Ammonia chillers operate by using the principle of refrigeration, where a substance absorbs heat as it changes state from liquid to gas.
At its core, an ammonia chiller works by circulating liquid ammonia through a closed-loop system to absorb heat from a space or process, effectively cooling it down.
The Ammonia Refrigeration Cycle
The process involves several key stages where ammonia (NH₃) acts as the refrigerant, circulating through different components:
1. Evaporation (Cooling)
This is where the primary cooling action happens. Inside the refrigerated space or within a heat exchanger cooling a liquid, extremely cold ammonia (typically a low-pressure liquid) enters the evaporator coil or tubes. The surrounding air or liquid is warmer than the ammonia.
As the warm air or liquid passes over the evaporator, heat transfers into the liquid ammonia. This heat causes the liquid ammonia to boil and turn into a low-pressure vapor. As noted in the reference, "Inside of a refrigerated space, extremely cold ammonia cools the surrounding air. As the ammonia warms, the surrounding air temperature drops. As the ammonia travels through the evaporator, it gradually warms up." This phase change from liquid to gas absorbs a significant amount of heat, thus cooling the surrounding area.
2. Compression (Increasing Pressure and Temperature)
The low-pressure ammonia vapor then travels to the compressor. The compressor is essentially a pump for gas, increasing the pressure of the ammonia vapor significantly. Compressing the gas also increases its temperature. The ammonia is now a high-pressure, high-temperature vapor.
3. Condensation (Releasing Heat)
The high-pressure, high-temperature ammonia vapor then flows into the condenser. Here, the hot ammonia vapor is cooled, usually by outside air or water circulating around the condenser coils. As the ammonia loses heat, it changes back into a high-pressure liquid. The heat removed from the ammonia is expelled into the environment (air or water).
4. Expansion (Reducing Pressure and Temperature)
Finally, the high-pressure liquid ammonia passes through an expansion valve (also called a throttling device or thermal expansion valve). This valve restricts the flow, causing a significant drop in pressure. As the pressure drops, the temperature of the liquid ammonia also drops drastically, becoming the extremely cold ammonia liquid ready to enter the evaporator again to restart the cooling cycle.
Key Components of an Ammonia Chiller System
Understanding the main parts helps clarify the process:
- Evaporator: Absorbs heat from the space/process and evaporates liquid ammonia.
- Compressor: Increases the pressure and temperature of ammonia vapor.
- Condenser: Rejects heat from the ammonia vapor, turning it back into liquid.
- Expansion Valve: Reduces the pressure and temperature of liquid ammonia before it enters the evaporator.
These components work together in a continuous loop to move heat from where it's not wanted (the refrigerated space or process fluid) to where it can be dissipated (the environment).
Why Ammonia?
Ammonia is a popular refrigerant in large industrial and commercial refrigeration systems due to its excellent thermodynamic properties, making it very efficient at transferring heat. While it requires careful handling due to its toxicity and flammability, its efficiency makes it an environmentally preferred choice compared to some synthetic refrigerants.
In summary, ammonia chillers cool by cycling ammonia through evaporation (absorbing heat and cooling the target area, as highlighted in the reference), compression, condensation (releasing heat), and expansion, continuously moving heat out of the system.
