We recommend a flowrate of 2-3 liters per minute per KW of heat to be removed. This is a broad range, but the exact flowrate will depend on your system. We recommend the use of variable speed pumps to adjust the flowrate as needed. Please review our EF Guide to SLIC, which contains a lot of good information on how to size pumps and dry coolers. And write to firstname.lastname@example.org with any questions you have.