just a peice of information for you guys, if you have a loop of water, the pump only has to pump uphill the first time to fill the loop, then the will will free flow, think of it as a siphon. so essentially a closed loop has no head pressure cept for the resistance in the line. now the problem is if you get a small air leak your pump will not be able to pump the water high anough and then the still doesnt get enough cooling and therefore it must be supervised very well
In myopnion, the cost of a pump and all the BS that goes along with that is not worth it. The cost of the pump will pay for a lot of cold tap water haha
and it is far less complex, as neat as a closed loop sounds, it is a pain int he but..
I was using a 1000gph pump, and built a cooler out of car heater cores for it and had a furnace fan coolling it haha. It was loud, and annoying and i had to watch it constantly. I hooked up a garden hose fitting, and now all it takes is a trickle of water to cool 6kw, youd be surprised lol. and the other end either goes out to water the grass or wahtever. too easy.
good luck though