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A sort-of follow-up to Why does the International Space Station produce so much methane?

In 2010 Sabatier hardware was integrated into the regenerative environment control. The Sabatier hardware implements the Sabatier process; this retrieves water out of the Carbon Dioxide, Hydrogen present ...

$$\require{mhchem}\ce{CO2 + 4H2 -> CH4 + 2H2O}$$ With a crew of 6, the system is capable of recovering up to 2000 pounds of water annually. I could be wrong, but iirc the reaction liberates some heat-energy in the process.

  • How much heat did the Sabatier hardware add to the annual ISS heat profile?
  • As a corollary, what is the overload capacity built into the thermal management system on the ISS?
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Enthalpy released is about 165 kJ / mol of $\require{mhchem}\ce{CO2}$. 2,000 lb of water is about 50 kmol, requiring 25 kmol of $\ce{CO2}$. Thus long-term average heat output is 165 kJ * 25000 / 1 year = 130 watts, which is trivial compared to the overall ISS heat profile.

The Sabatier equipment probably runs at a peak-to-average power ratio somewhat greater than 1, and there would be some additional heat generated by heating elements, pumps and electronics aside from that liberated by the reaction, but even so the ISS thermal rejection system would have to deal with under a kilowatt from the Sabatier system.

This is pretty small compared to e.g. the overall electrical load of the ISS, which is in the 70 to 100 kW range (and, of course, essentially all that electricity ends up as heat).

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