How does the melting temperature of ice compare to freezing temperature of hot tap water?
I think the difference between how much warmer a block of needs to get to start melting is small and the amount hot tap water needs to cool before it will freeze is large. These are called phase changes when applied to the different states of solid, liquid, gas and plasma. The energy difference between phase changes is small, but to reverse the “dynamo” a lot of energy is released / removed.
