What primary characteristic makes ammonia unsuitable for large-scale air conditioning?

Ammonia's primary characteristic that makes it unsuitable for large-scale air conditioning is its toxicity. While ammonia can be an efficient refrigerant with excellent thermodynamic properties, it poses significant health risks. Exposure to ammonia can lead to respiratory issues, skin irritation, and other serious health hazards. In an air conditioning application, particularly in large-scale systems where leaks can occur, the risk of harm to both operators and occupants in areas being cooled is a critical concern.

In contrast to this, ammonia’s cost, excessive pressure needs, or flammability, while relevant considerations, do not have the same level of impact on its viability for air conditioning systems. Its toxicity is a major factor that necessitates stringent safety protocols and considerations, ultimately overshadowing its efficiency and other properties when it comes to widespread adoption in large air conditioning systems.