Riding the Pump Curve

Riding the Pump Curve

What is meaning of “secondary pump riding pump curve,” and how do we model it?

“Secondary pump” to me infers a circulating pump on a secondary loop, as opposed to primary equipment or primary loop pumps.

Further recommended reading:

Volume 3: Topics > Central Plant Components > CIRCULATION-LOOP

“Riding the pump curve” infers different things depending on context you haven’t provided yet

  • If flow is supposed to be constant, then “riding the pump curve” simply means the pump’s performance and power input will be read off of the associated pump curves based on the (static) head/flow requirements.  Power input shouldn’t vary much in your simulation while operating (cycling aside), though in the real world you can find issues including blocked strainers, stuck/broken valves, corroding coils/piping, and other system changes over time resulting in long term variances from the designed or as-constructed head pressure.
  • If flow is supposed to be variable, then as flow varies the pump will maintain a single speed (rpm) and draws more/less power as the pressure/head requirement varies further from its design selection point (where the system curve intersects with the pump curve).  There are limits to this degree of variable flow operation with respect to a given pump/impeller intended for single speed operation – some pumps by design can work with a larger range of duty conditions, and other cannot. If flow ranges too far off of the selection you end up with unstable operation and cavitation (vacuum pockets creating boiling fluid – sounds like you’re pumping gravel) – not good for system longevity, and the efficiency of the pump can tank to boot! … This however is why we have and employ options including VSD’s, multi-speed pumps, and staging between multiple pumps.
  • For either case, you can achieve “riding the curve” in eQuest/doe2 by specifying ONE-SPEED-PUMP for the pump’s CAP-CTRL.  Pay mind to the line mentioning that you won’t achieve variable flow operation in the loop if you don’t have one or more 2-way valves specified on the airside tab:

I hope this is helpful!

~Nick

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