Complex sentence: Ice was originally transported from mountains to cities for use as a coolant, and the original definition of a "ton" of cooling capacity (heat flow) was the heat needed to melt one ton of ice every 24 hours.
Split into simpler sentences: Ice was originally transported from mountains to cities for use as a coolant. The original definition of a "ton" of cooling capacity (heat flow) was the heat needed to melt one ton of ice every 24 hours.