FYI I do not have too much experience doing cooling tower designs. I'm looking to replace an existing cooling tower (250 tons) and add a bypass valve for the condensing water.

What should the bypass valve and pipe be sized for? (full flow of the cooling tower, minimum flow of the chiller, or ??)

When going into bypass mode how should the pumping problems be addressed when changes in head occur (open loop to closed loop)? The condensing pumps have VFDs and the new cooling tower will also have a VFD.