ok now some major thinking on you guys now....instead of heat, think cool water, lots of it
a large chilling unit with a 2 inch centrifugal pump driving it, feeding into a three inch header with (now) 14 loops of 5/8 plastic pipe of 600 feet per loop. about 30 psi on the "out" of the pump and only 2 psi on the return at the pump side. the unit is working well and water must be moving quickly, the cooling area of these loops is only 8 feet wide and 2 feet high (like a plastic tepee, in full sun) cooling water is entering at 40 degrees f and returning at no noticeable change, tent is 14 degrees cooler that outside of tent. now the owner is thinking of adding another 28 loops, so I guess mu question would be if there will be enough pressure on the return side as to not cause cavitation at the pump?