Ammonia Is a chemical compound of nitrogen and hydrogen with the formula NH3. It is a colorless gas that is about one half as dense as air at ordinary temperatures and pressures. It has a characteristic pungent, penetrating odor. Ammonia has also been called alkaline air and volatile alkali.
Ammonia in Nature:
Most of the ammonia in the environment comes from the natural breakdown of manure and dead plants and animals. Ammonia can be found in water, soil, and air, and in volcanic gases. Ammonia forms a minute proportion of the atmosphere.
Ammonia as refrigerant:
Ammonia has superior thermodynamic properties, so as a refrigerant it requires less energy to produce a given amount of cooling than other refrigerants.
Refrigeration grade ammonia is 99.98 percent pure and is relatively free of water and other impurities (maximum: 150 ppm water, 3 ppm oil, and 0.2 ml/g non-condensables). It is readily available, inexpensive, operates at pressures comparable with other refrigerants, and is capable of absorbing large amounts of heat when it evaporates.
The Refrigeration Cycle
The refrigerant being used is pure ammonia, which boils at -27 o F.
1.The compressor compresses the ammonia gas. The compressed gas heats up as it is pressurized.
2.The coils on the back of the refrigerator let the hot ammonia gas dissipate its heat. The ammonia gas condenses into ammonia liquid (dark blue) at high pressure.
3.The high-pressure ammonia liquid flows through the expansion valve.
You can think of the expansion valve as a small hole. On one side of the hole is high-pressure ammonia liquid. On the other side of the hole is a low-pressure area (because the compressor is sucking gas out of that side).
4.The liquid ammonia immediately boils and vaporizes (light blue), its temperature dropping to -27 F. This makes the inside of the refrigerator cold.
5.The cold ammonia gas is sucked up by the compressor, and the cycle repeats.
As a refrigerant, ammonia has four major advantages over CFCs and HCFCs:
•An ammonia-based refrigeration systems costs 10-20% less to build than one that uses CFCs because narrower-diameter piping can be used.
•Ammonia is a 3-10% more efficient refrigerant than CFCs, so an ammonia-based system requires less electricity, resulting in lower operating costs.
•Ammonia is safe for the environment, with an Ozone Depletion Potential (ODP) rating of 0 and a Global Warming Potential (GWP) rating of 0.
•Ammonia is substantially less expensive than CFCs or HCFCs
There are two key disadvantages to using ammonia as a refrigerant:
•It is not compatible with copper, so it cannot be used in any system with copper pipes.
•Ammonia is poisonous in high concentrations.
Two factors, however, mitigate this risk:
•Ammonia’s distinctive smell is detectable at concentrations well below those considered to be dangerous.
•Ammonia is lighter than air, so if any does leak, it will rise and dissipate in the atmosphere.
•Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers.
•Ammonia, either directly or indirectly, is also a building block for the synthesis of many pharmaceuticals.
•Ammonia solutions are used to clean, bleach, and deodorize; to etch aluminum; to saponify (hydrolyze) oils and fats; and in chemical manufacture.