If the gas flow to a duct has stopped and the gas inside stays still, its temperature falls or rises depending on the surroundings as you'd expect.
When the gas starts moving again, its temperature is reset back the temperature it had when it first entered the duct, and any change from its surrounding is discarded. A gas that is flowing is unaffected by its surroundings, or possibly just reset continuously.
There are other ways to trigger this temperature reset as well; just build or remove a piece of duct wherever on the map, and the temperature of all gases in ducts across the map will be reset.
This bug can for example be exploited to lower the temperature in a room enough to freeze carbon dioxide and chlorine, using only a single regulator, a closed loop with hydrogen gas and a little patience.
Fill the loop with hydrogen, let it run through the regulator until it's about -230°C and then stop the regulator, halting the gas. When the temperature in the ducts rises, just build or remove a piece of duct somewhere else, and the gas' temperature will reset and the room will keep getting colder without spending any power at all.
When the room is cold enough, go ahead and pipe in some CO2 or chlorine, and it will liquidize or freeze at the bottom, never bothering you again. Or put a few coal generators in there, they'll stay cool forever and you don't have to worry about any CO2 they produce. With enough patience you could probably liquidize oxygen aswell, if that's your jam.
Steps to Reproduce
- Fill a duct with gas and pipe it through a thermal regulator or two - Make the flow stop, halting the gas - Wait until the temperature has risen a little - Build a piece of duct somewhere, doesn't need to be connected in any way - The gas temperature should now have been reset.
Status: Known Issue
We are aware of this issue and have it logged internally but either we do not have a fix ready yet or we are not planning on addressing the issue in the immediate future.