We are trying to reduce HVAC cost. One solution is to change Air-cooled VFD to liquid cooled VFD. VFD is 4000hp. Wonder what is the cost difference between Air cooled VFD and water cooled VFD, inclcuding installation? Any idea?
Getting quotes would be the easiest way to find out. I expect it's higher. Generally, you trade cost for installed size and the convenience of being able to dump the VFD heat where you chose (within reason).
Depends a lot on where in the world you are. Getting rid of heat may be very expensive in some areas while the cost is next to nothing in colder areas. Plumbing is not cheap either. And water processing, that some VFDs need means addtional costs. Make sure you get the whole installation cost and the cooling cost before making a cost-based choice.
Preventive maintenance is probably higher for a water cooled unit.