the refrigerant and dispersed hydrogen gas return to the evaporator. It is this phase of the cycle that gives the absorption system its name.
Once this process is complete, the refrigerant/absorbent mixture returns to the generator to resume the cycle. The lack of mains power in absorption coolers makes these systems ideal for motorhomes, recreational vehicles (RVs), boats and caravans. Locations where the electrical grid is unreliable are also good applications for this type of air conditioning and refrigeration. These systems can also make a lot of sense in today’s increasingly conservation-conscious environment.
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