It's a closed loop system, as soon as the fluid is pumped out it is immediately replaced. The cycle time I refer to is more of the thermal energy. If you have, say, 1qt of fluid and a pump rated at 1qt/min then we know we have a 1 min cycle time. If the larger lines hold 2qts now we have a 2 min cycle time.
Again, ultimately for heat these are good things, more fluid in the system means more heat capacity.
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