Author Topic: ISS cooling - why ammonia?  (Read 5653 times)

Offline Vultur

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ISS cooling - why ammonia?
« on: 06/28/2016 04:18 am »
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?

Offline Sam Ho

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Re: ISS cooling - why ammonia?
« Reply #1 on: 06/28/2016 05:03 am »
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?

Ammonia has the best thermodynamic efficiency, and is also the lightest commonly used refrigerant. The ISS only uses ammonia in the External Active Thermal Control System. The Internal ATCS uses water. Thus, ammonia hazards are mostly a concern only for EVA, where everyone is already effectively wearing PPE.

Offline Tuts36

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Re: ISS cooling - why ammonia?
« Reply #2 on: 06/28/2016 05:07 am »
My google-fu turned up this article which explains the rationale in some detail.

Offline hop

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Re: ISS cooling - why ammonia?
« Reply #3 on: 06/28/2016 08:29 pm »
The 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.

As ever in the space business, almost every option involves ugly trades.

Offline Vultur

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Re: ISS cooling - why ammonia?
« Reply #4 on: 07/01/2016 05:54 am »
The 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.

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...

Ammonia has the best thermodynamic efficiency, and is also the lightest commonly used refrigerant.

Ah, ok.

Offline Jim

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Re: ISS cooling - why ammonia?
« Reply #5 on: 07/01/2016 11:37 am »

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...


It is not just point of use, but the production, transport and loading activities even before it gets into space that the issue.  More escapes then

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