Why does the ISS cooling system use ammonia? IIRC it's considered a relatively dangerous refrigerant in Earth industry - is there something specific about the space station that makes it a better choice?
The Internal ATCS uses water. Thus, ammonia hazards are mostly a concern only for EVA, where everyone is already effectively wearing PPE.
Quote from: Sam Ho on 06/28/2016 05:03 amThe Internal ATCS uses water. Thus, ammonia hazards are mostly a concern only for EVA, where everyone is already effectively wearing PPE. However, damage at the interface between the internal / external systems is something they worry about quite a bit (e.g. http://www.spacepolicyonline.com/news/false-alarm-sends-usos-iss-crewmembers-to-russian-segment), as is decontaminating EMUs before returning to the airlock.
Ammonia has the best thermodynamic efficiency, and is also the lightest commonly used refrigerant.
Yeah, that's what made me think of the question. I believe some of the non-toxic/much-less-toxic halogenated options are bad for the ozone layer, but that shouldn't matter on ISS...