Why is ammonia used as a coolant in the ISS truss?
Good question, actually when it comes to fluids as coolant or heat transfer fluids, water and ammonia far and away are superior to any other fluids, and we use both of them on the Station. We use water inside the pressurized modules but it does have some drawbacks and one of them would be that it freezes at 32 degrees Fahrenheit. Where as ammonia doesn’t freeze until we get to minus 108 and we do see those extremes external to the pressurized modules and that is why we use ammonia.
