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VFD Pump Control

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Hello, I have a question with regard to a heating hot water loop piped as a primary, secondary heating system.  We currently have a 25hp primary circulator that is controlled by a vfd and dp controller.  The building is a 10 story commercial office building with fin tube perrimeter heating.  The valves are 2 way ddc, tied to a JCI metasys system, controlling to a head pressure setpoint of 20psi.  There is also a 5hp circulator tied into this same loop that feed our 1st floor and lower level areas.  This pump has no control tied to it, running full design rpm.  I am seeing about 10 psi accross the dp controller,  but never see much change in the vfd, no matter what the OAT is.  Valves open or closed, not much of a change.  If another vfd is installed to control the 5hp pump, should we be tracking off the same dp controller, or should another dp controller be added for the lower level and 1st floor loop control?  Any thoughts or suggestions would be greatly appreciated.

Thanks, Brad 
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