LOL, I am going out on a limb and say to somehow regulate pressure so that the return from building "B" will be able to overcome building "A"? I could see a lot of issues with that design. I would really have to see the engineers S.O. on that one.
What is the load in the buildings? WSHP's? Was the lower building added to the existing upper building? I am curious to see the complete drawings, if possible. And, like ZeroCool said, the sequence of operation probably explains it. Maybe they are using one tower to maintain two loops at different temps. Driving the tower setpoint to maintain the cooler loop and mixing return water to maintain the other loop slightly warmer?
Yeah , a bit different from your typical condenser water loop . The whole building is now chopped up . It's got the trane self contained units for the floors with free cooling and lil heat pumps on the same loop throughout building . Pumps stay on 24/7 and the tower fan is now on a drive . I think the bottom loop needs both pumps on to overcome the main building loop . How else woould water flow into the tower header when it's piped off it's return . Still don't get it . I know it'll hit me in a sec.