What flange said is correct. I guess we need to clarify which system you are talking about because you need two pumps, one for you closed loop chiller-heat exchanger loop and the other to pump your tank through the other side of the heat exchanger, which is an open loop.

A centrif. pump is fine for the closed loop. For the open loop you need to make sure the pump has enough suction head so it doesn't starve. This is just like when you have cooling towers and condenser water pump all on the roof. The pump can really have a tough time if the sump level is not high enough above the pump. You can maybe make a pit for the pump but however you slice it this is something to figure out before you get her all piped out and can't get the open loop side to flow Especially if you go up and over the side of the tank, hmm maybe you could even put the pump into the tank, sump pump like!

Good luck with it